Wonders of the Universe - Brian Cox, Andrew Cohen (2011)
Chapter 2. STARDUST
THE ORIGINS OF BEING
What are we made of? This is an old question, maybe one of the oldest, and one that thinkers and scientists have been working hard to answer since ancient times. This work continues today, and it may be that by the time you read this book the story of the search for the building blocks of the Universe will have another chapter. Such is the power, excitement and rate of progress of modern science. This chapter is the story of how those building blocks were created in the very early Universe, fused into more complex structures over billions of years in the furnaces of space, and delicately assembled by the forces of nature into planets, mountains, rivers and human beings.
The Large Hadron Collider (LHC) is the highest energy particle accelerator at CERN (the European particle physics laboratory near Geneva, Switzerland). In this huge machine, 27km (17 miles) in circumference, proton beams are accelerated so that they collide head-on. The resultant particles can be detected and recorded so that scientists can then try to understand how they fit together.
DAVID PARKER / SCIENCE PHOTO LIBRARY
The ancient Greeks thought deeply about the question of what we are made of, although they lacked the scientific methodology and technology to arrive at a definitive answer. This led to many competing hypotheses, including some that got close to our modern view: we are all made out of smaller pieces. That there are the smallest building blocks of matter (indivisible basic units that can be fitted together to build the world) was termed the ‘atomic hypothesis’, a theory usually credited to two thinkers – Leucippus and Democritus – in around 400 BC. They held that the world was created from an infinite number of different types of indivisible and indestructible atoms. Each had a different shape, allowing them to fit together neatly to build large objects. So, iron was made of one type of atom, water of another, human flesh of another, and so on. They thought atoms possessed the properties of their real-world substances – water atoms were slippery, while metal ones were shaped so that they locked together to produce very hard substances. We now know that this is not only wrong, but a gross overcomplication. While their hypothesis correctly stated that the world is made from smaller pieces, you don’t need an infinite number of atom types to build the complexity around us. A human is made of the same stuff as a rock; a fish of the same stuff as the Earth; the sky of the same stuff as the oceans. Enumerating the basic building blocks and understanding how they fit together is the province of the science of particle physics, and this quest continues at the Large Hadron Collider at CERN, in Geneva.
By early 2011, we had discovered that the Universe is composed of twelve basic building blocks, only three of which are required to build everything on our planet, including our bodies. These three components, known as the up and down quarks and the electron, can be assembled into the more familiar protons and neutrons – two up quarks and a down quark make a proton, and two down quarks and an up make up a neutron. In turn, the protons, neutrons and electrons make up the chemical elements – ninety-four of which are known to occur naturally – including the basic chemical elements hydrogen, carbon, oxygen, iron, gold and silver
THE CYCLE OF LIFE
Fifteen miles northeast of the Nepalese capital city of Kathmandu, three small streams come together to mark the beginning of one of the holiest rivers in the world. At its source the Bagmati is a fast-running mountain stream, but by the time it winds through the Kathmandu valley and enters the great city of the Himalayas it has become a wide and majestic river.
In the eastern part of the city, where the river’s mythical power is at its greatest, stands the fifth-century Pashupatinath Temple, one of the most sacred sites in the Hindu world. Pilgrims come from all over India and Nepal to worship there and pay their respects to the god Shiva.
I have always found the Hindu faith fascinating; it is rich and complex, a disorientating mix of mythology and philosophy, a continual and jagged juxtaposition of temples, holy sites, rituals and everyday life that produces a joyful assault on the senses. Pashupatinath is no exception. It is at once vibrant and ethereal, a place where the colours and noise of India meet the gentle philosophy of Tibet and the hybrid dissolves into the crystal-clear, high Himalayan air in the smoke of a thousand burning bodies on the funeral pyres lit at this holy place. The scent of burning flesh mixes with incense and tinkling bells, and the sound of chanting Monkey Gods continually interrupts the calls of market traders.
A central tenet of Hindu philosophy is the concept of the Trimurti – the triad of the three fundamental aspects of the Supreme Being, represented as the great gods Brahma, Vishnu and Shiva. Lord Brahma is the creator of the Universe, Lord Vishnu the preserver, and Lord Shiva the destroyer. Shiva represents darkness, as an angry god who will eventually bring an end to Earth, yet in Hinduism this destruction is seen as an essential part of the cycle of life, because in order for new things to be created, the old order must first be destroyed. Shiva is therefore also a regenerative or reproductive power, part of the endless cycle of death and rebirth that is central to the Hindu belief system. This is why the Pashupatinath Temple and the river it stands beside are revered as places to die.
The Bagmati River is lined with funeral pyres burning the bodies of the deceased.
For Hindus, the passing of a loved one is a stage in the endless cycle of death and rebirth that is central to their beliefs. Cremations are a familiar sight along the holy Bagmati River; the body is dipped in the river three times before cremation, and at the end of the ceremony the chief mourner must bathe in the river’s water, often accompanied by the other attendant mourners.
Hindus believe that the purpose of a soul’s time on Earth is to work through a cycle of rebirth and reincarnation until it becomes perfect. Only then can it be reunited with the Universal Soul and be freed from its material existence. The Bhagavad Gita says: ‘Just as a man discards worn-out clothes and puts on new clothes, the soul discards worn-out bodies and wears new ones’. By having your body cremated on the riverbank beside Shiva’s Pashupatinath Temple, it is believed that your soul will be released from the worn-out body as quickly and easily as possible.
According to the Nepalese Hindu tradition, the dead body must be dipped three times into the Bagmati River before cremation. The chief mourner, usually the first son of the deceased, lights the funeral pyre and must bathe in the waters of the holy river immediately after the cremation. Many of the relatives who join the funeral procession also bathe in the river or sprinkle the holy water on their bodies. This makes the river bank a strange and crowded place. To my British eyes it is somewhat shocking, because death is rarely, if ever, paraded like this; but here in Kathmandu it is not seen to be insensitive to wander between the pyres as the relatives and friends go through their rituals.
In Hindu tradition the human body consists of five elements: air, water, fire, earth and ether. Remarkably, according to modern science, this is overcomplicated, but their belief about what happens to these elements after death parallels our modern understanding of how the world works.
Underlying the cremation ceremony is the conviction that the elements of the body vacated by the soul are returned to Earth to be re-used and recycled. Death is therefore not an end for the immortal soul or the mortal flesh, it is simply the conclusion of one stage of existence and the beginning of another; part of a natural cycle of death and rebirth. As far as the atoms and molecules in our bodies are concerned, modern science is in complete agreement with that idea. When I die my constituents aren’t going to be magically destroyed; they will be returned to Earth and, given enough time, they will become part of some other structure.
Of course, Hinduism isn’t alone in having rich and lyrical stories about the origin and evolution of Man and the Universe. Virtually every society and every religion around the world has at its heart a creation story that explains where we come from, how we came to be here, and what will happen to us when we die. This suggests that curiosity about our origins is an innate, perhaps even a defining part, of the human condition.
Underlying the cremation ceremony is the conviction that the elements of the body vacated by the soul are returned to Earth to be re-used and recycled… As far as the atoms and molecules in our bodies are concerned, modern science is in complete agreement with that idea.
In common with the great systems of thought throughout history, modern science has its own creation story to tell – one based on physics and cosmology. It can tell us what we’re made of and where we came from – in fact, it can tell us what everything in the world is made of and where it came from. It also answers that most basic of human needs: to feel part of something much bigger, because to tell this story you have to understand the history of the Universe. It also teaches us that the path to enlightenment is not in understanding our own lives and deaths, but in understanding the lives and deaths of the stars
The Dunhuang star chart dates back to AD 700 and is the oldest existing star chart. It was named after the place where it was found along the Silk Road trade route in northern China (in the twentieth century) and is now owned by the British Library. It depicts the stars in the sky according to the Chinese constellation tradition.
MAPPING THE NIGHT SKY
The moment you leave a city and experience a truly dark night sky, it becomes obvious why our ancestors spent a great deal of time looking up at the stars. They are a bewildering array; a patterned silver canopy self-evidently not devoid of meaning or purpose. For thousands of years ancient astronomers endeavoured to capture and catalogue every light; to observe, log and name as many of these distant suns (for we now know their true nature) as they could. The oldest-known record of a star chart may be over thirty thousand years old. A carved ivory mammoth’s tusk, discovered in Germany in the late 1970s, appears to be imprinted with a pattern that resembles the constellation of stars we now call Orion. In France, cave paintings have been discovered which reveal that humans were mapping the night skies tens of thousands of years before the great civilisations of antiquity began to slowly explore the Universe in more detail.
This celestial map shows a more detailed, highly illustrated view of the constellations according to Dutch cartographer Frederik de Wit in the seventeenth century.
For thousands of years ancient astronomers endeavoured to capture and catalogue every light; to observe, log and name as many of these distant suns (for we now know their true nature) as they could.
The Egyptians were one of the first ancient cultures to not only map the night sky but to name some of the stars they observed. They called the North Star the ‘star that cannot perish’, and they also recorded the names of constellations. The Sumerians and Babylonians went a step further by writing down these early names and patterns and creating astronomical catalogues that listed and grouped stars in ever-increasing complexity. Greek, Chinese and Islamic astronomers all continued to build ever more complex systems of classification, with many stars today still being referred to by their original Arabic names.
To the ancients, the stellar backdrop had a deceptive permanence that no doubt motivated them to record and mythologise the patterns they saw. But in AD 185, for the first time in recorded history, a particular type of fleeting addition to the lights in the night sky was observed and documented. Understanding the nature of this rare and spectacular phenomenon eventually led us beyond merely naming the stars and enabled us to tell the story of their births and deaths.
In AD 185, Chinese astronomers witnessed a brightness in the sky comparable to that of Mars, and this remained for eight months. This phenomena was the first recorded occurrence of a supernova explosion, but it was not until late 2006 that the remains of this cosmic event were identified. This picture, taken by the Chandra X-ray Observatory, shows an object now known as RCW 86. The image shows low-, medium-and high-energy X-rays in red, green and blue respectively. It was the study of the distribution of X-rays with energy, combined with measuring the remnant’s size, that enabled scientists to conclude that RCW 86 was created by the explosion of a massive star around 8,000 light years away.
In late 2006, the remains of the cosmic event of AD 185 that illuminated the skies and minds of Chinese astronomers almost two thousand years ago was identified. The picture above, taken by the Chandra X-ray Observatory, is that of the object known as RCW 86. This object is thought to be the still-glowing remains of one of the most powerful events in our universe – a supernova explosion.
Supernovae are the final act in the lives of massive stars, colossal explosions in which a single star can shine as brightly as a billion suns. If RCW 86 is the remains of the AD 185 supernova, then the ‘guest star’ described by the Chinese astronomers that glowed brightly in the skies for eight months before fading from view was around 8,000 light years away – a quite colossal distance for something to shine so brightly in our skies. The ancient astronomers didn’t know it at the time, of course, but they had documented the first clear evidence that the stars must all eventually die
Above our heads a story of life and death is being told in spectacular fashion. This tale begins in the vast stellar nurseries where new stars burst into life. These fertile areas of star formation are known as nebulae and are among the most beautiful structures in the skies. One of these, the Orion Nebula (pictured far right), is perhaps the most studied astronomical object. It is usually credited as being discovered by Nicolas-Claude Fabri de Peiresc in 1610, but there is evidence from folk tales that the Mayans knew of the faint smudge beneath the stars of Orion’s belt. It can be seen with the naked eye in a very dark clear sky, and it is this complex, ever-changing formation that has taught us most about how stars are born.
The Omega Nebula (the Horseshoe, or Swan, Nebula) is a vast interstellar cloud that is over fifteen light years across and illuminated by hundreds of bright young stars. These stars, depending on their masses, will burn for hundreds of millions or billions of years, sending a constant stream of light across the Universe until their voracious hunger depletes the hydrogen in their cores and forces them to expand and transform into giants.
As they near the end of their lives, the most massive stars are transformed into colossal giants – such as the red Mira, whose radius is 400 times that of our sun and only just clinging onto life. When the end finally comes for stars like these, the ensuing supernova explosion will leave only a faint trace of the star. For the largest stars, the supernova will leave a black hole behind – an object so dense that even light cannot escape its clutches. Slightly smaller stars will end their post-supernova days as neutron stars, which we detect by the lighthouse beam of radiowaves they emit as they spin every few seconds or less.
Stars much smaller than Mira won’t go out with a bang. Such relatively cool stars are called red dwarfs and are the most common type of star in our galaxy. Perhaps the most famous of these we have studied is Gliese 581. Just over twenty light years away from Earth, this star has been the subject of intense observation in recent years due to the discovery of at least six exoplanets orbiting around it. Most excitingly, planet Gliese 581 g is thought to orbit within the habitable zone of the star and so is considered a prime location for the search for extraterrestrial life
These fascinating ultraviolet images, taken by NASA’s Galaxy Evolution Explorer, show a star named Mira speeding across the sky and leaving behind it an enormous trail of debris. This material is in fact ‘seeds’ which will be recycled to create new stars, planets and possibly even life, as it travels through our galaxy.
Known as the Horseshoe, or Swan, Nebula, this molecular cloud is also often called the Omega Nebula, due to its similarity in shape to the Greek letter Omega. Ultraviolet light from a cluster of massive young stars buried within the nebula make the surrounding gas glow. This image was taken by the European Southern Observatory’s 3.6-metre (11.8-foot) telescope in La Silla, Chile.
Perhaps the most studied astronomical object, the Orion Nebula is also one of the most beautiful structures in the sky. On over 100 orbits of Earth between October 2004 and April 2005, NASA’s Hubble Space Telecope captured this nebula in one of the most detailed astronomical images ever produced. On a clear, dark night sky this impressive formation – which includes more than 3,000 stars of varying sizes – can be seen with the naked eye. This complex, constantly evolving formation has provided scientists with crucial insight into how stars are formed.
The Venus transits of our sun are a rare occurrence, they only happen twice in eight years and won’t be repeated for another 100 years. The last transit happened in 2004, with another due in 2012. We will have to wait until 2116 for the next one.
This is a composite image of Venus transiting the Sun on 8 June 2004. Venus can be seen from Earth as a small black disc moving across the face of the Sun.
ECKHARD SLAWIK / SCIENCE PHOTO LIBRARY
HOW TO FIND EXOPLANETS
One of the most exciting areas of current astronomical research is the hunt for planets around other stars – known simply as exoplanets – which are potential homes for extraterrestrial life. Until recently such a search would have been impossible, as planets are too faint to see over interstellar distances, however, thanks to new modern instrumentation, we are now able to detect the telltale signals of exoplanets using two main techniques: the radial velocity method and the transit method. With these techniques, individual planets and even planetary systems have been discovered around hundreds of stars. Masses of these extrasolar planets range from a few times that of Earth, to the size of 25 Jupiters. Whether a planet could support life depends on its distance from the parent star. Around each star is a ‘habitable zone’, in which temperatures are suitable for water to exist as a liquid. The size of this zone depends on the energy output of the star; the faintest ones have the closest, narrowest zones. The red dwarf Gliese 581 is believed to have at least one planet within its habitable zone.
Nathalie Lees © HarperCollins
As we observe all the cosmic structures around us in spectacular detail, each tells us something different about the life cycle of the stars. However, something much deeper can be learnt from understanding the existence of stars: they are the ultimate origin of all but the simplest of Leucippus’ and Democritus’ long-sought-after atoms, and as such are the building blocks of ourselves. To comprehend how the stars could play such a vital role in our existence, we must momentarily step back from the skies and come firmly back down to Earth.
The largest mountain range in the world, the Himalayas is also the youngest. This panorama, taken from the top of Kala Pattar in the Sagarmatha National Park, Nepal, shows only a fraction of its scale. Understanding the creation of these impressive mountains helps us to answer many questions about the structure of all living elements in the Universe.
THE ORIGINS OF LIFE
The first step in understanding how the lives of stars are precursors to our own lives is to discover exactly what we are made of. There is possibly no more beautiful, and perhaps no more instructive, place on Earth to begin this journey than in the shadow of the world’s tallest mountain range. With over 100 peaks exceeding 7,200 metres (23,620 feet), the Himalayan range is truly a land of giants; nine of the ten highest mountains on Earth are part of the Himalayas. The greater Himalaya is home to forty-five of the world’s top fifty highest peaks. Spectacularly beautiful, it is the sheer scale of these mountains that hides a fascinating and instructive first step on the road to understanding the building blocks of the Universe. Despite their majesty, just a few tens of millions of years ago these mountains were something very different.
As well as being the largest mountain range on the planet, the Himalayas is also one of the youngest. Just seventy million years ago (a very short time in geological terms) the Himalayas didn’t exist. The relentless movement of Earth’s tectonic plates shaped these mountains in a geological heartbeat. As the Indo-Australian plate collided with the Eurasian plate at the rate of about 15 centimetres (6 inches) a year, the ocean floor in between began to crumple and rise up to form the mountain range. This means that much of the rock out of which these towering peaks are made was formed at the bottom of an ocean, only to be lifted up thousands of metres into the air over a few short millions of years.
The evidence for this extraordinary journey is not difficult to find. If you look closely at any piece of Himalayan limestone you will see it has a chalky, granular structure. What you are looking at are the petrified remains of sea creatures – the bodies and shells of coral and polyps that died millions of years ago in a long-lost ocean. Given a relatively short timescale and a bit of pressure, these biological remains are quickly converted into solid rock. Limestone can also be formed by the direct precipitation of calcium carbonate from water, although the biological sedimentary form is more abundant. We know that the Himalayan limestone is predominantly biological because we have found fossils at the top of Mount Everest! There is perhaps no better example of the endless recycling of Earth’s resources that has been going on since its formation almost five billion years ago.
We humans are also very much part of that system. As unsettling as it may sound, every atom in your body was once part of something else. It may have made up an ancient tree or a dinosaur, and you’ll be pleased to know it was certainly part of a rock. The reason this can happen – that the rocks of Earth can become living things and that living things will eventually die and become rocks again – is simple: everything in the Universe is composed of the same basic ingredients
When you are presented with the sheer magnitude of the Himalayas and the towering peak of Mount Everest, it is hard to believe that these huge mountains started off life at the bottom of an ocean.
Natural recycling at its most impressive. The Himalayan limestone has been proved to be predominantly biological, due to the quantity of fossils of sea shells and creatures that have been found at the summit of Mount Everest.
DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Periodictable.com © 2010 Theodore Gray
THE PERIODIC TABLE
For many people the Periodic Table will provide a strong echo of the school science laboratory. At its simplest, this chart is a list of the chemical elements, fundamental units of matter, which were considered to be the smallest building blocks of the world. However, this table is much more than just a list. Although elemental theories of matter were first postulated in Greece, it wasn’t until 6 March 1869 that the Russian chemist Dmitri Mendeleev finally tamed the ever-expanding list of the basic constituents of matter. Mendeleev’s genius was to arrange the list of the sixty-six then-known elements into a table according to their chemical properties. In the process, the table not only provided a neat way of grouping the elements according to their properties, but also predicted the existence of eight elements yet to be discovered. Over the next thirty years, all eight were discovered, including gallium and germanium, and were found to have the exact properties predicted by Mendeleev’s table. The number of elements continued to grow, and by 1955 the one-hundred-and-first element was discovered (named Mendelevium as a tribute to the father of the Periodic Table) by a group of scientists at the University of California, Berkeley. To date, 118 elements have been categorised, the latest of which, ununseptium, was successfully synthesized and detected by a Russian– US team in April 2010.
Starting with hydrogen and ending with plutonium, the first ninety-four elements of the Table have been found occurring naturally on Earth. These elements are nature’s building blocks; the remaining twenty-four elements, can only be created artificially and live for very short periods of time. Using these ninety-four elements you can explain all of biology and chemistry without knowing about the underlying structure of protons and neutrons, electrons and quarks. This is because you need very high energies and temperatures to break apart the elements – a condition that only exists naturally deep inside the stars.
The first step of our journey to explain where we come from is to understand the origin of these ninety-four elements. But first we must discover how we know that everything we see in the sky is made of the same stuff as us on the ground
THE UNIVERSAL CHEMISTRY SET
Surprising as it sounds, we know what every star, planet and moon in the observable Universe is made of, despite the fact that there is only one other place in the Universe that humans have actually visited in person.
On 21 July 1969, Neil Armstrong and Buzz Aldrin became the first humans to set foot on another world. They spent 2 hours, 36 minutes and 40 seconds walking on the surface of the Moon, but it wasn’t until the last half hour that they carried out one of their most important scientific tasks. Using basic geological tools, Buzz Aldrin drove two core tubes into the lunar surface to collect the most famous rock samples taken in history. By the time they’d finished hammering and scooping up samples they had collected 22 kilogrammes (47 pounds) of lunar treasure. After using a pulley system to lift their scientifically priceless cargo on board, they closed the hatch and went to bed. As the two astronauts slept alongside the precious lunar rocks, the United States could justifiably claim to have won the greatest and arguably most glorious political victory in human history. For one rare moment, a political victory was also a triumph for all mankind.
However, it is not widely known that as the Apollo 11 lunar module rested on the Moon, a Soviet spacecraft was also in lunar orbit. The unmanned Luna 15 was the Soviets’ third attempt to land on the Moon and collect lunar rock samples. Launched three days before Apollo 11, Luna 15 was a last-ditch attempt to win the scientific race to return rock samples from another world. Unfortunately, although Luna 15 successfully began its descent to the Moon’s surface, it crashed into it shortly afterwards. Only Apollo 11 returned with moon rocks, which continue to be analysed to this day in the high-security labs of the lunar sample building in Houston, Texas.
Despite forty years of study, one thing has been clear pretty much from the start: these priceless examples of alien geology are remarkably similar to rocks found on Earth. In the main, they are composed of the common rock-forming elements oxygen, silicon, magnesium, iron, calcium and aluminium, but there is absolutely nothing on the Moon’s surface that couldn’t be found here on Earth.
Since Apollo 11’s success, we have landed on Mars and Venus, parachuted into Jupiter’s atmosphere, touched down on Saturn’s moon Titan, and visited asteroids Eros and Itokawa and the comet Tempel 1. Each time the story is the same; the Solar System is made of the same stuff as we are. To date, eight landings on our nearest neighbour, Mars, have allowed us to explore the planet’s geology in intimate detail. We now know Mars is rich in iron, which has oxidised to form its familiar rusty red colour, and that Martian soil is slightly alkaline and contains elements such as magnesium, sodium, potassium and also chloride. We also know that Venus’ thick atmosphere is full of sulphur, and the planet Mercury is a large metal ball of iron with a thin crust comprised mostly of silicon. Even at the very edge of the Solar System, billions of miles away from Earth, we have discovered that Neptune is rich in organic molecules such as methane, a substance we find in abundance on our planet. Again and again we find there is much to discover in our solar system, but there are never new elements to unearth. From a scientific perspective this is unsurprising, because long ago Mendeleev’s table revealed there isn’t any room for other light elements in nature – we have discovered the full set. It would take a change in the laws of physics to discover something on the surface of another world that doesn’t fit into Mendeleev’s scheme, but from the explorer’s perspective, seeing is believing!
On 21 July 1969, Neil Armstrong and Buzz Aldrin became the first humans to set foot on the Moon. This successful landing also opened up infinite possibilities for scientists to understand the formation of the lunar landscape. This photo shows Aldrin collecting some of the lunar rock samples that they took back to Earth for analysis.
The Apollo 11 lunar mission was launched from the Kennedy Space Center, Florida, on 16 July 1969 and safely returned to Earth on 24 July 1969, complete with its priceless cargo of samples from the Moon’s surface. The first container was transferred to Ellington Air Force Base and was taken directly to the Lunar Receiving Laboratory at the Manned Spacecraft Center (MSC) in Houston, Texas.
Once safely returned to Earth, the treasures from the Moon, including rock samples, were painstakingly analysed at a high-security laboratory, and are still being used for analysis today.
Again and again we find there is much to discover in our solar system, but there are never new elements to unearth.
This false-colour photograph of Neptune was taken by Voyager 2. This image has enabled scientists to discover that the planet is rich in organic molecules such as methane.
So what about the rest of the Universe? How universal are these elements across the far reaches of the cosmos? Could it be that there are places in the distant Universe where the laws of physics are different? This is a legitimate question – we shouldn’t simply assume that everything at the edge of the visible Universe, billions of light years away, operates exactly as it does here, no matter how persuasive the arguments from theoretical physics. Experiment and observation are the ultimate reality check. It may seem impossible to presume that we could ever answer this question directly and discover what the stars are made of, because they are so far away (they may indeed remain untouchable forever), but in fact we knew what the stars were made of long before we got our hands on that first piece of lunar rock
WHAT ARE STARS MADE OF?
Over a simple campfire I recreated the experiments of Gustav Kirchhoff and Robert Bunsen that made such a major impact in the development of quantum theory. Just as they discovered 150 years ago, when I threw the copper into the fire it burned with a spectacular blue flame.
The Sun, the burning star at the heart of our solar system, is 150 million kilometres (93 million miles) away from Earth. Beyond that, the nearest known star, the red dwarf Proxima Centauri, requires a journey of over four light years or forty thousand billion kilometres (twenty-five thousand billion miles). We have learnt a lot about Proxima Centauri since it was discovered by Robert Innes at the Cape Observatory, in South Africa, in 1915. It is thought that Proxima Centauri is part of a triple star system with its neighbouring binary star system, Alpha Centauri A and B, and although it cannot be seen with the naked eye, we have been able to measure its mass and diameter and chart its brightness across the last 100 years. Despite the fact that our only contact with these neighbouring stars, and with any star other than our Sun, is the light that has crossed the Universe to reach us, we have been able to go much further than simply cataloguing their vital statistics. We can measure the precise constituents of any and every visible star in the sky, because encoded in the light that rains down on Earth is the key to understanding what they are made of. It is all made possible by a particularly beautiful property of the elements.
The tale of how we learnt to read the history of the stars in their light began with the work of Isaac Newton in 1670. In his ‘Theory of Colour’, Newton demonstrated that light is made up of a spectrum of colours, and that with nothing more complicated than a glass prism you can split the white light of the Sun into its colourful components. Almost 150 years later, the German scientist Joseph von Fraunhofer made a startling discovery about the solar spectrum whilst calibrating some of his state-of-the-art telescopic lenses and prisms. Lying within the solar spectrum, Fraunhofer documented the existence of 574 dark lines; there were literally hundreds of gaps – missing colours in the Sun’s light. Unaware of the significance of this discovery at the time, Fraunhofer carefully mapped their positions in great detail. He went on to discover black lines in the light from the Moon and planets, and from other stars. These are now known as Fraunhofer lines.
Further work by two more of the great German scientists of the nineteenth century, Gustav Kirchhoff and Robert Bunsen (perhaps best known to schoolchildren everywhere as the inventor of the Bunsen burner), finally gave meaning to these lines. They surmised correctly that these black spectral lines were the fingerprints of the chemical elements in the atmosphere of the Sun itself. Across 150 million kilometres (93 million miles) of space, the light of our star had carried the signature of its constituents to us.
Kirchhoff and Bunsen’s discovery was purely empirical – they had observed that when gases are heated on Earth they do not simply glow like a piece of hot metal, they give off light of very specific colours – and interestingly those colours depend only on the chemical composition of the gas and not on the temperature. In particular, each chemical element gives off its own unique set of colours. The element strontium, for example, burns with a beautiful red colour, sodium with a deep yellow, and copper is a haunting emerald green.
The two German scientists also noticed that the missing black lines in the solar spectrum corresponded exactly to the glowing colours of the elements. There are, for example, two black lines in the yellow part of the Sun’s light that correspond exactly to the two distinct yellow emission lines of hot sodium vapour. You will be familiar with this mixture of two very slightly different yellows – it is the colour of sodium streetlights.
Interestingly, Kirchhoff and Bunsen had no idea why the elements behaved in this way, but this didn’t matter if all you wanted to do was to match the signatures of elements observed on Earth with the signatures in the light from the Sun and stars. It wasn’t until the turn of the twentieth century that an explanation for this strange behaviour of the elements was discovered. The answer lies in quantum mechanics, and the spectrographic work of physicists and chemists such as Kirchhoff and Bunsen was a major motivating factor in the development of the quantum theory. Elements emit and absorb light when the electrons surrounding their atomic nuclei jump around. The key insight that led to quantum theory was that electrons can’t exist anywhere around a nucleus like planets around a star, but they are instead placed in specific, very restrictive ‘orbits’. The deep reason for this is that electrons do not always behave as point-like particles of matter. They also exhibit wave-like properties, and this severely restricts the ways in which they can be confined around the atomic nucleus. What happens at a microscopic level when an atom absorbs some light is that an electron jumps to a different, more energetic, orbit and it emits light when the electron falls back from a higher to a lower energy orbit. The difference in energy between the lower orbit and the higher orbit must correspond exactly to the energy of the light absorbed or emitted.
In the early nineteenth century, German scientist Joseph von Fraunhofer documented the existence of 574 dark lines within the solar spectrum. This diagram is a visual representation of these Fraunhofer lines.
Spectographic investigations have revealed that Sirius, the dog star, is metal-heavy, with an iron content three times that of the Sun.
Isn’t it simply wonderful that just by looking at the light from those twinkling stars we can tell what those fiery worlds, so far away, are made of?
Although Polaris, the pole star (top and middle), is 430 light years away, we know by looking that is has about the same heavy element abundance as our sun, but markedly less carbon and a lot more nitrogen. Vega (bottom), meanwhile, as the second-brightest star in the northern sky, consists of only about a third of the amount of metals as our sun.
However, quantum theory also stipulates that light should not always be thought of as a wave. Just like electrons, light can behave as both a wave and a stream of particles. These particles are called photons. Now, here is the key point: photons of a particular energy correspond to a particular colour of light, so red photons have a lower energy than yellow photons, which have a lower energy than blue photons. Since each element has electrons in unique orbits around the nucleus, this means that each element will only be able to absorb particular photons in order to move its electrons around into higher energy orbits. Conversely, when the electrons drop from higher to lower energy orbits, they will only emit photons of a particular energy and therefore a very particular colour. This is what we see when we observe the elements emitting or absorbing particular colours of light. We are in a very real sense seeing the structure of the atoms themselves.
When looking at a spectrum of light from our sun you can see hundreds of Fraunhofer lines, and each and every one of those corresponds to a different element in the solar atmosphere which absorbs light as it passes through. From sodium in the yellow, through iron, magnesium, and all the way across to the so-called hydrogen alpha line in the red, the signatures of each of the elements are encrypted in the solar code.
So by looking at these lines in precise detail you can work out exactly which elements are present in the Sun. This turns out to be roughly 70 per cent hydrogen, 28 per cent helium, and the remaining 2 per cent is made up of the other elements.
It is worth repeating here that you can apply this theory not only to the Sun, but for any of the stars you can see in the sky – which allows us to measure the constituents of their atmospheres with extraordinary accuracy. Isn’t it simply wonderful that just by looking at the light from those twinkling stars we can tell what those fiery worlds, so far away, are made of?
These spectrographic investigations of the light from the cosmos have confirmed what our scientific intuition suggested to us: wherever we look, we only ever see the signatures of the set of ninety-four naturally occurring elements that we have collected and identified here on Earth.
So it is clear that we are connected in a very real sense to the whole of the Universe – with its hundreds of billions of stars across billions of galaxies – because we are all intrinsically made of the same stuff. And, as we will explain, there is one very simple reason for that: everything in the Universe shares the same origin
THE EARLY UNIVERSE
In order to understand where we come from we have to understand events that happened in the first few seconds of the life of the Universe. When the Universe began it was unimaginably hot and dense – we literally don’t have the scientific language to describe it. It was beautiful in a very real sense. There was no structure, there was certainly no matter, and it was exactly the same whichever way you looked at it. It’s a difficult concept to grasp, but we can get some idea of what happened to the early Universe by looking at the behaviour of one of the most common substances on Earth: water.
Water is one of the most common substances on Earth, but it can produce some of the most spectacular geological wonders on our planet. The El Tatio Geysers in Chile are just one example of water’s awesome activity.
© Charles O’Rear/CORBIS
One of Earth’s most incredible natural wonders, the El Tatio Geysers make up the largest geyser field in the world. As they are located at a height of 4,200 metres (13,800 feet) in the Chilean Andes, they are also the highest.
EL TATIO GEYSERS, CHILE
High in the Andes Mountains, in the far north of Chile, you will find the spectacular El Tatio Geysers. Erupting at 4,200 metres (13,800 feet) above sea level, this is one of the geological wonders of Earth’s Southern Hemisphere. Not only is it one of the largest geyser fields in the world, it is also one of the highest. For those who journey here to witness the eruption of the jets of water skywards there is only one time to visit – sunrise.
In the early morning, as the Sun begins to peer over the horizon, the combination of super-heated water and freezing cold air produces a rare phenomenon. Like all geysers, the boiling water delivered to the surface by the geological plumbing bursts out and flashes into steam, forming the majestic columns. But here, because of the high altitude and bitter temperatures, the steam rapidly condenses and returns to its frozen state, covering the ground with sheets of ice. It is surely one of the most spectacular naturally occurring locations on the planet in which you can see water in all three of its phases: liquid, vapour and solid ice. It is this rapid transformation of water through its three familiar phases that provides us with a nice analogy to discuss events that happened in the very early life of the Universe.
A water molecule is made up of two chemical elements: oxygen and hydrogen. Oxygen and hydrogen atoms are symmetric when they are alone and uncombined. This particular use of the word symmetric is perhaps unfamiliar; what is meant in this context is that the atoms themselves would look the same no matter what angle you viewed them from. In the language of physics, this is called rotational symmetry. A perfect sphere has perfect rotational symmetry, because whichever way you look at it or spin it around it looks exactly the same. When an oxygen atom combines with two hydrogen atoms to form a water molecule – H2O – this rotational symmetry disappears because the water molecules have a particular shape – there is an angle of 105 degrees between the hydrogen and oxygen atoms. A physicist would say that the symmetry is now broken, because the water molecule has a distinct orientation. We can break the symmetry of water still further by cooling down all the molecules until they stick together and solidify into ice. Now the crystals of ice are beautiful and almost impossibly intricate; full of structure and a complexity that completely hides the perfect symmetry of the original atoms, and also the simple but different symmetry of the water molecules themselves.
Approximately 70 per cent of Earth’s surface is covered by water. At the El Tatio Geysers you can see water in all its three forms. Walking through pools of water on the ground, I held a sheet of glass in the geysers’ steam and watched ice crystals form on it.
Exactly like the journey of steam to ice, of chaos to order, this was the Universe in transition. A transition where the structure and substance of all the particles of matter emerged for the first time.
The important point here is that all this complexity emerged when the symmetry was broken, but we did nothing to the water itself to break its symmetry other than cool it down. So although it looks for all the world as if a master sculptor sat down and chiselled out beautiful patterns in the ice, this intricacy and beauty emerged completely spontaneously out of building blocks that are themselves utterly symmetric.
Physicists call this process spontaneous symmetry breaking, and it is this idea that lies at the heart of our understanding of the early Universe
THE BIG BANG
Thirteen billion years ago the Universe began in the event called the Big Bang. We don’t know why. We also don’t know why it took the initial form that it did. This is one of the unsolved mysteries that makes fundamental physics so exciting. The first milestone we can speak of in anything resembling scientific language is known as the Planck Era, a period that occurred a mind-blowing 10–43 seconds after the Big Bang. When written in full, that number has 42 decimal places: 0.00000000000000000000000 0000000000000000001 seconds. That’s not very long at all. This number can be arrived at very simply because it is related to the strength of the gravitational force. It is so incredibly tiny ultimately because gravity is so weak – and we don’t know the reason for that, either! At that time the four fundamental forces of nature that we know of today – gravity, the strong and weak nuclear forces, and electromagnetism – were one and the same force, a single ‘superforce’. There was no matter at this stage, only energy and the superforce. This is what a physicist would call a very symmetric situation.
As the Universe rapidly expanded and cooled it underwent a series of symmetry-breaking events. The first, at the end of the Planck Era, saw gravity separate from the other forces of nature, and so the perfect symmetry was broken. Around 10–36 seconds after the Big Bang, another symmetry-breaking event occurred which marked the end of the Grand Unification Era. This saw the strong nuclear force (the force that sticks the quarks together inside protons and neutrons) split from the other forces. At this point the Universe underwent an astonishingly violent expansion known as inflation, in which the Universe expanded in size by a factor of 1026 (that’s 100 million million million million times) in an unimaginably small space of time – it was all over in 10–32 seconds. This was when sub-atomic particles entered the Universe for the first time, but they weren’t quite what we see today because none of them had any mass at all.
Careful scientific study leads us to conclude that the building blocks of our Universe are fundamentally hydrogen and helium.
Up until this point this story is theoretically well-motivated but experimentally relatively untested. The next great symmetry-breaking event, however, which occurred 10–11 seconds after the Big Bang, is absolutely within our reach because this is the era we are recreating and observing at CERN’s Large Hadron Collider. It is called electroweak symmetry breaking; at this point the final two forces of nature – electromagnetism and the weak nuclear force – are separated. During this process the sub-atomic building blocks of everything we see today (the quarks and electrons) acquired mass. The most popular theory for this process is known as the Higgs mechanism, and the search for the associated Higgs Particle is one of the key goals of the Large Hadron Collider project.
We are now on very firm experimental and theoretical ground. From this point on we know pretty much exactly what happened in the Universe because we can do experiments at particle accelerators to check that we understand the physics. The emergence of the familiar particles and forces we see in the Universe today happened, we believe, as a result of a series of symmetry-breaking events which began way back at the end of the Planck Era. The concept of spontaneous symmetry breaking in the early Universe is exactly the same as for the transitions from water vapour to liquid water to ice. Complex patterns emerge without prompting – just as a result of falling temperature – and these patterns obscure the underlying symmetry of the initial state. So just as the seemingly infinite complexity of snowflakes masks the simple symmetry of oxygen and hydrogen atoms, so the array of forces of nature and sub-atomic particles we see as the building blocks of the Universe today obscures the symmetry of the early Universe.
There is now one final step needed to arrive at the protons and neutrons – the building blocks of the elements – and the first elements themselves. This began around a millionth of a second after the Big Bang, when the quarks had cooled enough to become glued together by the strong nuclear force to form protons and neutrons. The simplest element, hydrogen, consists of a single proton. So after only a millionth of a second in the life of the Universe, the first chemical element had made an appearance. After three minutes, the Universe was cold enough for the protons and neutrons themselves to stick together to form helium. With two protons and one or two neutrons in its nucleus, helium is the second-simplest chemical element. There were also very, very small amounts of lithium, with three protons, and beryllium, with four protons – the third-and fourth-simplest elements. And this is pretty much where the process stopped. After three minutes the Universe had the four distinct forces we know of today – gravity, the strong and weak nuclear forces, and electromagnetism, and was composed of roughly 75 per cent hydrogen (by mass) and 25 per cent helium. This is the story of the creation of the simplest chemical elements and of successive symmetry-breaking events in the early Universe
A computer simulation of an event showing the decay of Higgs Bosen producing four muons (white tracks). This image shows how the Higgs Bosen might be seen in the CMS detector from the Large Hadron Collider at CERN.
CERN / SCIENCE PHOTO LIBRARY
Our understanding of the structure of matter has increased in the last century. Originally, atoms were thought to be the basic building blocks of life, but Rutherford’s famous diffraction experiment proved that matter consisted mainly of space, with each atom containing a very small dense nucleus surrounded by a cloud of electrons. Further investigation showed that each nucleus was composed of protons and neutrons and that each proton was composed of up and down quarks. We have now reached what is believed to be the smallest particles possible – scientists have now discovered that all matter is composed of 9 particles and 4 forces, plus the hypothetical Higgs Boson. The search for the basic building blocks of matter has used matter colliders, which can produce the very high energies that are required to recreate the temperatures in the early Universe, when these sub-atomic particles originally existed.
Nathalie Lees © HarperCollins
TIMELINE OF THE UNIVERSE: THE BIG BANG TO THE PRESENT
The history of the Universe can be split into several phases, according to the physical conditions that existed at the time. Things happened quickly in the first fractions of a second, when the Universe was filled with an intensely hot soup of energy and exotic particles. From this emerged the first protons and neutrons which were later to form the nuclei of the first atoms – mostly hydrogen and helium. After the emission of the cosmic microwave background, around 400,000 years after the Big Bang, the pace of events became more sedate. According to current understanding, the Universe will continue to expand forever, eventually fading into darkness in the unimaginably distant future.
Nathalie Lees © HarperCollins
The construction of all the chemical elements in the Universe can be illustrated with the most basic demonstration – so simple, it’s child’s play. To understand how the structure has emerged, all you need is a pot of bubble mixture. Blow one bubble and you have returned to the beginning of time, when all that existed in the Universe was the proton.
There’s a mystery at the heart of science for which, as yet, we have no explanation, and that is that this universe is simple. Underlying all of the astonishing complexity appears to be a magnificent simplicity, and nowhere is that simplicity more obvious than in the construction of the elements.
MATTER BY NUMBERS
Throughout human history the discovery and use of specific chemical elements has been intricately linked with the rise of civilisation. It is believed that copper was first mined and crafted by humans 11,000 years ago, and the specific characteristics of this metal ushered in a new age of technology and the transition from stone tools and weapons to metal ones. Four thousand years later it happened again but with iron which, even today, when mixed with carbon to form the alloy steel is the exoskeleton of industrial civilisation.
These two elements played a role in our history because of their particular physical characteristics. Copper was almost certainly the first metal to be used by humans; as it is such an unreactive chemical that it is one of the few metals that occurs naturally in its pure state. It is also very soft and malleable and so relatively easy to work into tools and weapons. When combined with another metallic element – tin – copper forms the alloy bronze; when combined with zinc it forms brass. Iron is, perhaps surprisingly, the most abundant element on Earth, and the fourth-most abundant element in the rocks of Earth’s crust. Although more difficult to extract and work with than bronze, iron is an excellent material for weapons manufacture as it is harder and lasts longer than bronze.
These two metals have had a profound influence on human history and sit just a couple of spaces apart in the periodic table. Iron (Fe) is element number 26 and copper (Cu) is at 29. The first humans to use these metals would, of course, have had no idea of the reason for the physical similarities and differences between the two elements. So what is the fundamental difference between them? The answer is remarkably simple. As described earlier, the atoms of each element are composed of three building blocks: protons, neutrons and electrons. We do not need to consider the quarks inside the protons and neutrons, because at the temperatures we encounter on Earth they stay locked away. So when discussing Earthly chemistry, we can ignore them.
THE SIX LIGHTEST ELEMENTS IN NATURE: HYDROGEN TO CARBON In each element the number of protons (p) in its nucleus is the same as the number of orbiting electrons, but the number of neutrons (n), which have no electric charge, can vary.
We have already encountered the first four elements; one of these, hydrogen, has an atomic nucleus consisting of a single proton. The proton has a positive electric charge, which allows it to trap an electron in orbit around it to form a hydrogen atom. The electron carries a negative electric charge, equal and opposite to that of the proton. This means that hydrogen atoms are electrically neutral. The reason why the electron has exactly the equal and opposite charge of the proton is not known. This is even more surprising when you look at the quarks that build up the proton. The proton is made up of three quarks – two up quarks and one down quark. The up quark has an electric charge of +2/3, and the down quark has a charge of -1/3. The electron has a charge of -1. So it is only when they are combined to form a proton that everything balances out properly. The neutron consists of two down quarks and an up, which means that it has no electric charge at all. This cannot be a coincidence, and it is one of the great challenges for twenty-first-century physics to explain it.
Chemical elements differ because of varying numbers of protons in their atomic nucleus, but the number of neutrons makes no difference to their chemical properties. Chemistry is down to the way the electrons behave that orbit around the nucleus, and the number of electrons is equal to the number of protons. As we know, the hydrogen atom consists of one proton and one electron, but there is another form of hydrogen called deuterium. Deuterium has a neutron attached to the proton inside its nucleus, but this doesn’t change its chemical properties as there is still only one electron. Technically speaking, deuterium and hydrogen are two different isotopes of the same element. Helium atoms always have two protons and two electrons; it also has forms with one and two neutrons, known as helium-3 and helium-4 respectively. Next comes lithium, with three protons, three electrons and either three or four neutrons, sometimes more. Carbon has six protons and varying numbers of neutrons, and so on. The rule is that each successive element has one more proton in its nucleus, and at least one more neutron, although the number of neutrons varies. The neutrons help the nucleus to stick together; which is bound tightly by the strong nuclear force, and neutrons add to this, even though they have no electric charge. Electric charge is a bad thing for the nucleus; because the protons are positively charged, they repel each other and try to blow the nucleus apart. The neutrons don’t suffer from this problem, which is one of the reasons why heavier nuclei tend to have more neutrons than protons.
So the construction of chemical elements is simple. If you want to turn iron into copper, add three protons and a handful of neutrons to its nucleus. That’s all there is to it. This is easier said than done, of course, yet nature can do it because when the Universe was only a few minutes old the first four chemical elements existed. The building blocks were present, but the heavier elements were assembled later
THE MOST POWERFUL EXPLOSION ON EARTH
The now iconic image of a hydrogen bomb explosion. This mushroom cloud was produced by the detonation of XX-33 Romeo on 26 March 1954; it was the third-largest test ever detonated by the USA.
US DEPARTMENT OF ENERGY / SCIENCE PHOTO LIBRARY
Years before the Manhattan project designed and delivered the most destructive weapon used in anger in the history of warfare, two of the greatest physicists of the age had already lost interest in the idea. Edward Teller and Enrico Fermi were friends and colleagues who would both go on to be members of the Manhattan team, but in 1941, before any type of nuclear bomb had been assembled, their minds were already wandering beyond the bomb that would later be dropped on Hiroshima and Nagasaki with devastating effect.
The Hiroshima and Nagasaki bombs were fission bombs, which work by splitting the nuclei of very heavy elements (uranium in the case of the Hiroshima bomb and plutonium for the Nagasaki bomb), into lighter elements such as strontium and caesium. This is the assembly of the elements in reverse. Each time a nucleus of uranium or plutonium splits, neutrons are released which trigger the splitting of other nuclei. In this way a nuclear chain reaction ensues. Each time a heavy nucleus splits, a large amount of energy is liberated – this ‘nuclear binding energy’ is stored in the strong nuclear force field that sticks the protons and neutrons together inside the nucleus.
However, even in the very early stages of the Manhattan project, years before the idea of a fission bomb was a physical reality, Enrico Fermi postulated that there was the very real possibility of creating a far more powerful type of bomb. Edward Teller became obsessed with his friend’s idea and spent the next decade designing and building a device that would create the most powerful explosions ever made on Earth. It earned Teller the title ‘father of the hydrogen bomb’.
On 1 November 1952, the fruits of Fermi’s conversation with Teller were realised. Ivy Mike was the codename given to the first successful testing of a hydrogen bomb on Enewetak, an atoll in the Pacific Ocean. The explosion was estimated to be 450 times more powerful than the bomb dropped on Nagasaki, producing a fireball over five kilometres (three miles) wide, a crater two kilometres (one mile) wide and wiping the tiny atoll off the map. Teller had collaborated with another Manhattan scientist, Stanislaw Ulam, to design the bomb, but he wasn’t present for the explosion. Instead he sat watching a seismometer thousands of miles away in his office in Berkeley, California. The explosion was so powerful that he was able to clearly see the shockwave from the comfort of his office. ‘It’s a boy!’, he cryptically told his colleagues to inform them of the success.
The Ivy Mike test was the first man-made nuclear fusion reaction. Nuclear fusion is the direct opposite of fission; it is the process by which two atomic nuclei are fused to form a single heavier element. The hydrogen bomb reproduces the process that occurred in the first seconds of the evolution of the Universe – the assembly of hydrogen into helium.
The Teller–Ulam design for the hydrogen bomb that exploded on Enewetak is the basic design employed by all five of the major nuclear weapon states today. Although the fusion element of the design is only part of its explosive power, combined with the other stages contained within the bomb it creates destruction on an unparalleled scale.
Here are two completely different ways of creating new elements and releasing vast amounts of energy. The first, fission, involves taking a heavy element and splitting it. The second, fusion, involves taking lighter elements and sticking them together. But how can both these processes result in energy being released? Isn’t there a contradiction here? There isn’t, of course, because this is how nature works. It’s all down to the delicate balance between the electric repulsion of the protons in the nucleus and the power of the strong nuclear force to stick the protons and neutrons together. Since there are two competing forces, one trying to blow the nucleus apart and one trying to glue it together, you might think there must be some kind of balancing point – an ideal mixture of protons and neutrons that is perfectly poised between attraction and repulsion. There are in fact two elements that are very close to the mixture of optimal stability, and these are iron and nickel. Elements lighter than these can be made more stable, releasing energy in the process, by fusing them together. Elements heavier than these can be made more stable, releasing energy in the process, by breaking them apart.
Look up into a clear blue sky and you are bathing in the energy of nuclear explosions on an unimaginable scale.
To be completely accurate, we should mention that there are other factors than just the balance between the electromagnetic and nuclear forces that feed into the stability of the elements. These are to do with the shape of the nucleus itself and that the balance between protons and neutrons is favoured for quantum mechanical reasons. (If you are interested, google ‘Semi-empirical mass formula’ and enjoy!)
Here on Earth, fusion may seem the ultimate human technological achievement but actually it’s the most natural thing in the world. It didn’t only happen at the Big Bang; it’s a process that can be found occurring across the Universe as we speak. In fact, it illuminates the whole Universe and happens all the time millions of miles above our heads.
Fusion is the process that powers every star in the heavens, including our sun. Look up into a clear blue sky and you are bathing in the energy of nuclear explosions on an unimaginable scale. Deep in the Sun’s core, 800,000 kilometres (500,000 miles) below the surface (where temperatures reach fifteen million degrees Celsius), the Sun is busy fusing hydrogen into helium at a furious rate. In just one second the Sun converts 600 million tonnes of hydrogen into helium, releasing as much energy as the human race will use in the next million years. This is the energy that makes the stars shine and fills the Solar System with heat and light.
The shining Sun is one of the most natural demonstrations of the effect of fusion. It, and all the other stars in the heavens, are powered by the fusing of hydrogen and helium.
It is the process of turning hydrogen into helium that creates the energy that allows all life on Earth to exist, but for all its power the Sun only converts hydrogen, the simplest element, into helium, the next simplest. This process is repeated across the night sky; every star in the Universe began its life fuelled by hydrogen and powered by this reaction.
So the assembly of the second-simplest element, helium, is well understood. We know the stars can do it, we know it happened in the very early Universe, and we can even do it ourselves on Earth. But this doesn’t help to explain the origin of the other ninety-two naturally occurring elements. Clearly, somewhere in the Universe there must be a plentiful source of the other elements because they are everywhere, our whole planet is made from them. We are made of billions and billions of atoms; from magnesium, to zinc, to iron and, of course, the one atom that life is more dependent on than any other – carbon. Every human being on the planet is made from about a billion billion billion carbon atoms. That’s an unimaginable number of carbon atoms that simply didn’t exist in the early moments of the Universe. Where did they come from? The answer must be nuclear fusion, and the natural place to look is within the stars themselves
FROM BIG BANG TO SUNSHINE: THE FIRST STARS
The first stars formed around 100 million years after the Big Bang. The rate at which they burned their hydrogen fuel essentially depends on their mass. The more massive the star, the brighter it shines and the shorter its lifetime. The key to understanding how the heavier elements came into being lies in what happens to stars when they have exhausted their hydrogen fuel. For the most massive known stars, this may take only a few million years. For stars like our sun, it may take ten billion years – but the Universe has been around for plenty of time to allow generations of stars to live and die.
The brightly shining constellation of Orion is clearly visible as it sets in the night sky.
© Tony Hallas/Science Faction/Corbis
As a star exhausts its hydrogen stores you might expect it to slowly flicker away, but for stars like our sun, the opposite happens. Having spent millions or billions of years with the core as its beating heart, a star that is running out of hydrogen in fact swells up to potentially hundreds of times its original size. Such stars are known as red giants.
One of the closest red giants to Earth is the star Alpha Orionis, better known as Betelgeuse, the ninth-brightest star in our night sky and one of our nearest neighbours in cosmic terms, a mere 500 light years away. Betelgeuse has long been familiar to stargazers, notable for its brightness and reddish tinge that is clearly visible to the naked eye. Sir John Herschel studied the star intensely in the nineteenth century, recording the dramatic variations in its brightness. However, it was only when three astronomers from the Mount Wilson Observatory in California tried to measure its diameter that we realised this was no ordinary star. Albert Michelson, Francis Pease and John Anderson used a specially designed telescope to measure the scale of this red star using a technique known as interferometry. By measuring the angular diameter (the apparent size of an object from our position on Earth), they came up with a number that, although it’s been refined since, revealed something profound: Betelgeuse is a true giant in every sense. This star is about twenty times the mass of our sun but its size is rather more impressive. If you put Betelgeuse at the centre of our solar system it would dwarf our sun. In fact, Betelgeuse would extend past the Earth’s orbit, encompassing everything out to Jupiter. Current estimates suggest it is around 800 million kilometres (500 million miles) in diameter; a vast, ethereal wonder that would fill our solar system with a single wispy star.
Betelgeuse is a vast wonder that would fill our solar system with a single wispy star.
Due to its immense size and relative proximity, we can study Betelgeuse in incredible detail. In 1996, the Hubble Space Telescope took a picture of Betelgeuse that was the first direct image of another star to reveal its disc and surface features. We’ve even imaged sunspots on its surface and been able to study its atmosphere in ever-increasing detail. However, it’s not the surface of the red giant that holds the clue to where the heavy elements are made; to understand that, we need to journey deep into its dying heart
These images of Betelgeuse are based on pictures taken by the Very Large Telescope at the European Southern Observatory, in Chile, and show gas plumes bursting from the star’s surface into space.
Betelgeuse is the ninth-brightest star in our galaxy and one of our nearest neighbours. It can be seen from Earth with the naked eye – easily identifiable in the night sky for its brightness and reddish tinge.
When making a television documentary, you are always looking for visual ways to tell complex stories. While filming Wonders of the Universe, we journeyed all over the world in search of analogies and backdrops, but for me the most successful of all was an abandoned prison in the heart of Rio de Janeiro, Brazil.
The building itself was a gutted husk, a brick skeleton; all the windows, if it ever had them, were gone. The cells were dormitories of twenty or thirty concrete bunk beds in close rows. Each had a single tiny bathroom, some with ragged pieces of cloth still draped across the entrance, paying lip service to privacy. The walls of the cells were a grotesque patchwork of ripped colour, papered with glamour girls mixed with the odd football team. I found it disturbing for two reasons. First, you can’t stop wondering about incarceration there; the centre of a hot, humid city like Rio is not the place to spend years inside a steel and concrete cage. The second was less cerebral: the prison was wired with live explosives. From inside the shell the bright outside pressed and glowed like a stellar surface, impossible to view against the internal black. The light won’t come in. It stays outside in the city. I could feel the analogy as I descended down holed, cement-dusted precarious stairwells into the dense heart of the dying star. It is here, inside a violent, condemned structure, far from the light of the surface, that the elements of living things are meticulously assembled. In here, the star transforms from matter consumer to matter producer.
Stars exist in an uneasy equilibrium. Their gravity acts to compress them, which heats them up until the electromagnetic repulsion between the hydrogen atoms is overcome and they fuse together to make helium. This releases energy, which keeps the star up. When the hydrogen runs out, the outward pressure disappears; gravity regains the upper hand and the structure of the star changes dramatically. The core collapses rapidly, leaving a shell of hydrogen and helium behind. Within the shrinking core the temperature rises until, at 100 million degrees Celsius, a new fusion process is triggered. At these temperatures helium nuclei can overcome their mutual electromagnetic repulsion and wander close enough together to fuse – the star begins to burn helium. This transfer from hydrogen to helium fusion has two profound effects: firstly, sufficient energy is released to halt the stellar collapse, so the star stabilises and rapidly swells. This is the beginning of its life as a red giant. Secondly, it fuses into existence the element vital for life. At first sight the fusion of two helium nuclei, each consisting of two protons and two neutrons, should only be able to produce the isotope beryllium-8, composed of four protons and four neutrons. This is an unstable isotope of beryllium that quickly breaks down, but in the intense temperatures of a dying star, as the core exceeds 100 million Kelvin, these nuclei live just long enough to fuse with a third helium nucleus, creating the precious element carbon-12. This is where all the carbon in the Universe comes from; every carbon atom in every living thing on the planet was produced in the heart of a dying star.
Just as in a dying star, the structure of a building and the elements that keep it standing become unstable over time. This prison was given a helping hand to its destruction, but a dying star will detonate itself as it reaches the end of its life, producing spectacular planetary nebulae. It took seconds to demolish the prison block, which is the same length of time it takes for a red giant star to collapse.
The helium-burning phase doesn’t end with the alchemic synthesis of carbon, because during the same intensely hot phase in the star’s life the conditions allow a nucleus of helium to latch onto a newly minted carbon nucleus to create another element vital for life. Oxygen makes up 21 per cent of the air we breathe, is a prerequisite for water, the solvent of life, and is the third-most common element in the Universe after hydrogen and helium. As you breathe in around two and a half grams of oxygen each minute, it’s worth remembering that all this life-giving gas was created in an environment as far away from our understanding of what is habitable as you can get.
Compared with the lifetime of a star, this stellar production line of carbon and oxygen is over in the blink of an eye. Within about a million years the helium supply in the core is used up, and for many stars that’s where fusion stops. Any average-sized star, like our sun, has by now reached the end of its productive life. When our sun reaches this stage, in about ten billion years’ time, there won’t be enough gravitational energy to compress the core any further and restart fusion. Instead, the star becomes more and more unstable, huge pressure points will build up, until eventually the whole stellar atmosphere explodes, hurling the precious cargo of oxygen, carbon, hydrogen, and all, on its journey into space. For at this brief moment in time, no more than a few tens of thousands of years, a dying star will create one of the most beautiful structures in our universe: a planetary nebula.
Once this brief cosmic light show is over, an average-sized star will shrink to an object no bigger than Earth. A white dwarf is the fate of such stars and billions like it, but for massive stars like Betelgeuse the action is far from over. If a star has a mass half as big again as our Sun, it will continue down the chemical production line. As helium fusion slowly comes to an end, gravity takes over and the collapse of the core restarts. The temperature rises, launching the third stage in the birth of our universe’s elements, and with temperatures reaching hundreds of millions of Kelvin, carbon fuses with helium to make neon, neon fuses with more helium to make magnesium, and two carbon atoms fuse to make sodium. With more and more elemental ingredients entering the cooking pot, and temperatures rising, the heavier elements are produced one after another. The core continues to collapse, the temperature continues to rise, and the next stage of fusion begins, leaving layers of newly minted elements behind.
With the first twenty-five elements now created within the star, the runaway production line hits a block at the twenty-sixth element, iron, created from a complex cascade of fusion reactions fuelled by silicon. At this stage the temperature of the star is at least 2.5 billion Kelvin, but it has nowhere else to go. The peak of nuclear stability has been reached, and no more energy can be released by adding more protons or neutrons to iron. The final stage of iron production lasts only a couple of days, transforming the heart of the star into almost pure iron in a desperate bid to release every last gasp of nuclear binding energy and stave off gravity. This is where the fusion process stops; once the star’s core has been fused into iron, it has only seconds left to live. Gravity must now win, and the star collapses under its own weight forming a planetary nebula.
As I walked away from the prison for the cameras, a button was pressed and the building fell. The demolition took seconds – the same time it takes a red giant star like Betelgeuse to collapse
This dying star, IC 4406, like many planetary nebulae, is highly symmetrical. It is known as the ‘Retina Nebula’ because the tendrils of dust emitted from it that have been compared to the eye’s retina.
About 5,000 light years (4,700 trillion kilometres/2,900 trillion miles) from Earth lies the Calabash Nebula. This image, captured by the Hubble Space Telescope, shows material being ejected from the star.
The Eskimo Nebula is so-called because of its resemblance to a head surrounded by fur-lined hood when viewed from Earth. It was discovered in 1787 by astronomer William Herschel.
This composite image depicts the Helix Nebula. This planetary nebula resembles a doughnut, as seen from Earth, but new evidence suggests that the Helix in fact consists of two gaseous discs.
MyCn18 is a young planetary nebula which was discovered in the early twentieth century. However, it was this Hubble Telescope image in January 1996 that revealed the nebula’s hourglass shape with intricate engravings.
The aptly named Cat’s Eye Nebula (officially known as NGC 6543) was one of the first planetary nebulae to be discovered (in 1786 by William Herschel). It is one of the most complex nebulae known to exist in the Universe.
Imaged on 20 July 1997, Mz3 has been dubbed the Ant Nebula because its outline resembles the head and thorax of an ant when seen through telescopes on Earth. On close inspection, the ant’s body appears to consist of two fiery lobes.
This planetary nebula is known as Kohoutek 4-55 (or K 4-55), named after its discoverer, Czech astronomer Lubos Kohoutek. It is unusual for its multi-shell structure.
THE RAREST OF ALL
Once the centre of the great American gold rush, the 16-1 mine is one of the few gold mines still operating in the state of California today. Digging for gold there with the miners was an enlightening experience. As I peered at seemingly ordinary rocks, I could see glints and glimmers of a familiar yellow colouring, revealing the stones’ precious hidden cargo of gold.
The first twenty-six of the elements are forged in the cores of stars and are distributed through the Universe in their inevitable collapse. But what of the other seventy-two – some of which are vital for life, and many of which we hold most precious? If they are not formed within stellar furnaces, what could their origin possibly be?
In the remote forests of northwestern California, the mountains still hide a secret that made the quiet pine woods the ultimate destination for fortune seekers only a century ago. Although they’re empty today, in the late nineteenth century this was the centre of the California gold rush. Hundreds of thousands of people arrived here, trying anything and everything to get rich, from simple panning to the most advanced mining techniques available. Gold worth billions of dollars was extracted, fuelling the rise of one of the world’s great cities, San Francisco. The insatiable appetite for gold has waned today, but in the forests around Lake Tahoe, the 16–1 mine remains one of the few gold mines still operating in the state of California.
For almost 100 years, miners have been digging for gold in the 16–1, and it is still one of the richest gold deposits in the world, due to a quirk in the local geology. The unique thing about California is that it sits on the divide between the North American tectonic plate and the Pacific tectonic plate. The whole region is one enormous fault line, with thousands of smaller faults running through the rocks of the mountains. When you travel into the mine, which is nothing more than a series of horizontal tunnels at gentle gradients hollowed out of the mountainside, you can see these fault lines everywhere; they reveal their presence as visible boundaries between rock and quartz – a maze of mini-faults. One hundred and forty million years ago, in the Jurassic period when the dinosaurs were running around above the mine, hot water bubbled up and flowed through this rock, carrying a precious cargo. Its water was laden with gold brought up from deep within the Earth, deposited through the seams of quartz. For the last 100 years all the miners have had to do is to follow quartz seams laced with shimmering gold.
The gold that runs all the way through the quartz in the 16–1 mine is unusually pure, at anything up to 85 per cent, and the thick tendrils snaking through the rock glint and glimmer that familiar yellow in the sunlight. The rest is about 14.5 per cent silver, with traces of heavier metals. The area is so rich in gold that it can even be found as simple pure nuggets that can be picked up off river beds, and at the 2010 price of around £900 per troy ounce, it’s obvious why mines like this are still in operation.
If you stop to think about it though, there’s something a bit odd about the value we attach to gold. Throughout history people have gone to extraordinary lengths to get their hands on it, which is odd because it isn’t particularly useful for anything. Copper and iron will help you survive, but gold is next to useless. Most of the gold that we’ve struggled to extract has ended up as jewellery. The only thing that gold has going for it, other than being shiny, is that it is incredibly rare, and this is what drives up its price. All the gold dug out of the ground throughout all of human history – with all the associated tragedy and elation, hardship and riches – would just about fill three Olympic-sized swimming pools.
All the gold dug out of the ground throughout all of human history would just about fill three Olympic-sized swimming pools. It is this almost vanishing scarcity that makes gold so valuable.
It is this almost vanishing scarcity (three swimming pools relative to the size of a planet) that makes gold so valuable; it is just one of many rare elements that are to be found in the most minute of traces within the Earth.
There are over sixty elements heavier than iron in the Universe, some are valuable, such as gold, silver and platinum; some are vital for life, such as copper and zinc; and some are just useful, such as uranium, tin and lead. Very massive stars can produce very tiny amounts of the heavier elements up to bismuth-209 (element number 89) in their cores by a process called neutron capture, but it is known that this makes nowhere near enough to account for the abundances we observe today. There simply haven’t been enough massive stars in the Universe.
The conditions necessary to produce large amounts of the elements beyond iron are only found in the most rare of all celestial events. Blink and you’ll miss them, because in a galaxy of 100 billion stars the conditions violent enough to form substantial amounts of these elements will exist on average for less than two minutes in every century
SUPERNOVA: LIFE CYCLE OF A STAR
All stars are born from clouds of gas, but the length of their life and their eventual fate are governed by their mass (i.e. how much gas they contain). Stars dozens of times heavier than the Sun live for only a few million years before swelling into supergiants and exploding as supernovae (top row). However, stars like the Sun live longer and die more gently, shining steadily for billions of years before swelling into red giants and losing their outer layers as a planetary nebula (middle row). The core of the star, exposed as a white dwarf, then continues to glow for billions of years more before gradually fading out. The least massive stars, the red dwarfs (bottom), simply fade out over tens of billions of years.
Nathalie Lees © HarperCollins
THE BEGINNING AND THE END
This computer-generated sequence of images shows what will happen when Betelgeuse goes supernova. Deep in the heart of the star, the core will succumb to gravity and fall in on itself, then rebound with colossal force. The blast wave emitted generates the highest temperatures in the Universe. Over millions of years the scattered elements of the exploded star will become a nebula, at the heart of which is a super-dense core that is Betelgeuse the neutron star.
After a few million years of life, the destiny of the largest stars in our universe is a dramatic one. Having run out of hydrogen and burnt through the elements all the way to iron, giant stars teeter on the edge of collapse. Yet even in this dilapidated state these stars have one last violent act, and it is a generous one. It occurs with such intensity that it allows for the creation of the heavy elements.
If we could gaze deep into the heart of one of these dying giants, we would see the core finally succumb to gravity. As fusion grinds to a halt, this giant ball of iron falls in on itself with enormous speed, contracting at up to a quarter of the speed of light. This dramatic collapse causes a rapid increase in temperature and density as the core shrinks to a fraction of its original size. The inner core may eventually shrink to 30 kilometres (19 miles) in diameter. At this point, with temperatures nearing 100 billion Kelvin and densities comparable to those inside an atomic nucleus, quantum mechanics steps in to abruptly halt the collapse. By now most of the electrons and protons in the core have been literally forced to merge together into neutrons. Neutrons, in common with protons and electrons, obey something called the Pauli exclusion principle, which effectively prevents them from getting too close to one another (in more technical terms, no two neutrons can be in the same quantum state). This has the effect of making a ball of neutrons the most rigid material in the Universe – 100 million million million times as hard as a diamond. When the neutrons can be compressed no more, the contraction must stop and all the superheated collapsing matter rebounds with colossal force. A shockwave shoots out through the star and as this blast wave runs into the outer layers of the star it generates the highest temperatures in the Universe – 100 billion degrees. The precise mechanism for this rapid heating is not fully understood, but it is known that for a matter of seconds the conditions are intense enough to form all the heaviest elements we see in our universe, from gold to plutonium. This is a Type II supernova – the most powerful explosion we know of.
Supernovae are so rare that since the birth of modern science we have never had the chance to see one close up. The last supernova explosion seen from Earth in our galaxy was in 1604, a few years before the invention of the astronomical telescope. On average, it is expected there should be around one supernova explosion in the Milky Way per century, but for the last 400 years we’ve had no luck. It’s long overdue and astronomers are always searching the skies for stars which they think might be the most likely candidate to go supernova.
One of the prime candidates is Orion’s shining red jewel, Betelgeuse. With so many telescopes trained on this nearby star, we have been able to follow its every move for decades. Charting its brightness, we have discovered that it is extremely unstable; it has dimmed by about 15 per cent in the past decade. As supernova candidates go, Betelgeuse is top of the list. It is generally thought that Betelgeuse could go supernova at any time. It is a relatively young star, perhaps only ten million years old, and has sped through its life cycle so rapidly because it is so massive. However, when you’re ten million years old, the end of your life can be quite drawn out and a phrase like ‘any time soon’ in stellar terms is not quite what you might expect. It means that Betelgeuse should go supernova at some point in the next million years, but equally it could explode tomorrow. What we do know is that when it does go it will provide us with quite a show. Betelgeuse is only 500 light years away, almost uncomfortably close, which means that the explosion will be incredibly bright. It will be by far the brightest star in the sky and it may even shine as brightly as a full moon at night and fill the sky as a second sun during the day.
The giant Orion Molecular Cloud is an extensive area of star formation about 1,500 light years from us, centred on the impressive Orion Nebula. This infrared image of it, from NASA’s Spitzer Space Telescope, shows light from newborn stars within the Orion Nebula. The nebula can be seen from Earth with the naked eye as a hazy ‘star’ in Orion’s sword.
This computer-generated image shows just how bright scientists believe the heavens will be once Betelguese has gone supernova; it will flood the skies with light – day and night.
When stars are more massive than about eight times the Sun, they end their lives in a spectacular explosion. The outer layers of the star are hurtled out into space at thousands of miles an hour, leaving a debris field of gas and dust. Where the star once was, a small, dense object called a neutron star is often found. While around only 16 kilometres (10 miles) across, the tightly packed neutrons it contains have more mass than the entire Sun. The bright blue dot in the centre of this X-ray image of RCW 103 is believed to show the neutron star that formed when the star exploded in a supernova 2,000 years ago.
In a single instant, Betelgeuse will release more energy than our sun will produce in its entire lifetime. As the explosion tears the star apart, it will fling out into space all the elements the star has created through its life.
Over millions of years these newly minted elements will spread out to become a nebula, a rich chemical cloud drifting in space. At the heart of it, all that will remain will be the super-dense core of neutrons; the remnants of the star that was once a billion miles across will have been squashed out of all recognition by gravity. This is a neutron star, the ultimate destiny of Betelgeuse; a dense, hot ball of matter which is the same mass as our Sun but only 30 kilometres (19 miles) across.
We may not have seen neutron stars close up, but we have seen them from afar. X-ray images have been taken that give us vital information about these stars, in particular recent pictures of RCW 103, the two-thousand-year-old remnant of a supernova explosion that occurred about 10,000 light years from Earth (see left).
When Betelgeuse explodes it will be incredibly bright. It will be by far the brightest star in the sky and it may even shine as brightly as a full moon at night and fill the sky as a second sun during the day.
This may sound like a cosmic graveyard, but it is in the deaths of old stars that new stars are born. This is the Earthly cycle of death and rebirth played out on a cosmic scale. We can see that beautiful cycle happening today in the constellation of Orion. In an area known as the sword handle lies the Orion Nebula. To the naked eye it appears to be a misty patch of light in the night sky, but through a telescope it is a majestic wonder of the Universe. Hidden in its clouds are bright points of light, new stars forming from the clouds of elements blown out by supernova explosions; the new born from the deaths of the old.
It is from such a cycle that we emerged – within a nebula just like this, five billion years ago, our sun was formed. Around that star a network of planets condensed from the ashes, and amongst them was Earth; a planet whose ingredients originated from the nebula, a cloud of elements formed in the deaths of stars, drifting through space.
But that’s not quite the end of the story, because it is now thought that the chemical elements themselves are not the most complex pieces of ‘us’ that were assembled in the depths of space
THE ORIGIN OF LIFE
This seemingly ordinary piece of rock is anything but; this asteroid fragment is older than any rock on Earth and is one of the thousands of meteorites that fall onto our planet every year.
There are thousands of asteroids in our solar system, mostly within an asteroid belt that formed 4,568 million years ago, and on average one meteorite falls to Earth once a month. However, each and every one discovered is hugely important, regardless of its size, as these asteroid pieces give us a real insight into what forms the building blocks of life.
At first sight the graph opposite – depicting the spectrum of the light from the Orion Nebula (taken from the Herschel Space Observatory Telescope) – looks rather uninspiring, but the information that it contains is in fact fascinating. This illustration reveals that the Orion Nebula is not just a cloud of elements; there is complex chemistry happening out there deep in space.
Just like the black lines in the spectrum of the Sun, the peaks on this graph correspond to particular chemical elements, but some of these peaks derive from complex molecules – there is water in the nebula, and sulphur dioxide. Perhaps more surprisingly, there are also complex carbon compounds – methanol, hydrogen cyanide, formaldehyde and dimethyl ether. This is direct evidence for complex carbon chemistry occurring in deep space. This is tremendously exciting because it means that we are seeing the beginnings of the chemistry of life in a vast cloud of interstellar gas.
The connection doesn’t end there; we may be connected to the chemistry out there in space even more directly. The photo opposite is of a meteorite, a piece of rock that fell to Earth from somewhere out in the depths of the Solar System. It is almost certainly older than any rock on Earth because it was formed from the primordial dust cloud, the nebula that collapsed to form the Sun and the planets five billion years ago. When looking inside this ancient rock we discovered something incredibly interesting: it was found to contain amino acids, the building blocks of proteins, which in turn are the building blocks of life. This strongly suggests there was very complex carbon chemistry happening out there in space, forming the building blocks of life, over four and a half billion years ago. It raises the intriguing prospect that the first amino acids on Earth may have formed in the depths of space and been delivered to our planet by meteorites.
ORION’S MOLECULAR MAKE-UP: This detailed spectrum, obtained by ESA’s Herschel Space Observatory, shows the fascinating chemical fingerprints of potential life-enabling organic molecules in the Orion Nebula.
The fundamental building blocks of life may have formed in the depths of space and been delivered to our planet by meteorites.
This is one more beautiful piece of evidence that forces us to think differently about those twinkling lights and smudges of gas and dust in the sky. When we look out into space we are looking at our place of birth. We truly are children of the stars, and written into every atom and molecule of our bodies is the history of the Universe, from the Big Bang to the present day
Our story is the story of the Universe. Every piece of every one and every thing you love, of every thing you hate, of every thing you hold precious, was assembled in the first few minutes of the life of the Universe, and transformed in the hearts of stars or created in their fiery deaths. When you die those pieces will be returned to the Universe in the endless cycle of death and rebirth. What a wonderful thing to be a part of that universe – and what a story. What a majestic story!
Supernovae are the long-awaited spectacles of the skies. It is in the death of old stars that new ones are born, and their demise plays a crucial part of the endless cycle of death and rebirth that occurs right across our universe.