Hubble Telescope’s Greatest Discoveries [4K]

We live in an age of deep understanding about our universe. From asteroids within the solar system to galaxies at the edge of space, we've seen glimpses of the cosmos our ancestors would have found hard to believe. And a great many of these glimpses owe to one observatory in particular. A telescope which has, for more than 30 years, continuously transformed our understanding of cosmology. The magnificent Hubble Space Telescope. Hubble has provided us with some of our most iconic and breathtaking portraits of the universe, making more than one and a half million observations over three decades of service. And in today's episode, we will use these observations as we relive some of the telescope's grandest achievements, from imaging the most beautiful nearby nebulae, to revealing the secrets of a universe at large. These are some of Hubble's greatest discoveries. The Hubble Telescope is a bus-sized satellite, which launched into space aboard the Space Shuttle Discovery in 1990. Rising high above Earth's atmosphere, it is able to study our universe in crystal-clear resolution, unhampered by atmospheric disturbances and absorption which constrains the potential of ground-based telescopes. Hubble resides in a low-Earth orbit and faces outwards towards space, studying the universe predominantly in the visible and ultraviolet wavelengths, but various upgrades over the years have broadened this capacity to the near-infrared. As mentioned, Hubble has taken more than 1.5 million observations of the cosmos, for more than 12,000 scientific endeavours, its findings being cited in more than 20,000 peer-reviewed papers, some of them yielding the most important information we have about our universe. Hubble has seen generations of stars birthing and dying in spectacular supernovae. It has seen the ghostly emissions of the universe's earliest galaxies, grinding out the first stars at breakneck speed. And it has seen the universe expanding at what appears to be an accelerating rate, with seismic implications on its ultimate fate. As such, the Hubble Telescope has single-handedly defined its own era in astrophysics, an era that now overlaps with that of its successor, the James Webb Telescope. But with such a long, rich history of revolutionary research, it's easy to view Hubble's time in the However, this is far from the reality. In fact, the telescope has had to overcome a number of hurdles during its service, many of which arose in its early years of operation. Remember all those long, painstaking delays to the James Webb Telescope, holding it back year after year? Well, the caution shown by scientists was not without reason. Because even the slightest, tiniest fault in an optical instrument can fundamentally impair its ability to make observations. And this is exactly what happened with the Hubble Telescope in its early years. A month after launching, Hubble switched on and became operational. And initially, test photographs of its first light did show an improvement on the images produced by ground-based observatories. However, within a year, NASA had announced that the initial images being received from the telescope were blurrier than expected, with stars cloaked by fuzzy halos of skewed light, making clear, precise detail difficult to resolve. An internal investigation traced the problem all the way back to the development of the telescope's spherical 2.4-metre primary mirror. Unbeknown to its engineers at the time, the mirror's curvature was marginally off, with a spherical aberration of about two microns. While this deviation equated to only about a fiftieth of the width of a human hair, the mirror was left unbalanced and improperly calibrated for the optical instruments using its light, particularly the Wide Field Planetary Camera, intended to be Hubble's workhorse camera unit. With such fine margins impairing the observatory to such a degree, you can see why scientists were keen to take their time to make sure they got the James Webb Telescope right. The Webb Telescope's position in an orbital zone trailing the Earth makes it effectively impossible to reach the telescope for repairs now it has been deployed. However, the Hubble Telescope's low-Earth orbit did place it within reach of humanity, and thus, NASA scrambled to assemble a servicing mission aimed at salvaging their flailing vision for a pioneering space-based observatory. In the meantime however, despite the shortcomings of the optical instruments, Hubble remained an unrivalled tool for cataloguing and measuring the distances to the brightest extra-galactic stars. Cepheid Variable Stars are volatile stars that pulsate radially on periodic timescales, causing them to vary in size and luminosity on a well-defined basis that can be used as a cosmic benchmark for constraining the distance. This was the same technique used by Mount Wilson astronomer Edwin Hubble, who used Cepheid Variable Stars to prove beyond reasonable doubt that the so-called Andromeda Nebula was actually an independent spiral galaxy lying at least a million light-years beyond the Milky Way. And in mid-1993, Hubble's namesake telescope used this method to precisely measure the distance of another nearby spiral galaxy, Messier 81. Previously, scientists couldn't agree on whether this galaxy was 4 million light-years away or 18 million, as no reliable method could yield precise results. But the Hubble telescope was able to identify Cepheid Variable Stars in M81, accurately measuring its distance to be somewhere in the region of 11 million light-years from Earth. And in doing so, scientists took a major step towards determining the age of the universe. In fact, it was Edwin Hubble himself who demonstrated that a linear relationship exists between a galaxy's distance and the speed at which it appears to be moving away from the Earth. This recession is due to the universe's expansion pushing galaxies apart, and thus, if we know how far a galaxy is from Earth precisely, we can compare that to how fast it appears to be receding, to accurately constrain an estimate for the Hubble constant, which the telescope found to be around 73 kilometres per second per megaparsec. And finally armed with their first precise estimate, scientists were able to extrapolate this expansion backwards, to a point where they could go no further, deriving an estimate for the age of the universe as around 13.5 billion years. This placed a firm market in the sand amid an ongoing debate over whether the universe was 10 or 20 billion years old, and this precise age of 13.8 billion years is a figure that has been rigorously reaffirmed by independent experiments ever since. As 1993 drew to a close, NASA finally embarked on their first servicing mission to Hubble, as astronauts aboard the Space Shuttle Endeavour visited the telescope in orbit, to deliver and install replacement components. While not feasible to replace the flawed primary mirror itself, the shuttle crew were able to swap the internal optical instruments, with updated versions implementing their own corrective optics, the same way glasses would be used to correct the vision of a long-sighted person. In space, the shuttle crew had to gently open Hubble and remove its large internal instruments, with the subtlety and delicacy of handling a sleeping baby. They replaced the unfocused wide-field planetary camera with the updated WIFPIC-2, adjusted and primed to work with Hubble's tricky mirror, able to observe in some 48 colours and filters, in wavelengths ranging from ultraviolet through to the near-infrared. They also installed the COSTAR instrument, which further corrected the telescope's optics, bringing an entirely new level of detail into focus. In January 1994, NASA kicked off another groundbreaking year of Hubble-led advancements by announcing that the spherical aberration in the primary mirror had been rectified, accompanied by a comparison image showcasing the galaxy Messier 100. As you can see, the WIFPIC-2 revealed a landslide of sophisticated, new intrinsic detail within the galaxy. And at last, Hubble was finally set to deliver on its promised glimpse of the clear, unfiltered universe. And with its equally enhanced capacity to take spectroscopic measurements, humanity set its sights on a new target. The heart of the giant elliptical galaxy, Messier 87. M87 is an enormous, ancient titan of a galaxy, lying around 50 million light-years from Earth, at the heart of the Virgo cluster. It is one of the most substantive and studied galaxies outside of our local group, with its glittery, golden halo of starlight enticing the eyes of astronomers since the 18th century. But what really got scientists intrigued in this object was not its starry halo, but rather a long, finger-like stream of matter appearing to stem from the object's bright core. The stream was first described in 1918 by Mount Hamilton astronomer Heber Curtis, who noted the stream of ejecta long before we realised that M87 was a separate galaxy. But the mystery deepened in the mid-20th century, when newly emerging radio surveys found the stream to be radio-loud. M87's jet is one of the most luminous extragalactic radio sources, sparking a debate over what could be occurring within the galaxy's nucleus to drive it. One outlandish explanation was that a supermassive black hole may be lurking at the heart of the galaxy. But back then, black holes were still a wildly theoretical and mathematical notion, with little practical application. But with its broadened, sensitive new array of spectroscopic instruments, Hubble closed the case in 1994, identifying multiple overlapping lines of evidence for the monstrous black hole. At the heart of this elliptical galaxy, Hubble found evidence for a spiral structure in the spectral data, one which propagates at unfathomable speeds. On one side, matter seems to be moving towards the Earth, with its emissions blue-shifted as wave patterns are compressed. Whereas, on the other side, emissions appear red-shifted as the matter moves away from the Earth, elongating the wave patterns. Both sides at the same speed, but in opposite directions. And this is how we determined that the spiral object is actually an accretion disc, of a supermassive black hole the size of the entire solar system, which Hubble estimated to be at least 3 billion times the mass of the sun. Only the immense, unprecedented influence exerted by a gravitationally collapsed object can explain both the speed at which the disc rotates and the resulting jet it produces. As the disc propagates, the gas caught up within is heated to upwards of 10,000 Kelvin, instantly ionising the matter as its electrons are ripped from their atomic nuclei. And as these stray atomic nuclei fall beneath the black hole's event horizon, gravitational potential energy is released, and the surviving charged subatomic particles are funnelled onto the black hole's polar axes, before being blasted out into space at relativistic velocities. This jet is highly magnetised, which accelerates the charged relativistic particles as they zip off into space, glowing with radio-loud synchrotron radiation as they expand for thousands of light years. And thus, Hubble was able to pinpoint a supermassive black hole as the culprit for M87's peculiar jet and radio emissions, also affirming the follow-up notion that most large galaxies contain a similar supermassive black hole lurking within their cores. Rejuvenated, and with its potential finally being realised, Hubble's gaze was directed back towards the solar system, just in time to observe the epic climax of a comet shatter event around Jupiter. Comets are chunks of icy debris which traverse the solar system in highly eccentric, elliptical orbits. Ordinarily, they orbit the sun, but they can become entrapped by the gravity of large planets like Jupiter. And this is exactly what happened to comet Shoemaker-Levy 9. Starting in 1992, Shoemaker-Levy 9 drew too close to the Godfather planet, where it began to disintegrate under Jupiter's immense, vice-like gravitational field. By 1994, the comet had broken into no less than 21 fragments, some of which were more than a kilometre in length. And in July, Hubble witnessed these chunks as they plunged into Jupiter's atmosphere, leaving large, visible impacts which revealed the secrets of the gas giant's chemistry. Over six days, each of the fragments struck the Godfather planet, travelling at speeds of around 60 kilometres per second on impact. They smashed into the Jovian gas, heating pockets to more than 30,000 Kelvin, causing eruptions which rose more than 3,000 kilometres above the cloud These eruptions then settled into a series of striking, dark, bruise-like patches on the surface of Jupiter's atmosphere, which persisted for a number of weeks. And as these bruises gradually began to disperse in Jupiter's winds, their distinctive appearance made them ideal chemical tracers for mapping the paths of the Jovian weather fronts, allowing us to observe its atmosphere in a new light, providing fresh insights into its chemical composition. Shoemaker-Levy 9 was the first time that such an impact like this had been witnessed, let alone in such incredible detail, one of a number of firsts for the Hubble telescope that would continue into 1995. After producing surface maps of Saturn's cloud-covered moon of Titan, and then detecting water vapour in the atmosphere of Jupiter's moon Europa, Hubble turned its attention to the Eagle Nebula, specifically a dense, gaseous interior region of starbirth, nicknamed the Pillars of Creation. These long, trunk-like tubes line the cradles for new generations of stars, as young nuclear fires spring up out of the abundances of star-forming gas. And Hubble's view of this stellar synthesis in action sent ripples cascading throughout the world, seen to this day in all sorts of weird and wonderful modern settings, from t-shirts, to printouts, to phone backgrounds, to wallpapers, as it captured the eyes of the entire world, bringing global attention to the plight of the Hubble telescope. But an even more impactful image was only just around the corner, as Hubble scientists finished up their analysis of one of its most ambitious targets to date, seemingly empty space. In the previous year, the then-director of the Space Telescope Science Institute, Robert Williams, became intrigued by Hubble's newfound ability to gather light from the distant universe, after studying exposures taken with the upgraded WFPG-2 camera. With a range of galaxies visible at varying times in the universe's life, he suspected that another, longer exposure in a sufficiently dark portion of the sky may reveal even more galaxies which could be used to create a cosmic zoo mosaic of space. Back then, Williams was responsible for allocating about a tenth of Hubble's operational time, usually to high-ranking physicists looking to study transient phenomena, such as extra-galactic supernovae. But after assembling a team, Williams spent the next year scouring the sky for a small, dark corner of space, with a view to using his discretionary time slots to capture unseen light from the distant universe. A pin-sized patch of sky in the constellation of Ursa Major was chosen, with no nearby stars or apparent backdrop galaxies, lying sufficiently far from the Milky Way's opaque, extinguishing galactic plane. And over ten consecutive days in December 1995, the Hubble Telescope made 342 observations of the region, collecting light in a range of wavelengths, photon by photon. If nothing was found, it would have been an embarrassing waste of Hubble's already precious operational time. But in early 1996, the observations were assembled and released to the public, and the world saw the Hubble Deep Field. This through-the-keyhole mosaic of deep space is a journey to the edge of the visible universe, capturing a timeline of more than 3,000 galaxies at almost every evolutionary stage, dating back more than 10 billion years. Of all the millions of incredible, jaw-dropping Hubble images, if we had to pick one as being the most significant, and most groundbreaking, it would probably be this one. More than anything else, the Hubble Deep Field showed us what the universe really looks like on its largest scales, with stars and galaxies at a wider range of depths and times than scientists ever expected. And what makes this image even harder to comprehend, is that this tiny section of the sky is just one tile across a night sky expanse containing more than 10 million, each providing their own account of the universe's evolutionary history through the keyhole. In the following year, a follow-up Deep Field image was taken in a disparate section of the sky to ensure the original was a true representation of the cosmic scale, and the results of the Hubble Deep Field South were much the same. During this time, in February 1997, Hubble received its second servicing upgrade, as a seven-member crew aboard the Space Shuttle Discovery installed a set of new optical and spectroscopic instruments, including a new infrared camera. These enhancements broadened Hubble's capacity to take high-resolution images of the distant universe, whose emissions have been shifted most prominently into the infrared bands. And with the greatest range of cosmic distances now unlocked, scientists set about attempting to measure the universe's rate of expansion over time. As we mentioned, Hubble had some years earlier estimated the Hubble constant to be around 73 kilometres per second, per megaparsec. But over the longest timescales, we actually expect this constant to have varied, according to the size and density of the universe. At the time of the Deep Field images, scientists expected to find the Hubble constant decelerating, on the road to stopping altogether, as would be the expected behaviour in a universe dominated by gravity. But instead, in 1998, two teams of scientists using the Hubble telescope to probe the farthest supernovae found evidence for the opposite. In the more recent half of its life, the universe's expansion appears to have accelerated, in fact. And thus we were able to conclude that there must be something more than gravity out there, acting upon the cosmos and accelerating its growth. This revelation transformed cosmology, as Hubble had stumbled upon preliminary evidence for dark energy. A mysterious, anti-gravity-like force, stretching the universe apart like a rubber band, the likes of which now makes up an immutable part of the science we teach in textbooks. As the 90s drew to a close, the sun set on an extraordinary decade of Hubble-led revelations which changed the world. However, just before the turn of the 2000s, Hubble had to be switched to safe mode following a number of critical instrument failures, effectively putting the telescope on standby with its solar panels facing the sun. Only another servicing mission to Hubble could rectify these flaws, one which was already in planning as a general maintenance mission, but suddenly became a rescue mission. Servicing mission 3 was split into two separate launches as a result, one to salvage the telescope and replace its critical instruments, and another at a later date to perform non-essential upgrades. The first leg of this initiative, SM3A, took place over nine days in December 1999. Astronauts serviced Hubble's batteries and fitted it with six new, fresh gyroscopes, as well as a new, more efficient computer unit. These repairs restored Hubble to a functional state, bringing it out of safe mode and resuming its research. And with part two of the servicing mission set for 2002, Hubble reopened its eye to usher in another decade it would come to define. Hubble spent the early years of the new millennium focusing its eye on extra-solar planets, worlds orbiting stars other than our sun. Its first stop was to the Orion Nebula, to capture star systems like the solar system in their infancy. In 2001, Hubble snapped the first direct visual evidence of Proplids, a proto-planetary disc of dust and gas, surrounding a new star that has only just begun to shine. This dust is in the process of crystallising and forming a sort of gravel, which would ordinarily be used to build up rocky planetary cores. However, the Orion Nebula is a star-birthing factory, brimming with blistering, ionising stellar wind. And so, for new stars in the Orion Nebula, their Proplids will probably stop short of forming any significant planetary systems, as dust is irradiated and driven away. But in other, less hostile star systems, like our solar system, this process is what enables the formation of exoplanets, from Earth-like water worlds to massive, godfather gas giants. But in both cases, trying to image such a planet directly is a near-impossible task for any telescope, like trying to image grains of sand on the horizon at night. However, there are a number of ways we can indirectly detect and observe exoplanets, the main one being by waiting for said planet to pass in front of its parent star relative to the Earth, causing a dimming in its emissions. Even if this dimming is only by 1 or 2%, our most sophisticated observatories can measure the flicker, to reverse-engineer the passing planet's properties. But Hubble's freshly-sharpened instruments were able to take this a step further, collecting the starlight passing through a transiting exoplanet's atmosphere to deduce its chemical composition. Osiris is a large, Jupiter-like gas giant, lying 150 light-years from Earth, in the constellation of Pegasus. The planet lies very close to its parent star and thus transits frequently, allowing for regular observations from a number of vantage points. And in late 2001, scientists used this transit data to identify traces of sodium in Osiris' atmosphere. While the discovery itself was of little significance, it demonstrated that particularly sensitive observatories could be used to probe exoplanetary atmospheres, a practice that has since become central to NASA's exoplanet hunting initiatives, like the Kepler spacecraft. And in the years since, we've studied thousands of alien atmospheres, a search that is continued to this day by the James Webb Telescope. In the following year, the second phase of the third servicing mission, SM-3B, was carried out by Space Shuttle astronauts, who installed a host of new instruments and capabilities into Hubble's mainframe. Among them was the Advanced Camera for Surveys, a new tri-camera instrument ten times more efficient than the last of Hubble's original instruments it replaced. They also replaced the telescope's entire power control unit, in a kind of open-heart surgery for Hubble, requiring it to be completely switched off for the first time since its launch in 1990. But much like its predecessors, SM-3B was a roaring success, and though a final servicing mission would be needed to rectify all of the aging telescope's issues, Hubble was once again left more capable and versatile than at any point prior. And to celebrate, NASA snapped a host of beautiful new images utilising its newest instruments, from awesome views of the inside of nebulae, to shots of colliding galaxies millions of light-years from Earth. In 2003, a tragedy befell the world which upended NASA's Space Shuttle programme, when the shuttle Columbia disintegrated upon re-entry to Earth's atmosphere, killing all seven crew members on board. In the wake of the disaster, Hubble's final servicing mission was scrapped, followed soon after by George W. Bush's announcement that the shuttle programme would be wound down to make way for the International Space Station. But even in light of its uncertain future, Hubble continued to bedazzle the world. In March 2004, Hubble scientists lightened the mood by releasing the ultra-deep-field image. Another, even deeper exposure of the universe, creating a new cosmic timeline illustrated by more than 10,000 galaxies. Compiled from more than 800 exposures to a spot lying in the constellation of Fornax, the ultra-deep-field image proved to be an earth-shattering successor to the original deep field, as our most complete, all-encapsulating view of the cosmos to that point. It brought galaxies into focus which existed 13 billion years ago, only 800 million years after the birth of the universe, many of which were among the farthest galaxies discovered at the time. But in the years that followed, Hubble's mechanical breakdown continued, notwithstanding its recent servicing mission. While Hubble was still able to carry out scientific research, it was clear that the telescope would once again need repair work in space to keep it at the forefront of human engineering, and thus NASA mulled over reinstating Servicing Mission 4. In the meantime, Hubble turned its attention back to our solar system, continuing its incredible chain of discoveries, this time a little closer to home. In 2005, Hubble imaged our solar system's ninth planet, as it was considered back then, Pluto. And in doing so, its observations revealed two new, previously undetected moons around the dwarf planet, some 5,000 times fainter than Pluto itself. These satellites, named Hydra and Nix, have similar dimensions of just over 50 kilometres. A pair of city-sized objects, each smaller than LA, spotted from more than 5 billion kilometres distant. In 2006, a report into the completeness of the ISS recommended more than a dozen additional assembly missions before the Space Shuttle could be retired, and thus Hubble's fifth and final servicing mission was reinstated. But it would not take place until 2009, as a stream of new issues plaguing the telescope arose during planning. In 2008, shortly after completing its 100,000th orbit of Earth, Hubble re-entered safe mode following a failure in the observatory's data formatter, responsible for processing observational data for beaming back to the ground. Once again, the telescope closed its eye and basked in the light of the sun, as it halted its observations and waited for help. Servicing mission 4 wouldn't reach the until the following year, but this bumper upgrade to Hubble single-handedly rectified all of its most troubling issues. Over a number of days in May 2009, astronauts replaced Hubble's gyroscopes, batteries and its insulation, while repairing and installing new optical instruments. The WIFPIC-2, Hubble's resoundingly successful workhorse camera for 16 years, was finally retrieved and replaced by the WIFPIC-3, made from parts recycled from the original unfocused wide-field planetary camera. They also installed the Cosmic Origins Spectrograph, and restored the Dormant Infrared Camera and Space Telescope Imaging Spectrograph, the first and only repair of the telescope's instruments to have occurred in orbit. Recharged, kitted out and ready for its longest ride, astronauts aboard the Space Shuttle Atlantis bid farewell to the Hubble Telescope for the final time. And with almost every ageing component completely rejuvenated, the telescope reopened its eye once again, snapping a series of tantalising new images, including one of the iconic galaxy grouping known as Stéphane's Quintet, an image so striking that it became one of the principal five targets of the James Webb Telescope. By 2011, Hubble had made its one millionth observation, firmly cementing its legacy as one of the most successful scientific endeavours of all time. And in the following year, it illustrated this legacy with a third, even deeper rendition of the deep-field image, the Extreme Deep Field, made by compiling almost a decade's worth of observations of a smaller patch of the sky within the Ultra Deep Field. It's revealed more than 5,500 new galaxies, the faintest of which are less than one ten-billionth of the brightness required by the human eye. And in the decade that has followed, Hubble has continued to image the universe from a variety of viewpoints, as the world eagerly awaited the James Webb Telescope. Two years on from the Extreme Deep Field, NASA released the first picture from a new deep-image programme, with the same objective of revealing hidden ancient galaxies, but this time using a different approach. The Frontier Fields were a set of six deep-space images, created by overlaying foreground observations of a dense galaxy cluster atop a series of long exposures of a sparse patch of background space. Because massive gravitational influences, such as those exerted by galaxy clusters, are able to curve the paths of photons, certain clusters can be used as a gravitational lens, for magnifying and elongating the emissions of background galaxies to a degree unattainable with artificial imaging. And in 2014, the first Frontier Field image was released, utilising the 4 billion light-year distant Pandora's Cluster, to enlarge the emissions of more than 3,000 previously hidden ancient galaxies. And two years later, in 2016, Hubble smashed the cosmic distance record when it spotted a far-off but luminous primordial dwarf galaxy, more than 13.3 billion light-years from Earth. This ancient galaxy, dubbed GNZ11 after its redshift value, is thought to have formed a mere 400 million years after the birth of the universe, and remained the most distant object known to humanity for more than half a decade, before being usurped by a stream of new, even farther galaxies spotted by the James Webb Telescope. More and more in the decade of the 2020s, will we see the magnificent achievements of the Hubble Space Telescope, matched and exceeded by the capacities of Webb, whose comprehensive infrared coverage promises a far greater level of detail when studying the farthest corners of space. Nevertheless, Hubble still lies at the forefront of humanity's unending quest to capture a glimpse of the universe. With the earliest time Hubble might cease its operations now estimated to be 2027, who knows what else this extraordinary observatory will teach us, before it closes its eye for the final time.