This film takes you on a journey… …a journey through time and space. I want to tell you the story of an instrument that has vastly improved our view of the skies, sharpening our perception of the Universe, and penetrating ever deeper toward the furthest edges of space and time. Looking at the night sky we see the familiar twinkle of starlight. Light that has travelled enormous distances to reach us. But we are not seeing the stars themselves flicker… The universe is gloriously transparent. The light from distant stars and galaxies can travel unchanged across space for thousands, millions, even billions of years. But then, in the last few microseconds before that light reaches our eyes, the accurate view of those stars and galaxies is snatched away. This is because, as light passes through our atmosphere, the ever changing blankets of air, water vapour and dust, blur the fine cosmic details. So, for many years, astronomers around the world longed for an observatory in space. As early as 1923, the famed German rocket scientist Hermann Oberth suggested a space-based telescope. However, it was decades before technology caught up with the dream. The American astronomer Lyman Spitzer proposed a more realistic plan for a space telescope in 1946. From a position in space, above Earth's atmosphere, a telescope would be able to detect the pristine light from stars, galaxies, and other objects, well before it was distorted by the air we breathe. The result: much sharper images than even the largest telescopes on the ground can achieve; images limited in sharpness only by the quality of the optics. In the 1970s, NASA - the National Aeronautics and Space Administration - and ESA - the European Space Agency - began working together to design and build what would become the Hubble Space Telescope. The name is a tribute to Edwin Powell Hubble - the founder of modern cosmology - who, in the 1920s, proved that not all that we see in the sky lies within the Milky Way. Instead, the cosmos extends far, far beyond. Hubble's work changed our perception of mankind's place in the Universe forever and the choice of naming the most magnificent telescope of all time after Edwin Hubble could not have been more appropriate. It took two decades of dedicated collaboration between scientists, engineers and contractors from many countries before Hubble was finally finished. On April 24, 1990, five astronauts aboard the space shuttle Discovery left on a journey that changed our vision of the universe for ever! They deployed the eagerly anticipated Space Telescope in an orbit roughly 600 km above the Earth’s surface. On Earth, the astronomers waited impatiently for the first results. But less than two months later it was clear that Hubble’s vision was anything but sharp. The mirror had a serious flaw… A defect in the shape of the mirror prevented Hubble from taking sharp images. The mirror’s edge was too flat, by only a mere fiftieth of the width of a human hair. But to accomplish its mission, Hubble had to be perfect in every tiny detail… The disappointment was almost too great to bear. Not only amongst astronomers, but also for American and European taxpayers… Nevertheless, over the following two years, scientists and engineers from NASA and ESA worked together to design and build a corrective optics package, named COSTAR, for Corrective Optics Space Telescope Axial Replacement. Hubble’s masters now faced another tough decision: which science instrument should they remove so that COSTAR could be fitted to Hubble? They eventually chose the High Speed Photometer. Hubble’s First Servicing Mission in 1993 has gone down in history as one of the highlights of human spaceflight. It captured the attention of both astronomers and the public at large to a degree that no Space Shuttle mission since has achieved. Meticulously planned and brilliantly executed, the mission succeeded on all counts. COSTAR corrected Hubble’s eyesight more perfectly than anyone had dared to hope. When the first images after the servicing came up on the computer screens it was instantly clear that the glasses taken up by the astronauts were completely correcting Hubble's nearsightedness. Hubble was finally in business! That was only the first time the Space Shuttle visited Hubble. The telescope was designed to be upgraded, to keep utilizing new capabilities. When more advanced instruments, electrical or mechanical components become available, they could be installed. Plus, just as your car needs servicing, so Hubble needs tuning-up from time to time. Engineers and scientists periodically send the Shuttle to Hubble, so that astronauts can upgrade it, using wrenches, screwdrivers and power tools, just as your mechanic does with a car. There have been four Servicing missions so far – in 1993, 1997, 1999 and 2002 – all undertaken by astronauts, transported into space by NASA’s Space Shuttle. The next one was supposed to occur in 2005, but was unfortunately cancelled in the aftermath of the tragic Columbia crash. Hubble’s future is uncertain. It was originally designed to operate for 15 years, but it is now expected thats its life could be extended to 20 years. Hubble is still producing the most astonishing results that astronomers have ever known. Hubble's important mission will eventually come to an end. An unmanned probe will link up with Hubble in orbit and dock with it. When leaving Hubble, the robot will leave behind a rocket-module so that, after some more years of fruitful observing, engineers on the ground can activate these rockets to control Hubble’s final descent into the atmosphere and to a peaceful final resting place, in the ocean. However, the retirement of the Hubble Space Telescope will not signal the end of our unrivalled view of the universe. Rather, it will mark a new beginning, an era of even more amazing discoveries and images from space. For Hubble has a successor. The James Webb Space Telescope is being designed right now and may be launched as early as 2011. When that day comes, scientists using the James Webb Space Telescope hope to discover and understand even more about our fascinating universe. Hubble is an upgradeable, space-based telescope orbiting at almost 600 km, placing it well above most of our image-distorting atmosphere. It takes about 97 minutes to complete each orbit. It is designed to take high-resolution images and accurate spectra by concentrating starlight to form sharper images than are possible from the ground, where the atmospheric ‘twinkling' of the stars limits the clarity. To gather as much light as possible from the faint objects it studies, any telescope needs the largest mirror it can get. Despite Hubble’s relatively modest mirror diameter of 2.4 metres, it is more than able to compete with ground-based telescopes that have mirrors 10 or 20 times larger in collecting area. Hubble is a large satellite, about 16 metres long or the size of a small bus. It is also one of the most complicated pieces of technology ever built. It contains more than 3000 sensors that continuously read out the status of the hardware so that technicians on the ground can keep an eye on everything. Time on the Hubble is a precious commodity. Astronomers across the world regularly ask for much more time than is available. Keeping Hubble working 24/7 is no small task. Not a single second must be lost and all tasks either observations or so-called ‘housekeeping’ tasks, such as repositioning of the telescope, or uploading new observing schedules are meticulously planned. For astronomers, the most important components of Hubble are its scientific instruments. There are two groups of instruments in Hubble, here and here. The different instruments serve different purposes – some are for making images, some are designed to dissect the light from the stars and galaxies by spreading it out to form a rainbow-like spectrum. Hubble’s unique vantage point in space makes it capable of observing the infrared and ultraviolet light that is otherwise filtered away by the atmosphere before it can reach telescopes on the ground. These forms of light reveal properties of celestial objects that are otherwise hidden from us. Some instruments, like ACS – the Advanced Camera for Surveys – are better for visible and ultraviolet observations, some, like NICMOS – the Near Infrared Camera and Multi-object Spectrograph – are best for infrared observations. Different mechanical and electrical components keep Hubble functioning. The power for Hubble comes from solar panels on the side, which convert sunlight into electricity. Gyroscopes, star trackers and reaction wheels keep Hubble steady and pointing in the right direction – not too close to the Sun, Moon or Earth as they would destroy the light-sensitive instruments – and accurately towards the objects being studied for hours or days at a time. Hubble has several communication antennae on its side that are necessary for sending observations and other data down to Earth. Hubble sends its data first to a satellite in the Tracking and Data Relay Satellite System, which then downlinks the signal to White Sands, New Mexico. The observations are sent from NASA in the United States to Europe where they are stored in a huge data archive in Munich. No single nation could undertake such an enormous project. Hubble has been a major collaboration between NASA and ESA, the European Space Agency from an early stage in its life. Hubble has been of paramount importance to European astronomy. European astronomers regularly win more than 15% of the observing time with Hubble, resulting in several thousand scientific publications over the years. Two groups of European specialists work with Hubble. There are 15 people from ESA currently working at the Space Telescope Science Institute in the USA, and 20 others make up the Space Telescope-European Coordinating Facility in Munich, Germany. There are no boundaries in space. In this vast Universe, our closest relatives are the objects within the Solar System. We share the same origin and the same destiny… Our Solar System was formed about four and a half billion years ago from a huge gas cloud. Ironically, it could have been the deadly force of a thermonuclear blast from an exploding star in the vicinity that triggered our creation… The devastating force of the blast may have disturbed the precarious equilibrium of the original gas cloud, causing some of the matter to collapse inwards, towards the centre, creating a new star, our Sun, and a minute percentage of the collapsing matter became the multifaceted assembly of planets that we have around us today. We are, in other words, just the leftovers of our Sun’s birth. The planets were born in the rotating disk of dust and gas left behind as our mother star was formed. The rocky planets formed in the inner Solar System while the enigmatic gas giants were formed further out. And then, when a fierce wind of smashed atoms began to blow from the Sun –, or perhaps from hot nearby stars or a nearby supernova only sizable planets could maintain their gaseous surroundings and the last wisps of the tenuous cloud between the planets was whipped away. So in our Solar System’s zoo of celestial bodies there are rocky worlds… … and giant gaseous planets. Even now, there is no exact estimate of how much matter or even how many planets exist within our Solar System… Since Pluto’s discovery in the 1930s, and its satellite Charon’s in the 1970s, astronomers have tried to figure out if there’s anything else out there, beyond the ninth planet. In 2003, Hubble spotted something moving fast enough across the background of faraway stars to be an object within the Solar System. Estimates show that it could be about the size of a planet and it has been named Sedna, after an Inuit goddess. Sedna may be 1500 km in diameter, that’s about three quarters the size of Pluto, but so far away that it appears as just a small cluster of pixels even to Hubble. Nevertheless, it is the largest object discovered in the Solar System since Pluto. The Sun is about 15 billion km from Sedna – 100 times further than Earth’s distance from the Sun – and barely gives out as much light and heat as the full moon. So Sedna is engulfed in an eternal bleak winter… Sedna is not the only mysterious object out there. Debris from the formation of the planets is still floating everywhere in the form of asteroids and comets of various shapes and sizes. Sometimes their orbits can lead them on catastrophic courses … The Hubble Space Telescope witnessed the final journey of the comet Shoemaker-Levy 9… It was torn into numerous pieces by Jupiter's gravitational pull when it passed the massive planet in the summer of 1992. Two years later, these fragments returned and drove straight into the heart of Jupiter’s atmosphere. Hubble followed the comet fragments on their last journey and delivered stunning high-resolution images of the impact scars. Our Earth could easily fit into any of these black bruises… Space probes with sophisticated instruments are frequently sent to the planets of our Solar System. They provide close-up investigations of these distant places. Hubble, too, provides its own unique service, by opening a window on our Solar System that is never closed. We’ve gained unprecedented views of storms on other planets, … their changing seasons …and unprecedented views of other atmospheric events, such as aurorae, known on Earth as the northern and southern lights. Even though the solar system clearly has many more surprises in store for us, Hubble has also turned its eye out towards other stars, looking for planetary systems. Astronomers are beginning their search for life elsewhere in the Universe. To start with, they are concentrating on finding earth-like planets. In 2001, Hubble made the first direct detection of the atmosphere of an extra-solar planet and partially determined its composition. Measuring the chemical makeup of extra-solar planetary atmospheres will one day allow us to search for the markers of life beyond Earth. All living things breathe and this changes the composition of the atmosphere in readily detectable ways. Astronomers believe there are many planetary systems similar to ours, orbiting other stars throughout the Galaxy. The birth, life, death and rebirth of stars continues in an unending cycle, in which stars, born of gas and dust, will shine for millions or billions of years, die and return as gas and dust to form new stars. The by-products of this continual process include planets and the chemical elements that make life possible. So through the entire vastness of space the eternal ebb and flow of life continues… Our Sun, that vital source of energy for life on Earth, is a star. A totally unexceptional star, just like billions of others that we can find throughout the Galaxy. A star is nothing but a sphere of glowing gas. It forms out of a compressed cloud of gas and releases energy steadily, throughout its life, because a continual chain of nuclear reactions takes place in its core. Most stars combine hydrogen atoms to form helium through the process called nuclear fusion - the same process that powers a devastating hydrogen bomb. In fact, stars are nuclear factories that convert lighter elements into heavier elements in a series of fusion reactions. They will keep glowing until they run out of ‘fuel’. And that’s it - a star’s life: a quiet beginning and a steady progress to a sometimes violent end. But how can we be certain of this picture when an individual star like our sun outlives humans by a factor of a few hundred million? To investigate the lifecycle of a particular organism on Earth, we don’t have to track an individual specimen’s entire life. Instead, we can observe many of the organisms at once. This will show us all the different phases of its life cycle. For example, each stage of a person’s life is a snapshot of the human experience. And so it is with stars... Stars live and die over millions, or even billions, of years. Even the most reckless stars live for at least one million years – longer than the entire history of mankind! And that’s why it is extremely unusual to be able to track age-related changes in individual stars. To learn more about stars, we must sample different stars at every stage of life and piece together the whole cycle from birth to death. Hubble’s vivid images have documented the tumultuous birth of stars and delivered many, astonishing pictures in colourful detail. The birth of stars in neighbouring stellar ‘maternity wards’ can be used as a time machine to replay the events that created our Solar System. Hubble has often had to work hard for this information because these important clues about our genesis lie hidden behind the veil of gently glowing, dust-laden molecular clouds where stars are formed. Right now there are stars forming everywhere in the Universe. Enormous glowing pillars of dusty hydrogen gas stand sentinel over their cradles, basking in the light of nearby, newly-formed stars. Hubble’s ability to observe infrared light enables it to penetrate the dust and gas and reveal the newly born stars as never before. One of the most exciting of Hubble’s many discoveries was the observation of dust disks surrounding some newborn stars, buried deep inside the Orion Nebula. Here we are actually seeing the creation of new Solar Systems where planets will eventually form. Just as they did in our own Solar system four and a half billion years ago. In the first stages of their lives, stars can stock up on gas from their original birth cloud. Material falling into the star creates bubbles or even jets as it is heated and blasted along a path that follows the star's rotation axis, like an axle through a wheel. Often many stars are born from the same cloud of gas and dust. Some may stay together through their whole lifetime, keeping step as they evolve, like childhood friends that you keep for life. The stars in a cluster will all have the same age, but will have a range of different masses. And this means that very different destinies await them. Human existence is the mere blink of an eye compared with the life of a star. So the direct observation of a transition between different stages of a star’s life can only come about by lucky chance. In fifteen highly productive years, Hubble has allowed us to observe some stars ageing in real time. The telescope has produced startling “movies” that allow us to witness how some of them DO modify their appearance over this minute span of astronomical time. The stars containing the most mass end their lives cataclysmically, destroying themselves in titanic stellar explosions known as supernovae. For a few glorious months, each becomes one of the brightest objects in the entire Universe, outshining all the other stars in its parent galaxy. Since its launch in 1990, Hubble has watched the drama unfold in supernova 1987A, the nearest exploding star in modern times. The telescope has been monitoring a ring of gas surrounding the supernova blast. Hubble has observed the appearance of bright spots along the ring, like gemstones on a necklace. These cosmic pearls are now beeing lit by supersonic shocks unleashed during the explosion of the star. The ruins of an exploding star can hide a powerful engine. Hubble has probed the mysterious heart of the Crab Nebula, the tattered remains of an exploding star, vividly described by Chinese astronomers in 1054, and has revealed its dynamic centre. The innermost region of this nebula harbours a special type of star, a pulsar. Like a beacon, this star rotates, emitting light and energy in a beam. And it powers the vast nebula of dust and gas surrounding it. However, not all stars end their lives so violently. Sun-like stars cool down once they run out of hydrogen. The centre collapses in on itself and the heavier elements are burnt, causing the outer layers to expand and leak slowly into space. At this stage in a star’s life, it is called a “red giant”. Our Sun will become a “red-giant” in a few billion years. At that time, it will expand so much that it will swallow Mercury, Venus and our planet, too. But these stars are not finished quite yet. They can still become something extraordinary… Just before they breathe their last breath, stars like our Sun go out in a final blaze of glory. In its final stages of nuclear fusion, stellar winds blow from the star, causing the red giant to swell to an enormous size. At the heart of this expansion, the exposed heart of the star floods the gaseous envelope with powerful ultraviolet light, making it glow. Because to early telescopic astronomers, these amazing constructions looked a bit like the newly discovered planet Uranus, they became known as planetary nebulae. Hubble's keen perception shows that planetary nebulae are like butterflies: no two are alike. Hubble’s dazzling collection of planetary nebulae show surprisingly intricate, glowing patterns: pinwheels, swirling jets, elegant goblet shapes, barrel shapes, or even rocket engine exhausts. From its unique position high above the distorting atmosphere Hubble is the only telescope that can observe the swollen outer envelope of these dying stars in full detail. Here we flip back and forth between Hubble images from 1994 and 2002. One of the greatest mysteries in modern astrophysics is how a simple, spherical gas ball such as our Sun, can give rise to these intricate structures..!! For some planetary nebulae it is as if a cosmic garden sprinkler created the jets that stream out in opposite directions. …Or could these amazing patterns possibly be sculpted by the magnetic field of a companion star that funnels the emitted gas into a jet? Whatever their cause, in only ten thousand years these fleeting cosmic flowers disperse in space. Just as real flowers fertilize their surroundings as they decompose, the chemical elements produced inside the star during its life are dispersed by the planetary nebula to nourish the space around it, providing the raw material for new generations of stars, planets and possibly even life. Because they disappear so quickly on a cosmic timescale there are never more than about 15000 planetary nebulae at any one time in our Milky Way. A more lasting monument to the dead star, is the tiny heart it leaves behind. Known as a white dwarf, each of these exceptionally dense, Earth-sized stars are fated to spend the rest of eternity gradually leaking their residual heat into space, until eventually, in many billions of years, they approach the frigid –270 degrees centigrade of space. We live inside a huge star system, or galaxy, known as the Milky Way. Seen from outside, the Milky Way is a gigantic spiral, consisting of a central hub embraced by long arms. The whole system slowly rotates. Between the stars there are vast amounts of gas and dust - that we can see - and some unknown material called “Dark Matter” that is invisible to us. Far from the centre, out in one of the arms, the suburbs of the Milky Way, there’s a tiny star system, our home, the Solar System. When we look upon a clear night, we can see about 5000 of the closest stars. Our eyes struggle to see beyond a thousand light-years because of the dust that blankets space and dims the distant starlight. So without a telescope we can only see a minute portion of the entire 100000-light-year-wide Milky Way. For the Milky Way contains several hundred billion stars, many like our own Sun!! Although several hundred thousand million is an almost unfathomable number, it is only the beginning. Astronomers believe there are more than a hundred billion galaxies in the Universe. How many stars would that be? In a handful of sand there can easily be 50,000 individual grains of sand. Even so, on an entire beach there are only just enough grains of sand to represent each star in the Milky Way. There are so many stars in the Universe that we would need to count every grain of sand on every beach on the entire Earth to get anywhere near the right number! Let’s take a grain of sand, 1 mm across, and place it here to represent the size of the Sun. If we started walking towards the nearest star it would take us the better part of a day to complete the journey because the star would be nearly 30 kilometres away. So, galaxies are mostly large collections of emptiness. If we could squeeze together all the stars in the Milky Way, they would easily fit into the volume of space between our Sun and the nearest star. In fact, to completely fill that volume, we would have to pack in all the stars from all the galaxies in the entire Universe!! When looking at the night sky, the universe seems motionless. This is because our life spans are nothing but brief drops in the universal ocean of time. In fact, the universe is in constant motion, but we would need to watch for vastly longer than a lifetime to perceive that motion in the night sky. Given enough time, we would see stars and galaxies move. Stars orbit the centre of the Milky Way and galaxies are pulled together by each other’s gravity. Sometimes they even collide. Hubble has observed numerous galaxies crashing together. Like majestic ships in the grandest night, galaxies can slip ever closer until their mutual gravitational interaction begins to mould them into intricate figures that are finally, and irreversibly, woven together. It is an immense cosmic dance, choreographed by gravity. When two galaxies collide, it’s not like a car crash or two billiard balls hitting each other, it is more like interlocking your fingers. Most of the stars in the galaxies will pass unharmed through the collision. At worst, gravity will fling them out, along with dust and gas to create long streamers that stretch a hundred thousand light-years or more. The two galaxies, trapped in their deadly gravitational embrace, will continue to orbit each other, ripping out more gas and stars to add to the tails. Eventually, hundreds of millions of years from now, the two galaxies will settle into a single, combined galaxy. It is believed that many present-day galaxies, including the Milky Way, were assembled from such a coalescence of smaller galaxies, occurring over billions of years. Triggered by the colossal and violent interaction between the galaxies, stars form from large clouds of gas in firework bursts, creating brilliant blue star clusters. Our own Milky Way is on a collision course with the nearest large galaxy, the Andromeda galaxy. They are approaching each other at almost 500000 kilometres per hour and, in three billion years, will collide head-on. The direct collision will lead to a magnificent merger between the two galaxies, during which the Milky Way will no longer be the spiral galaxy we are familiar with. Instead, it will evolve into a huge elliptical galaxy, containing all of its own stars and all those of the Andromeda galaxy too. Seen from the Earth the collision will look something like this. Although this will not happen for a very long time, there are other dark forces of nature in play everywhere around us, even as we speak… Black holes are the enigmatic villains of the Universe: swallowing all that comes their way, allowing nothing to escape. So for astronomers, the centre of a black hole is the ultimate unknown... No information can escape from within a black hole’s gravitational stronghold. There is no way to find out what is in there. Not even light can escape. So how do we know that they are even there? Black holes themselves cannot be observed directly. However, astronomers can study the indirect effects of Black Holes because the one thing they have in abundance is gravity. Hubble’s high resolution has revealed the dramatic distorting effects of black holes on their surroundings. And not just gravity, astronomers have found that when material is packed tightly enough around a black hole it can ring like a bell. This is the actual note produced by a black hole 250 million light years from Earth. It reverberates through the disc of matter surrounding the black hole and has been altered to bring it within the range of human hearing. In reality it is a B flat, 57 octaves below middle C. Astronomers believe that black holes are singularities – simple points in space. No volume, no extension, but infinitely dense! Black holes can be created during the final collapse of a massive star, many times the size of the Sun. The stellar corpse left over from the demise and collapse of a massive star can be so heavy that no force in nature can keep it from crumpling under its own weight into an infinitely small volume. Although the matter has apparently disappeared, having been compacted into nothingness, it still exerts a powerful gravitational pull and stars and other objects that come too close can be pulled in. For any black hole there is a point of no-return, called the “event horizon”. Once something – a nearby star say - is pulled in past this point it will never been seen again. On its way towards the event horizon, the doomed star will begin to follow a fatal, spiralling orbit. As the star approaches the black hole still further, the matter closest to the hole feels a greater attraction than the rest of the star, sucking and stretching the star out towards the hole until… … the immense tidal forces pull it to pieces and devour it. There are quirkier aspects to these objects too, a twisting of space and time that warps and slows even the passage of time. All objects with a mass deform the very fabric of space and time, but black holes do this to an extreme degree. According to Einstein’s famous theory of general relativity, an intrepid traveller who could visit a black hole and hang above the event horizon without being swallowed would eventually return to find himself younger than the people he had left behind. Perhaps the most curious objects astronomers have hypothesized about are wormholes. A wormhole is essentially a "shortcut" through space time from one point in the universe to another point in the universe. Maybe wormholes, if they exist, will some day allow travel between regions in space faster than it would take light to make the journey through normal space. Hubble has shown that black holes are most likely to be present at the centre of all galaxies. There is one at the centre of our Milky Way - a giant, super-massive Black Hole, perhaps a million times bigger than those created from the collapse of massive stars. It could be the result of the merger of many star-sized black holes that were formed during the remote history of the galaxy. When two galaxies collide, the black holes at each of their centres will perform an elaborate dance. Long after the two galaxies have merged into one, their central black holes continue to orbit each other for hundreds of millions of years before their final violent merger into a single, weighty black hole. This final process is so powerful that it changes the fabric of spacetime enough that we may be able to observe it from the Earth with a new breed of gravitational-wave telescopes or from special spacecraft in orbit. However, compared with the millions of years it takes for galaxies to merge, the final cataclysm at the cores would be relatively brief. So the odds of seeing such an event are small. Until as recently as 50 years ago, astronomers thought the universe was a mostly peaceful place. But this is far from the truth… Space is often shaken by violent events: cataclysmic explosions of supernovae, collisions of whole galaxies and the tremendous outpouring of energy due to the large amount of matter crashing into Black Holes… The discovery of quasars gave us the first clear glimpse of this turmoil … To ground-based telescopes, quasars look like normal stars. And that is exactly what astronomers first thought they were, naming them “Quasi stellar” objects. But Quasars are in fact much brighter and further away than stars… They can shine more brightly than 1000 normal galaxies and are powered by supermassive Black Holes. Stars that orbit too close are pulled apart, draining into the quasar like water into an enormous cosmic sink. The spiralling gas forms a thick disk, heated to a high temperature by its free-fall motion towards the black hole. The gas blasts its energy into space above and below the disk in colossal jets. Quasars are found in a wide range of galaxies, many of which are violently colliding. There may be a variety of mechanisms for igniting quasars. Collisions between pairs of galaxies could trigger the birth of quasars, but Hubble has shown that even apparently normal, undisturbed galaxies harbour quasars. , But quasars are not the only high energy objects astronomers have found…. A serendipitous discovery is something you find while you’re looking for something else. Such discoveries have often changed the course of astronomy. Gamma Ray Bursts were discovered serendipitously in the late 1960s by U.S. military satellites that were on the lookout for Soviet nuclear tests. Instead of finding the most devastating detonations produced by humans, some of the most powerful blasts in the Universe itself were spotted… These astoundingly energetic blasts of gamma rays are detected at least once per day from random directions in the sky. Although Gamma Ray Bursts last only a few seconds, the energy they release is equal to the amount of energy radiated by our whole Milky Way over a couple of centuries. Gamma rays are not visible to the human eye, and special instrumentation is needed to detect them. For 30 years, no one knew what caused these bursts. It was like seeing the gamma-ray bullet fly by Earth without ever glimpsing the weapon that fired it. Together with nearly all other telescopes in the world Hubble looked for the “smoking gun” for many years. It observed the positions in the sky where gamma ray explosions had been seen, trying to find any object at that location. But all efforts were in vain, until… In 1999 Hubble observations were fundamental in determining that these monstrous outbursts take place in far distant galaxies. The cause could be the blast produced in the final cataclysmic collapse of a massive star… … or the dramatic encounter of two very dense objects, such as two Black Holes, or a Black Hole and a neutron star. Black holes are certainly some of the most exotic objects in the Universe. As well as affecting matter they can also show up in some other spectacular ways because their enormous gravitational fields can also deflect light. In fact, rays of light that pass close to a Black Hole will not follow straight lines, but will be bent onto new paths, creating a natural telescope that can peer further into space than ever thought possible. Just as a wanderer in the desert sees a mirage when light from remote objects is bent by the warm air hovering just above the sand, we may also see mirages in the Universe. The mirages we see with a modern telescope such as the Hubble Space Telescope do not arise from warm air, but instead from remote clusters of galaxies - huge concentrations of matter. Long ago some people thought the Earth was flat. This is in some way understandable - in our daily life we can’t see the curvature of our planet. Space itself is actually curved, even though we can’t see this for ourselves on a starry night. But the curvature of space does create phenomena that we can observe… One of Albert Einstein's predictions is that gravity warps space and therefore distorts rays of light, in the same way that ripples on a pond create a warped honeycomb pattern of light on the sandy bottom. Light from distant galaxies is distorted and magnified by the gravitational field of massive galaxy clusters on its path to Earth. The effect is like looking through a giant magnifying glass and the result is called gravitational lensing. The weird patterns that rays of light create when they encounter a weighty object depend on the nature of the “lensing body”. Thus, the background object can appear in several guises... …Einstein rings where the whole image is boosted and squeezed in a circle of light… …multiple images, ghostly clones of the original distant galaxies… …or distorted into banana-like arcs and arclets. Though Einstein realized in 1915 that this effect would happen in space, he thought it could never be observed from Earth. However in 1919 his calculations were indeed proved to be correct. During a solar eclipse expedition to Principe Island near the west coast of Africa, led by the renowned British astronomer Arthur Eddington, the positions of stars around the obscured solar disk were observed. It was found that the stars had moved a small but measurable distance outwards on the sky, compared with when the Sun was not in the vicinity. Nowadays, faint gravitational images of objects in the distant Universe are observed with the best telescopes on Earth, and, of course, with the sharp-sighted Hubble. Hubble was the first telescope to resolve details within the multiple arcs, revealing the form and internal structure of the lensed background objects directly. In 2003, astronomers deduced that a mysterious arc of light on one of Hubble’s images was the biggest, brightest and hottest star-forming region ever seen in space. It takes fairly massive objects, for example, clusters of galaxies, to make space curve so much that the effect is observable in deep images of the distant Universe - even with Hubble’s astonishing resolution. And so far gravitational lenses have mainly been observed around clusters of galaxies, which are collections of hundreds or thousands of galaxies and are thought to be the largest gravitationally bound structures in the Universe. Astronomers know that the matter we see in the Universe is just a tiny percentage of the total mass that must be there. For matter exerts a gravitational force, and the visible stuff is simply not enough to hold galaxies and clusters of galaxies together. Since the amount of warping of the ‘banana’-shaped images depends on the total mass of the lens, gravitational lensing can be used to ‘weigh’ clusters and to understand the distribution of the hidden dark matter. On clear images from Hubble one can usually associate the different arcs coming from the same background galaxy by eye. This process allows astronomers to study the details of galaxies in the young Universe and too far away to be seen with the present technology and telescopes. A gravitational lens can even act as a kind of ‘natural telescope’. In 2004, Hubble was able to detect the most distant galaxy in the known Universe, using the magnification from just such a ‘gravitational lens’ in space. Light may travel through a vacuum at the highest speed anything can ever reach, but it is still a finite speed. This means that it takes a while for rays of light to travel between two points in space. The speed of light through space is about 300000 kilometres per second. 300 thousand kilometres is nearly the distance from the Earth to the Moon. So it takes light just over a second to travel from the Moon to the Earth. When we look at the Moon we see it as it was just over a second ago. Who hasn’t thought about what it would be like to travel in time? The finite speed of light enables us to get close by allowing us to look back in time. When looking out into space, we just need to wait for the light from distant places to reach us, and it shows how things were when the light began its journey. Powerful instruments, like Hubble, have made it possible to look farther out and farther back than ever before. What cosmologists are seeing is simply astounding. In the 1920s, astronomer Edwin Hubble discovered that most galaxies appear to be moving away from us at a rate proportional to their distance. The farther away a galaxy is, the faster it appears to be moving away from us. This is due to the expansion of the Universe. That expansion began in a titanic explosion, called the Big Bang, many billions of years ago. The rate of expansion holds the key to estimating the age and size of the universe. This rate is called the Hubble constant. The age and size of the universe can be estimated by "running the expansion backwards" – until everything is compressed into that infinitely small point of energy from which the universe was generated. The top ranked scientific justification for building Hubble was to determine the size and age of the Universe. The quest to determine the Hubble constant precisely was headed by the Key Project team, a group of astronomers who used Hubble to look for remote, accurate "milepost markers", a special class of stars called Cepheid variables. Cepheids have very stable and predictable brightness variations. The period of these variations depends strictly on the physical properties of the star, which can be used to determine their distance very effectively. For this reason these stars are better known as ‘standard candles’. The Cepheids have been used as reliable stepping-stones to make distance measurements for supernovae, which are much brighter than Cepheids and so can be seen at far greater distances. Hubble has measured the light from supernova explosions more accurately than any other instrument, mostly due to its high resolution. From the ground an image of a supernova usually blends in with the image of its host galaxy. Hubble can clearly distinguish the light from the two sources. Cepheids and supernovae have given a measure for the scale of the Universe. Today we know the age of the Universe to a much higher precision than ever before: around 14 billion years. For many years astronomers have discussed whether the expansion of the Universe would stop in some distant future, making the universe collapse in a fiery "Big Crunch", or whether it would continue to expand ever more slowly. Combined observations of distant supernovae with Hubble and most of the world’s top-class telescopes were used to measure distances to remote supernovae. And it looks like the expansion of our universe is nowhere near slowing down. Instead, it seems to be speeding up. When Hubble was used to measure how the expansion of the Universe has changed with time, it turned out, quite surprisingly, that during the first half of cosmic history, the expansion rate was actually slowing down. Then, a mysterious force, a sort of "anti-gravity” made the Universe ‘hit the gas pedal’ starting the acceleration we see today. This suggests an extraordinary fate for the Universe because it implies that the anti-gravity force is getting stronger all the time. If this continues, it will eventually overwhelm all gravity and catapult the Universe into a super fast acceleration that will shred everything into its constituent atoms. Cosmologists have called this nightmare scenario, the Big Rip. We are collecting unexpected news from deep space. Just as geologists dig deeper underground to find ever more ancient fossils, bearing witness to ever more remote epochs, so astronomers ‘excavate’ deeper and deeper towards the beginning of time, by looking for light coming from fainter, and thus more distant, objects. Hubble started a new era we could call ‘astroarcheology’ and it began during Christmas, 1995… Pointing the world’s most sophisticated telescope at the same piece of sky for ten days in a row may sound a bit strange. And this was what many astronomers thought when they tried it for the first time at the end of 1995. Deep field observations are long-lasting exposures pointing at a particular region of the sky. They aim to reveal faint objects by collecting as much light as possible over a long period of time. The ‘deeper’ an observation goes, the fainter are the objects that become visible. Objects in the sky can either look faint because their natural brightness is low, or because their distance is great. “When this experiment was first proposed, nobody really knew if this would lead to any interesting scientific results. But when we first looked at the image we were astonished! We could see more than 3000 galaxies in this small field.” The observed region of sky in Ursa Major, the Big Dipper, was carefully selected to be as empty as possible so that Hubble would look far beyond the stars of our own Milky Way and out past nearby galaxies. The thousands of galaxies observed in the first Deep Field were at various stages of evolution and were strung out along a corridor of billions of light-years. This allowed astronomers to study the evolution of these objects through time, glimpsing different galaxies at different stages of their lives. After the first deep field, another long exposure was taken in the Southern sky. Together, the Hubble Deep Field North and South gave astronomers peepholes to the ancient Universe for the first time. Some of the objects viewed on the images were so dim that seeing them would be as difficult as discerning a flashlight on the Moon from Earth. “We could definitely tell that the Hubble Deep Field opened a whole new era of observational cosmology. It formed our view of the distant universe”. The Hubble Deep Fields have caused a real revolution in modern astronomy. After the first Deep Field, almost all ground- and space-based telescopes were pointed to this same area for long periods. Some of the most interesting results in astronomy emerged from this fruitful synergy between instruments of different sizes, in different environments and with sensitivity to different wavelengths. They gave us the first clear picture of the rate of star formation throughout the Universe. Astonishingly, it showed that star formation peaked within a few billion years of the Universe’s creation. At that time, stars were forming at over 10 times the rate they are today. Once they had begun to discover the most distant universe ever seen, Hubble astronomers tried to push their observations even farther back in time. In 2003 and 2004, Hubble performed its deepest exposure ever: the Hubble Ultra Deep Field. It is a 28 day-long exposure, going much deeper than the earlier Hubble Deep Fields North and South. The Hubble Ultra Deep Field reveals the first galaxies to emerge from the so-called "dark ages" - the time shortly after the big bang when the first stars reheated the cold, dark universe. Just after the Big Bang, in the newborn fast-expanding Universe – before the era of the stars and galaxies - the distribution of matter was fairly smooth. As time went on, the king of all forces – gravity – started acting. Slowly, but steadily… Under the influence of gravity from the mysterious dark matter, small clumps of normal matter started to coalesce in regions where the density was slightly higher than average. With no stars to light up space, the universe was in its dark age. Where the density of the clumps became higher, even more matter was attracted, and a competition between the expansion of space and gravity took place. Where gravity won, regions stopped expanding, and started to collapse in on themselves. , The first stars and galaxies were born. Where the matter density was highest – at the intersections between the large web-like structures of matter - the largest structures we know were formed: clusters of galaxies. The Deep Field images are studded with a wide range of galaxies of various sizes, shapes, and colours. Astronomers will spend years studying the myriad shapes of the galaxies in this image to understand how they formed and have evolved since the Big Bang. In vibrant contrast to the image's rich harvest of classic spiral and elliptical galaxies, there is also a zoo of oddball galaxies littering the field. Some look like toothpicks; others like links on a bracelet. A few appear to be interacting with each other. Their strange shapes are a far cry from the majestic spiral and elliptical galaxies we see today. These oddball galaxies chronicle a period when the Universe was more chaotic, when order and structure were just beginning to emerge. One of the great things about Hubble is that there are many instruments onboard that can make different observations at the same time. The Hubble Ultra Deep Field is actually two separate images taken by two instruments: Hubble's ACS camera and the NICMOS instrument. NICMOS sees even farther than the ACS. It detects infrared light, and so it’s able to reveal the farthest galaxies ever seen because the expanding universe has stretched and weakened the light from these objects so much that, they’re now only visible at infrared wavelengths. The Hubble Ultra Deep Field is likely to remain the deepest image of the Universe for the next decade or so, until an ESA Ariane rocket launches the James Webb Space Telescope in 2011. Up until today, during the first 15 years of its life, Hubble has orbited the Earth 80,000 times. This is the same as three and a half billion kilometres or 24 times the distance from the Earth to the Sun. Hubble has taken more than 500000 exposures of the Universe and created a visual heritage that has shaped the way humanity looks at the Universe today. But Hubble’s perhaps greatest legacy has been to open our eyes to the incredible beauty of nature. Not only ‘out there’ in the depths of cosmos, but also everywhere around us in our daily lives. And it’s no where finished yet…
