Innholdsfortegnelse for Understanding Astrophysics i Understanding Astrophysics

Astrophysics is one of the most fascinating fields of science – studying the many wonders of the universe can help us better understand our place in it. In this brand-new special edition, we’ve compiled a selection of articles from the All About Space, How It Works, and Space.com archives to explain the science behind cosmic questions, including how galaxies form and what distant stars and planets are made of. We will also investigate some of the biggest mysteries in the cosmos, such as how the universe began and whether there is life beyond Earth.…

People have always sought out ‘big-picture’ theories that explain how the universe began, what it looks like on the largest scales and how it evolves over time. In the past, such theories were often based more on human imagination than anything else. But our present best contender, the Big Bang theory, is much better than that. It’s based on a mixture of observational evidence and a mathematical understanding of how space and matter behave on very large scales, and most astronomers believe it probably comes quite close to the truth. There are two reasons we no longer need to rely on pure imagination to visualise the evolution of the universe. First there’s the fact that we can actually see into the distant past. That’s because light travels at a finite…

A telescope is almost like a time machine, allowing us to peer back into the distant past. With the aid of Hubble, NASA has shown us galaxies as they were many billions of years ago. Hubble’s successor, the James Webb Space Telescope, has the ability to look even deeper into the past. As of April 2023, it has been able to observe galaxies from around 13.4 billion years ago, less than 350 million years after the Big Bang. And unlike Hubble, which sees mainly in the visible waveband, Webb is an infrared telescope – a big advantage when looking at very distant galaxies. The expansion of the universe means that waves emitted from them are stretched out, so light that was emitted at visible wavelengths actually reaches us in the…

A Light year is a measurement of distance and not time, as the name might suggest. A light year is the distance a beam of light travels in a single Earth year, or around 9.7 trillion kilometres (6 trillion miles). On the scale of the universe, measuring distances in kilometres or miles just doesn’t cut it. In the same way that you may measure the distance to the supermarket in the time it takes to drive there, astronomers measure the distances of stars in the time it takes for their light to travel to us. For example, the nearest star to our Sun, Proxima Centauri, is 4.2 light years away. Unlike the speed of your car when travelling on different roads or in traffic, the speed of light is constant…

1 The ‘calm’ black hole If a black hole is calmly sitting at the centre of its galaxy, it generally distorts the fabric of the universe around it. It leaves a dent in this sheet of space-time from which nothing – not even light – can escape. 2 A swirling disc of dust and gas An accretion disc made of gas and dust circles the black hole. If the black hole isn’t particularly active, then the matter won’t fall into it. 3 Heating up  When the material falls into the black hole and reaches the event horizon – the point of no return – a lot of friction is created, superheating atoms and tearing them apart. 4 The active black hole When a black hole begins spinning into motion, it…

“If the star is massive enough then the collapse will continue past the neutron star stage” 1 Birth of a massive star First you need a massive star, at least 30 to 40 times more massive than the Sun. Such stars are relatively rare, but can form alongside smaller stars. 2 Death of a massive star Massive stars use up their hydrogen fuel more quickly, after just a few million years, and when they can no longer maintain nuclear fusion in their core, they explode. 3 The stellar core implodes When fusion reactions stop, gravity causes the core to implode to form a compact neutron star, while the surrounding layers of the star rebound off the neutron star and explode as a supernova. 4 Gravitational collapse If the star, or more…

Exoplanet hunting has been dominated by NASA’s Kepler and Transiting Exoplanet Survey Satellite, which stare out at the stars looking for drops in brightness as the members of other planetary systems pass between ourselves and their parent stars. But the first exoplanets were discovered by the ‘wobble’ method, which looks for changes in starlight as the star is slowly dragged around by its accompanying planets. The difference is small, as stars are generally much larger than their collection of planets, and for multi-planet systems the motion is a combination of the influence of all partners. All the bodies involved in an orbital relationship will be influenced by each other to some degree; it’s easiest to envisage the most extreme case, two equally sized objects orbiting each other. If Earth and…

1 Main sequence This is the region where stars spend the majority of their lives – a star’s position in the main sequence is largely determined by its mass. 2 Red giants Most stars pass through this phase near the end of their lives, brightening and developing an atmosphere with a cool surface. 3 White dwarfs These hot stars are faint because of their tiny size – they are the burnt-out, slowly cooling cores of stars like our own Sun. 4 Supergiants Brilliantly luminous high-mass stars that display a variety of colours as they move back and forth across the Hertzsprung–Russell diagram.…

The Sun produces heat and light through nuclear fusion, converting hydrogen into helium. In this respect, it’s a pretty typical star. Around 90 per cent of all stars are undergoing the same process, referred to as the main sequence of the stellar life cycle. Even so, there are some striking exceptions, such as stars of very low or very high mass or ones that have exhausted all their nuclear fuel. Here we take a look at some of these extreme stars – from brown dwarfs to supergiants and from neutron stars to weird hybrid stars. But first it’s worth reviewing the basics of stellar evolution. Although the stars in the night sky look similar to the naked eye, there’s actually a wide variety of stellar types. This is partly because…

These are extremely massive young stars that have already used up most of their hydrogen fuel and are now fusing helium into heavier elements. Despite their size and luminosity, they’re actually very rare, accounting for less than one in a thousand of the stars in the galaxy. There are two reasons for this. To start with, when clusters of stars form in interstellar gas clouds, the distribution of masses is strongly biased towards low-mass stars. Secondly, high-mass stars have very short life spans – only about 10 million years compared to 10 billion or more for our Sun.…

A white dwarf represents the final stage in the evolution of a star like the Sun, following on from the comparatively brief red giant phase. During the previous phase, the core of the star was gradually shrinking and getting hotter while the outer layers expanded to enormous proportions. Eventually the core generates so much energy that it blows the outer layers off completely, leaving just the dense, hot core behind. This core is the white dwarf, which will continue to exist, gradually losing its accumulated heat, for many billions of years. Although a white dwarf is extremely dense by ordinary standards, it’s not as dense as a neutron star, where all the matter has been compressed down to neutrons. While a neutron star packs all of a star’s mass into a…

If something cast a shadow but you couldn’t see it, you’d be intrigued. If it did that on the scale of the universe, you’d be perplexed. If you then couldn’t find it despite your best efforts, you’d likely be frustrated. This is the situation that scientists looking for dark matter find themselves in. But dark matter doesn’t even cast shadows; it’s invisible to all electromagnetic radiation. And yet we have solid evidence that it exists. In fact, current calculations show that it comprises 80 per cent of all of the mass in the universe. But a 2020 study modelling dark matter as filtering through bubbles after the Big Bang may help point scientists in a new direction. Although the mystery of dark matter can be traced as far back as…

Invisible matter Scientists think that dark matter may be like ordinary matter, only invisible and non-interacting. However, we don’t know. We could be completely mistaken, and it could be something else entirely, yet to be theorised. It has a gravitational effect Like ordinary matter, its dark counterpart has a gravitationally attractive effect on its surroundings. This can be seen in the gravitational lensing of large galaxies and galaxy clusters. It was seen in the 19th century Lord Kelvin first noted the peculiar motions of stars in the Galactic Centre, concluding in 1884 that a large number of ‘unseen dark bodies’ were present and causing the gravitational effects. Voyager 1 has disproved one theory The Voyager 1 probe, now outside the Sun’s heliosphere, would have been able to detect faint radiation…

1 Finding the right stars These supernovae occur when a white dwarf is found in a binary pair with another star. 2 Matter transfer Two stars orbit close enough to each other that matter will transfer from the companion onto a white dwarf star in a process called accretion. 3 Squeezing down This accretion of matter from its companion adds extra mass. The additional gravitational forces compress the already highly pressurised core of the white dwarf. 4 A star reborn As the star approaches the Chandrasekhar limit, the dying star comes to life again and undergoes fusion in its centre. 5 Limited gains However, white dwarfs can only get so massive through accretion. The Chandrasekhar limit puts their maximum size at about 1.4 times the mass of our Sun. 6…

Have you ever wondered how different your life would be if you had made different decisions? You may never know what may have been, but incredibly, all of those ‘what if’ scenarios may have played out somewhere. Over the past few years, support for the idea that we live in a ‘multiverse’, in which our universe is just one tiny bubble among countless others, has been gaining strength in recent years. For many people, the term ‘multiverse’ conjures up pictures of parallel realities, some with just a slight difference from our own. And that sort of multiverse is indeed predicted by the ‘many worlds’ interpretation of quantum mechanics – the strange but highly successful model of how the universe works on the smallest scales – wherein every possible quantum state…

Level 1 Where an identical Earth exists The simplest multiverse is one that most certainly exists – the Big Bang model of cosmic origins predicts that every point in the universe has a ‘Hubble volume’ around it, limited by the expansion of the universe and the distance light has been able to travel in the 13.8 billion years since the infant universe became transparent. In practice, this means our Hubble volume is a sphere 93 billion light years across, but there are many more Hubble volumes extending far beyond what we can see. If the universe has a closed geometry, the number is limited as space curves back around on itself, but if the universe is open, as seems most likely, there may be an infinite number of Hubble volumes,…

“The universe as a whole is expanding” 1 Earth Earth’s diameter is 12,756 kilometres (7,926 miles). The Moon orbits Earth at an average of 384,400 kilometres (238,855 miles). 2 Solar System The outermost planet in the Solar System, Neptune, orbits the Sun at a distance of 4.5 billion kilometres (2.8 billion miles). 3 Living local Stars in our local region of space are separated by light years – tens of trillions of kilometres. The brightest star in the sky, Sirius, is 8.6 light years away. 4 Home galaxy Our Sun and Solar System, and all the stars in our sky, are members of the Milky Way – a vast spiral of stars that’s roughly 120,000 light years across. 5 Grouping up The Milky Way is a major member of a…

COBE The first space mission designed to study the CMB was NASA’s Cosmic Background Explorer, launched in 1989. It found the CMB is much more uniform across the sky than expected. WMAP A second NASA spacecraft, the Wilkinson Microwave Anisotropy Probe, mapped the CMB between 2001 and 2010, confirming the astonishing uniformity. Planck Planck was the European Space Agency’s follow on to WMAP. Operating from 2009 to 2013, it remapped the CMB with higher sensitivity and resolution than its predecessor.…

Everything in our universe originated after the Big Bang, so there are no conceivable observations we can make that would tell us anything about what happened before then. For some scientists this makes the question of what happened before the Big Bang meaningless, but for others it’s no obstacle to theoretical speculation. One of the most intriguing suggestions is the concept of eternal inflation. The current Big Bang theory requires the universe to go through an initial period of very rapid inflation, which then transitioned abruptly to the more sedate expansion we see today. But what if when our own universe dropped out of this inflationary phase it was just a tiny bubble in a vast sea of inflating space? This is the idea behind eternal inflation, which would see…

The universe is packed with galaxies. Everywhere we look we see galaxies crammed into the cosmos, grouped in clusters and great sheets that are littered throughout space-time. The most distant galaxies ever seen have been identified by the Hubble Space Telescope as being 13.4 billion light years away. Yet these are not even the most distant galactic structures out there. It’s the first galaxies that hold the record for being the furthest away from us. However, we’re yet to see them. To do so we will need the infrared prowess of the James Webb Space Telescope (JWST), which has the ability to see galaxies as they formed just 300 or 400 million years after the Big Bang – the event that threw the cosmos into existence. Understanding how galaxies form…

GIANT STAR The first generation of very massive stars, hundreds of times as massive as the Sun, would have burnt through their nuclear fuel very quickly. SEED BLACK HOLE These stars collapsed down to black holes of tens of solar masses, which then acted as seeds for the creation of much larger black holes. ACCRETION Over billions of years, gas and dust spiralling into these black holes increased their mass; this isn’t enough to explain supermassive black holes.…

Ever since humans first discovered that the stars in the night sky were bodies similar to our Sun, we’ve dreamed and speculated about the worlds that could orbit these stars. Would they be rocky terrestrial planets like Earth? Could they possess liquid water? Could the presence of this vital life-sustaining element on other worlds mean that we are not alone in the universe? “For millennia, humans have been asking the question of whether we are alone. And tied to that question, are other planets anywhere else?” Nikku Madhusudhan, a professor of astrophysics and exoplanetary science at the Institute of Astronomy of the University of Cambridge, tells All About Space. “It’s very fundamental to being human to ask the question if there are planets elsewhere.” With this considered, it’s almost shocking…

Looking up into the night sky, you might wonder just how many stars are in the universe. It’s challenging enough for an amateur astronomer to count the number of naked-eye stars that are visible, and with bigger telescopes, more stars come into view, making counting them a lengthy process. So how do astronomers figure out how many stars are in the universe? The first tricky part is trying to define what ‘universe’ means, says David Kornreich, a professor at Ithaca College in New York State. He was also the founder of the ‘Ask An Astronomer’ service at Cornell University. “I don’t know, because I don’t know if the universe is infinitely large or not,” he said. The observable universe appears to go back in time by about 13.8 billion years,…

1 Almost a star A protostar is a ball-shaped mass in the early stages of becoming a star. It’s irregularly shaped and contains dust as well as gas, formed during the collapse of a giant molecular cloud. The protostar stage in a star’s life cycle can last for a 100,000 years as it continues to heat up and become denser. 2 Star or planet? Brown dwarfs are sometimes not even considered stars at all, but instead sub-stellar bodies. They are incredibly small in relation to other types of stars, and never attained high enough temperatures, masses or enough pressure at the core for nuclear fusion to actually occur. They are below the main sequence on the Hertzsprung-Russell diagram. They have a radius about the size of Jupiter, and are sometimes…

Brown dwarfs are the smallest stars, with masses in the range of 15 to 75 times the mass of the planet Jupiter. Like an ordinary star, a brown dwarf starts life by collapsing under its own gravity from a cloud of interstellar gas, but it doesn’t have enough mass for the core temperature to rise to the point where hydrogen undergoes nuclear fusion. In other words, it never reaches the main sequence phase of stellar evolution. So why is a brown dwarf a star and not simply a very large planet? The reason is that while it’s insufficient for ordinary hydrogen fusion, the core temperature is high enough for another kind of fusion involving a scarcer isotope called deuterium. This means the brown dwarf shines, albeit very dimly, with its…

Normal atoms are composed of electrons, protons and neutrons, but if they’re squashed together forcefully enough then the protons and electrons combine to form further neutrons, and eventually that’s all that’s left. The result is one of the most extreme forms of matter known to science, and it’s what neutron stars are made of. A neutron star is one of the possible outcomes when a star finally runs out of nuclear fuel and collapses under its own gravity. Small and medium-sized stars like the Sun end up as white dwarfs, while the most massive stars become black holes. In between the two, the end result is a neutron star – an object more massive than the Sun but compressed down into a volume the size of a city. Under normal…

Most of the extreme stars we’ve listed here differ from our Sun in that they started out with lower masses, like brown dwarfs, or higher masses, like supergiants and neutron stars. The Sun’s evolution will never take it in any of those directions. On the other hand, there are two extreme phases of the stellar life cycle that do lie in the Sun’s own future: the red giant phase and the white dwarf phase. Currently the Sun is on the main sequence, converting hydrogen into helium via nuclear fusion. This phase is expected to end in about 5 billion years, after which the Sun will expand into a red giant so huge that it engulfs the planets Mercury and Venus – and possibly even Earth. The energy for this expansion,…

1 Big Bang occurs The universe begins as an extremely hot, dense state. 2 Inflation happens At 10-36 seconds the universe expands with unimaginable speed in a period known as inflation. This cools the universe further. 3 Thermal freeze out Very quickly, the subatomic particles of ordinary matter ‘freeze’ out of the dense plasma as it cools. So does dark matter. 4 Bubbles form a particle called phi starts a phase change in the universe. These act as nucleation sites, growing as expanding bubbles. 5 Filtering of matter Despite particles freezing out, they’re still hot, including dark matter. Some of the latter pass into the bubbles and gain mass. 6 Bubbles merge The bubbles merge, and the phase change completes. All the surviving dark matter particles are now part of…

Is there more than one kind? Could there be an entire family of dark matter particles as opposed to just a single type? The Standard Model of particle physics says that ordinary matter is composed of electrons as well as the quarks that make up protons and neutrons. It also includes the fundamental force-carrying particles, such as photons, gluons, bosons and some other short-lived matter particles. Could there be a similar but separate model for dark matter? Are there corresponding 'dark forces'? Forget horror and fantasy here. If there are a range of dark matter particles, could they experience their own dark matter forces? If so, could that also sometimes affect ordinary particles? This is the hope of a collaboration working with the Super Proton Synchrotron at CERN. The team…

Place your fingers on your wrist and check your pulse. You can feel the blood pumping around your body, delivering oxygen from your head to your toes. That oxygen is ferried around by trillions of red blood cells, each just 0.008 millimetres across. The element iron plays an indispensable role in this oxygen delivery, but the universe would contain very little iron if it weren’t for a ferocious type of exploding dying star called a supernova. Without supernovae, you simply wouldn’t exist. We often think of the Sun as the quintessential star, but it’s not massive enough to go supernova when it dies. According to Dr Christopher Frohmaier, a supernova researcher at the University of Southampton, to detonate in this most spectacular of celestial firework displays, a star needs a…

Under construction atop Chile’s Cerro Pachón, the Vera C. Rubin Observatory, formerly the Large Synoptic Survey Telescope, will survey a huge area of the Southern Hemisphere sky, providing data for a wide range of scientific objectives. For supernova scientists, the value of Rubin comes down to its ability to image the entire sky repeatedly every few nights, and to great depth. This means it could spot hundreds of thousands of new events. Within a minute of each change in the sky, Rubin will alert the community to respond, catching supernovae events before they fade forever. “Spectra really tell you about the underlying astrophysics, so it will unlock a wealth of information”Christopher Frohmaier 1 Large mirror Rubin’s reflecting telescope contains an 8.4-metre (28-foot) primary mirror that can track across at sufficient…

Relic radiation The CMB is the primordial ‘echo’ of the universe. Measurements taken by probes show that the universe’s geometry is nearly flat. For that to be the case, the total amount of matter in space must tally with the average density of matter to energy in the cosmos. But the CMB’s spectrum shows that this isn’t what’s happening – matter only accounts for 30 per cent of the density. Exploding stars Type Ia supernovae occur in binary systems when a white dwarf’s gravity pulls material from the other star onto itself, causing it to explode, briefly outshining all other stars in its galaxy. Their intrinsic brightness is known, so their distances can be calculated from how dim they appear. Using this, scientists were able to show that the universe’s…

1 Big Bang In an infinitely dense moment some 13.8 billion years ago, our universe was born from a singularity. 2 Cosmic microwave background After about 380,000 years, subatomic particles known as electrons cooled enough to combine with protons. The universe became transparent to light and the CMB began to shine. 3 Dark ages Clouds of dark hydrogen gas cooled before joining together. 4 First stars Gas clouds collapsed and fusion in stars began. 5 Galaxy formation Gravity caused galaxies to form, merge and drift. Dark energy accelerated the expansion of the universe, but at a much slower rate. Rapid inflation According to the theory of inflation, the universe expanded rapidly for a fraction of a second after the Big Bang. The easiest way to visualise the inflation of the…

One of the most remarkable aspects of the universe is that it’s given rise – at least once – to intelligent life. Life of any kind is only possible because of a handful of basic parameters of nature, such as those which control the strength of forces within and between atoms and those that permit the existence of a stable universe at all. The precise values of these parameters allow the creation of stable elements, the existence of habitable planets and the formation of complex molecules. Instinctively it may feel like this level of ‘fine-tuning’ is too big a stroke of good fortune to happen by chance, but the so-called anthropic (human-centred) principle points out a possible flaw in this logic: we shouldn’t be too surprised that the universe seems…

200 billion Estimated number of galaxies in the observable universe 9.46 trillion kilometres A light year, the distance light travels in one Earth year 46.5 billion light years The distance of an object at the limit of our observable universe 2.726k The measured temperature of CMB radiation in Kelvin 21.5 km/s per million light years The average rate at which objects move away from each other in the universe due to the expansion of space…

Although the Big Bang is often described as an explosion, that’s a misleading image. In an explosion, fragments are flung out from a central point into a pre-existing space. If you were at the central point, you’d see all the fragments moving away from you with roughly the same speed. But the Big Bang wasn’t like that. It was an expansion of space itself – a concept that comes out of Einstein’s equations of general relativity but has no counterpart in the classical physics of everyday life. It means that all the distances in the universe are stretching out at the same rate. Any two galaxies separated by distance X are receding from each other at the same speed, while a galaxy at distance 2X recedes at twice that speed.…

1 Alonely cloud of gas In order for what astronomers call a small galaxy to be made, a relatively large and isolated gas cloud is needed. 2 The making of stars Under gravity, the cloud will collapse because there’s not enough pressure from the gas itself to fight against it. Baby stars are made in the fight between gravity and pressure. 3 Forming a disc The matter spins quickly, causing a flattened disc-like structure. At the centre is a bulge where the older first-generation stars can be found. The rest of the disc is teeming with younger stars. 4 Agalaxy with arms Internal processes make the arms and bars found in spiral galaxies. However, if conditions are more favourable, a lenticular galaxy – an intermediate between an elliptical and a spiral…

The first observational evidence for a black hole emerged in 1971, coming from a binary star system within our own galaxy. Called Cygnus X-1, the system produces some of the universe’s brightest X-rays. These don’t emanate from the black hole itself, or from its visible companion star, which is enormous at 33 times the mass of our own Sun. Instead matter is constantly being stripped from the giant star and dragged into an accretion disc around the black hole, and it’s from this accretion disc that the X-rays are emitted. As was the case with HR 6819, astronomers used observed star motion to estimate the mass of the unseen object in Cygnus X-1. The latest calculations put the dark object at 21 solar masses, concentrated into such a small space…

Anatomy of a black hole 1 Singularity The core of a black hole is a mysterious point of infinite mass called a singularity, where our currently known laws of physics break down. 2 Event horizon The point of no return; this is where the gravity from the extreme curvature of space-time is so strong that not even light can escape. 3 Ergosphere An oblate zone around a rotating black hole, the ergosphere is a volume of space from where energy and mass can be extracted from the black hole. 4 Static limit The edge of the ergosphere. Everything inside the static limit is caught up by the mass of the black hole dragging the fabric of space-time with it as it rotates. 5 Accretion disc An active black hole siphons and steals matter,…

Our Solar System consists of the area influenced by the Sun and, apart from occasional stray visitors from interstellar space, everything it contains. Aside from the Sun, its main components are the eight major planets, their moons and rings, a handful of worlds classified as dwarf planets and vast numbers of smaller bodies made of varying amounts of rock and ice, which are broadly termed asteroids and comets. Most of these objects orbit in a plane roughly in line with the Sun’s equator and in the same direction as the Sun’s rotation – anticlockwise when viewed from ‘above’ the plane. The four innermost planets are mostly composed of dense rock and metal. Earth is the largest of these ‘terrestrial’ planets, with Venus almost the same size, Mars significantly smaller and…

It’s perhaps of little wonder that with our own planetary biases, much of our search for exoplanets has hinged on the search for worlds similar to Earth in both composition and location in the habitable zone of their main sequence stars. Another condition that would make a world similar to Earth would be a magnetic field, which can prevent an atmosphere from being stripped away and thus sustain life. Several of the planets in the exoplanet catalogue are similar to Earth in a range of ways, be it distance from their star, their mass or their radius. Below are 21 candidates for Earth-analogue worlds. But even if these worlds do fit the description of a ‘planet B’ that could be occupied by humans in the future, crewed travel to worlds outside the…

1 Not a scorcher The sunshield keeps the scientific instruments at a constant temperature of -110 degrees Celsius (-166 degrees Fahrenheit). It has thermal insulation and is resistant to temperatures between -170 and 70 degrees Celsius (-274 and 158 degrees Fahrenheit). 2 Sensitive sensors Gaia has sensors that are so powerful they can detect faint objects with a luminosity 400,000 times lower than the naked eye is capable of seeing. 3 Strong signal The average UK broadband speed is 14.7Mbps. While Gaia’s 8.7Mbps may seem slow in comparison, considering it’s beaming from 1.5 million kilometres (932,000 miles) away, it’s quite good. 4 Packing light? Gaia’s got some payload: ten mirrors, an astrometry function, a photometry function and a spectrometry function all within the one unit on a spacecraft three metres…

Astronomers may have finally discovered a moon orbiting around a planet outside our Solar System. The development could have important implications for our understanding of how planetary systems evolve, as well as indicating how typical the planets of our Solar System are. Since the first discovery of planets around stars other than the Sun was made in the early 1990s, our catalogue of planets outside the Solar System has burgeoned, now containing over 4,000 confirmed worlds. One of the most important aspects of our investigation of these extrasolar planets – or exoplanets – is the assessment of how similar or diverse they are in comparison to the planets of the Solar System. It’s unsurprising given how Earth’s own Moon has dominated our imagination and played a vital role in both…

Transit timing method The transit timing method works by measuring a change in the regular transit of a planet. As a planet swings around a star, if there are other objects in its vicinity then it can affect how often a transit is completed. This often indicates the presence of other planets in the system, but in theory the method could be used to hunt for large exomoons as well, revealing their tug on their parent planets. It’s hard to distinguish between an exoplanet and an exomoon via this method, though, so it might be difficult to make a discovery with it. Radial velocity method When an exoplanet orbits a star, its gravity can cause a tug on the star, making its presence noticeable to us on Earth. The star’s…

The terrestrial planets – Mercury, Venus, Earth and Mars – are separated into similar layers: a hot dense core, a warm pliable mantle and a cooled rocky crust. Mercury is around 70 per cent metallic and 30 per cent rocky. Its core is thought to comprise as much as 85 per cent of the planet, a liquid heart of iron 4,000 kilometres (2,485 miles) in diameter. This is covered by 600 kilometres (373 miles) of silicon-rich mantle and between 100 and 200 kilometres (62 and 124 miles) of rocky crust. Venus was expected to have a similar structure to Earth, but Venus has little magnetic field. Earth’s field is created by rotation and convection in our molten core; Venus does seem to have a molten core, but for some reason…

These stars are classified according to two main parameters: intrinsic luminosity and colour. In these terms, a supergiant is simply any star that lies at the upper end of the luminosity range. But there’s actually quite a difference between blue and red supergiants. A blue supergiant is a comparatively young star that’s so incredibly massive that it burns through all its hydrogen – and hence exits the main sequence – after just a few million years. On the other hand, a red supergiant is a star of somewhat lower mass, though still more than ten times that of our Sun, that’s nearing the end of its life. After passing through the red giant phase of its evolution, it begins a final phase of carbon-forming nuclear fusion, causing it to expand…

1 Massive star For stars in this class, the final stages of main sequence evolution produce an iron-rich inner core. 2 Core collapse When all the nuclear fuel has been used up, the dense core collapses under its own gravity. 3 Neutron formation As gravity compresses the atoms in the core, electrons and protons are squashed together to form neutrons. 4 Outer layer collapse The star’s outer layers also start to collapse, falling into the core at a quarter of the speed of light. 5 Supernova explosion The energy generated by the collapsing core blows off the outer layers in a spectacular supernova explosion. 6 Neutron star All that remains is the incredibly dense core, composed almost entirely of neutrons.…

It’s the majority of matter Invisible dark matter makes up 80 per cent of the mass in the entire universe. It affects light Because of general relativity, dark matter acts as a gravitational lens and ‘bends’ light. It could be a new particle Dark matter could be an undiscovered particle that hardly interacts with normal baryonic matter or radiation. It could be a WIMP Weakly Interacting Massive Particles, formed after the Big Bang, could be one explanation. It could be an axion Evidence for WIMPs is weakening, giving ground to axions as a possible alternative. Newton’s laws may need modifying One alternative to dark matter is tweaking Newton’s laws so that they behave differently at galactic edges. It forms the universe’s structure Scientists think galactic clusters form in an existing…

Earth’s water may have been here since the planet formed, and not delivered later by collisions with icy comets. New research analysed Moon rocks brought to Earth by the Apollo program and sheds light on our planet’s earliest days. Although more than 70 per cent of Earth’s surface is covered in water, overall our planet is relatively poor in water and other volatile molecules compared with most other bodies in the Solar System, said Lars Borg, a planetary scientist at Lawrence Livermore National Laboratory in California. Scientists have long debated how Earth came to possess water. Two major scenarios prevail, and both involve ancient cosmic impacts, the most notorious of which saw the proto-Earth collide with a Mars-size rock dubbed Theia that helped give birth to the Moon. In the…

Supernovae are reasonably common - about two explode every century in a galaxy like our Milky Way. With hundreds of billions of galaxies to observe, astronomers see them on a regular basis. Usually, they’re far away, meaning astronomers can struggle to see them in detail. Astronomers were handed an astronomical gift in 1987 when a Type II supernova exploded in the Large Magellanic Cloud, one of the satellite galaxies of the Milky Way. At just 168,000 light years away, they could observe never-before-seen features of the explosion. It was the first time that astronomers were able to confirm that radioactive decay is responsible for the visible light we see from core-collapse supernovae, for example. SN 1987A was also pivotal in our understanding of the role that neutrinos play. Several hours before…

Betelgeuse Stellar evolution models suggest it should go supernova anytime in the next 100,000 years, when it will be as bright as the full Moon in the night sky. Even before its recent dimming, Betelgeuse showed the most variation of any progenitors. Antares The red eye of the scorpion in the constellation of Scorpius is due to go supernova in the next million years. With a mass 15 to 18 times that of our Sun, it will be spectacular, though its lack of variability suggests it’s not quite ready yet. Mu Cephei Known as ‘Herschel’s Garnet Star’, it’s further away than Betelgeuse, but double its diameter, and therefore perhaps closer to death. Its supernova would likely produce a black hole while providing a ‘guest star’ as bright as Venus. Eta…

Humans have long scanned the heavens for signs of other advanced civilisations in the universe. And we’ve found nothing. Absolutely nothing. So maybe we shouldn’t be so focused on intelligent life, but on any sort of life whatsoever. Sure, a tiny microbe may not be as exciting as swapping stories with distant aliens, but signs of nonintelligent life may be much more common – and much easier to find – in our galaxy. Life, including intelligent life, evolved here on Earth. Yet there shouldn’t be anything particularly remarkable about our planet; it’s just another random world in the galaxy. So if intelligent life happened here, it must be pretty common – widespread enough that we should be seeing signs of alien civilisations all over the place. So, where is everybody?…