Sayed Amirudin

Active regions on the Sun combined to look something like a jack-o-lantern’s face on October 8, 2014. The image was captured by NASA's Solar Dynamics Observatory, or SDO, which watches the Sun at all times from its orbit in space.

The active regions in this image appear brighter because those are areas that emit more light and energy. They are markers of an intense and complex set of magnetic fields hovering in the Sun’s atmosphere, the corona. This image blends together two sets of extreme ultraviolet wavelengths at 171 and 193 Ångströms, typically colorized in gold and yellow, to create a particularly Halloween-like appearance.

As the name implies, this reflection nebula associated with the star Rigel looks suspiciously like a fairytale crone. Formally known as IC 2118 in the constellation Orion, the Witch Head Nebula glows primarily by light reflected from the star. The color of this very blue nebula is caused not only by blue color of its star, but also because the dust grains reflect blue light more efficiently than red. A similar physical process causes Earth's daytime sky to appear blue.

Described as a "dusty curtain" or "ghostly apparition," mysterious reflection nebula VdB 152 really is very faint. Far from your neighborhood on this Halloween Night, the cosmic phantom is nearly 1,400 light-years away. Also catalogued as Ced 201, it lies along the northern Milky Way in the royal constellation Cepheus. Near the edge of a large molecular cloud, pockets of interstellar dust in the region block light from background stars or scatter light from the embedded bright star giving parts of the nebula a characteristic blue color. Ultraviolet light from the star is also thought to cause a dim reddish luminescence in the nebular dust. Though stars do form in molecular clouds, this star seems to have only accidentally wandered into the area, as its measured velocity through space is very different from the cloud's velocity. This deep telescopic image of the region spans about 7 light-years.

Countless galaxies vie for attention in this monster image of the Fornax Galaxy Cluster, some appearing only as pinpricks of light while others dominate the foreground. One of these is the lenticular galaxy NGC 1316. The turbulent past of this much-studied galaxy has left it with a delicate structure of loops, arcs and rings that astronomers have now imaged in greater detail than ever before with the VLT Survey Telescope. This astonishingly deep image also reveals a myriad of dim objects along with faint intracluster light.

Captured using the exceptional sky-surveying abilities of the VLT Survey Telescope (VST) at ESO’s Paranal Observatory in Chile, this deep view reveals the secrets of the luminous members of the Fornax Cluster, one of the richest and closest galaxy clusters to the Milky Way. This 2.3-gigapixel image is one of the largest images ever released by ESO.

Perhaps the most fascinating member of the cluster is NGC 1316, a galaxy that has experienced a dynamic history, being formed by the merger of multiple smaller galaxies. The gravitational distortions of the galaxy’s adventurous past have left their mark on its lenticular structure. Large ripples, loops and arcs embedded in the starry outer envelope were first observed in the 1970s, and they remain an active field of study for contemporary astronomers, who use the latest telescope technology to observe the finer details of NGC 1316’s unusual structure through a combination of imaging and modelling.

The mergers that formed NGC 1316 led to an influx of gas, which fuels an exotic astrophysical object at its centre: a supermassive black hole with a mass roughly 150 million times that of the Sun. As it accretes mass from its surroundings, this cosmic monster produces immensely powerful jets of high-energy particles , that in turn give rise to the characteristic lobes of emission seen at radio wavelengths, making NGC 1316 the fourth-brightest radio source in the sky.

NGC 1316 has also been host to four recorded type Ia supernovae, which are vitally important astrophysical events for astronomers. Since type Ia supernovae have a very clearly defined brightness, they can be used to measure the distance to the host galaxy; in this case, 60 million light-years. These “standard candles” are much sought-after by astronomers, as they are an excellent tool to reliably measure the distance to remote objects. In fact, they played a key role in the groundbreaking discovery that our Universe is expanding at an accelerating rate.

This image was taken by the VST at ESO’s Paranal Observatory as part of the Fornax Deep Survey, a project to provide a deep, multi-imaging survey of the Fornax Cluster. The team, led by Enrichetta Iodice (INAF – Osservatorio di Capodimonte, Naples, Italy), have previously observed this area with the VST and revealed a faint bridge of light between NGC 1399 and the smaller galaxy NGC 1387. The VST was specifically designed to conduct large-scale surveys of the sky. With its huge corrected field of view and specially designed 256-megapixel camera, OmegaCAM, the VST can produce deep images of large areas of sky quickly, leaving the much larger telescopes — like ESO’s Very Large Telescope (VLT) — to explore the details of individual objects.

Brilliant blue stars litter the southern sky and the galactic bulge of our home galaxy, the Milky Way, hangs serenely above the horizon in this spectacular shot of ESO’s Paranal Observatory.

This image was taken atop Cerro Paranal in Chile, home to ESO’s Very Large Telescope (VLT). In the foreground, the open dome of one of the four 1.8-metre Auxiliary Telescopes can be seen. The four Auxiliary Telescopes can be utilised together, to form the Very Large Telescope Interferometer (VLTI).

The plane of the Milky Way is dotted with bright regions of hot gas. The very bright star towards the upper left corner of the frame is Antares — the brightest star in Scorpius and the fifteenth brightest star in the night sky.

Stunning views like this image of Saturn's night side are only possible thanks to our robotic emissaries like Cassini. Until future missions are sent to Saturn, Cassini's image-rich legacy must suffice.

Because Earth is closer to the Sun than Saturn, observers on Earth only see Saturn's day side. With spacecraft, we can capture views (and data) that are simply not possible from Earth, even with the largest telescopes.

This view looks toward the sunlit side of the rings from about 7 degrees above the ring plane. The image was taken in visible light with the wide-angle camera on NASA's Cassini spacecraft on June 7, 2017.

The view was obtained at a distance of approximately 751,000 miles (1.21 million kilometers) from Saturn. Image scale is 45 miles (72 kilometers) per pixel.

The Cassini spacecraft ended its mission on September 15, 2017.

During its flight, the Galileo spacecraft returned images of the Moon. The Galileo spacecraft surveyed the Moon on December 7, 1992, on its way to explore the Jupiter system in 1995-1997. The left part of this north pole view is visible from Earth. This color picture is a mosaic assembled from 18 images taken by Galileo's imaging system through a green filter. The left part of this picture shows the dark, lava-filled Mare Imbrium (upper left); Mare Serenitatis (middle left), Mare Tranquillitatis (lower left), and Mare Crisium, the dark circular feature toward the bottom of the mosaic. Also visible in this view are the dark lava plains of the Marginis and Smythii Basins at the lower right. The Humboldtianum Basin, a 650-kilometer (400-mile) impact structure partly filled with dark volcanic deposits, is seen at the center of the image. The Moon's north pole is located just inside the shadow zone, about a third of the way from the top left of the illuminated region.

This NASA/ESA Hubble Space Telescope image is chock-full of galaxies — each glowing speck is a different galaxy, bar the bright flash in the middle of the image which is actually a star lying within our own galaxy that just happened to be in the way. At the centre of the image lies something especially interesting, the centre of the massive galaxy cluster called WHL J24.3324-8.477, including the brightest galaxy of the cluster.

The Universe contains structures on various scales — planets collect around stars, stars collect into galaxies, galaxies collect into groups, and galaxy groups collect into clusters. Galaxy clusters contain hundreds to thousands of galaxies bound together by gravity. Dark matter and dark energy play key roles in the formation and evolution of these clusters, so studying massive galaxy clusters can help scientists to unravel the mysteries of these elusive phenomena.

This infrared image was taken by Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 as part of an observing programme called RELICS (Reionization Lensing Cluster Survey). RELICS imaged 41 massive galaxy clusters with the aim of finding the brightest distant galaxies for the forthcoming NASA/ESA/CSA James Webb Space Telescope (JWST) to study. Such research will tell us more about our cosmic origins.

This color-enhanced image of Jupiter and two of its largest moons -- Io and Europa -- was captured by NASA's Juno spacecraft as it performed its eighth flyby of the gas giant planet.

The image was taken on Sept. 1, 2017 at 3:14 p.m. PDT (6:14 p.m. EDT). At the time the image was taken, the spacecraft was about 17,098 miles (27,516 kilometers) from the tops of the clouds of the planet at a latitude of minus 49.372 degrees.

Closer to the planet, the Galilean moon of Io can be seen at an altitude of 298,880 miles (481,000 kilometers) and at a spatial scale of 201 miles (324 kilometers) per pixel. In the distance (to the left), another one of Jupiter's Galilean moons, Europa, is visible at an altitude of 453,601 miles (730,000 kilometers) and at a spatial scale of 305 miles (492 kilometers) per pixel.

New NASA research is helping to refine our understanding of candidate planets beyond our Solar System that might support life.

“Using a model that more realistically simulates atmospheric conditions, we discovered a new process that controls the habitability of exoplanets and will guide us in identifying candidates for further study,” said Yuka Fujii of NASA’s Goddard Institute for Space Studies (GISS), New York, New York and the Earth-Life Science Institute at the Tokyo Institute of Technology, Japan.

Previous models simulated atmospheric conditions along one dimension, the vertical. Like some other recent habitability studies, the new research used a model that calculates conditions in all three dimensions, allowing the team to simulate the circulation of the atmosphere and the special features of that circulation, which one-dimensional models cannot do. The new work will help astronomers allocate scarce observing time to the most promising candidates for habitability.

Liquid water is necessary for life as we know it, so the surface of an alien world (e.g. an exoplanet) is considered potentially habitable if its temperature allows liquid water to be present for sufficient time (billions of years) to allow life to thrive. If the exoplanet is too far from its parent star, it will be too cold, and its oceans will freeze. If the exoplanet is too close, light from the star will be too intense, and its oceans will eventually evaporate and be lost to space. This happens when water vapor rises to a layer in the upper atmosphere called the stratosphere and gets broken into its elemental components (hydrogen and oxygen) by ultraviolet light from the star. The extremely light hydrogen atoms can then escape to space. Planets in the process of losing their oceans this way are said to have entered a “moist greenhouse” state because of their humid stratospheres.

In order for water vapor to rise to the stratosphere, previous models predicted that long-term surface temperatures had to be greater than anything experienced on Earth – over 150 degrees Fahrenheit (66 degrees Celsius). These temperatures would power intense convective storms; however, it turns out that these storms aren’t the reason water reaches the stratosphere for slowly rotating planets entering a moist greenhouse state.

“We found an important role for the type of radiation a star emits and the effect it has on the atmospheric circulation of an exoplanet in making the moist greenhouse state,” said Fujii. For exoplanets orbiting close to their parent stars, a star’s gravity will be strong enough to slow a planet’s rotation. This may cause it to become tidally locked, with one side always facing the star – giving it eternal day – and one side always facing away –giving it eternal night.

When this happens, thick clouds form on the dayside of the planet and act like a sun umbrella to shield the surface from much of the starlight. While this could keep the planet cool and prevent water vapor from rising, the team found that the amount of near-Infrared radiation (NIR) from a star could provide the heat needed to cause a planet to enter the moist greenhouse state. NIR is a type of light invisible to the human eye. Water as vapor in air and water droplets or ice crystals in clouds strongly absorbs NIR light, warming the air. As the air warms, it rises, carrying the water up into the stratosphere where it creates the moist greenhouse.

This process is especially relevant for planets around low-mass stars that are cooler and much dimmer than the Sun. To be habitable, planets must be much closer to these stars than our Earth is to the Sun. At such close range, these planets likely experience strong tides from their star, making them rotate slowly. Also, the cooler a star is, the more NIR it emits. The new model demonstrated that since these stars emit the bulk of their light at NIR wavelengths, a moist greenhouse state will result even in conditions comparable to or somewhat warmer than Earth's tropics. For exoplanets closer to their stars, the team found that the NIR-driven process increased moisture in the stratosphere gradually. So, it’s possible, contrary to old model predictions, that an exoplanet closer to its parent star could remain habitable.

This is an important observation for astronomers searching for habitable worlds, since low-mass stars are the most common in the galaxy. Their sheer numbers increase the odds that a habitable world may be found among them, and their small size increases the chance to detect planetary signals.

The new work will help astronomers screen the most promising candidates in the search for planets that could support life. “As long as we know the temperature of the star, we can estimate whether planets close to their stars have the potential to be in the moist greenhouse state,” said Anthony Del Genio of GISS. “Current technology will be pushed to the limit to detect small amounts of water vapor in an exoplanet’s atmosphere. If there is enough water to be detected, it probably means that planet is in the moist greenhouse state.”

In this study, researchers assumed a planet with an atmosphere like Earth, but entirely covered by oceans. These assumptions allowed the team to clearly see how changing the orbital distance and type of stellar radiation affected the amount of water vapor in the stratosphere. In the future, the team plans to vary planetary characteristics such as gravity, size, atmospheric composition, and surface pressure to see how they affect water vapor circulation and habitability.

The elliptical galaxy NGC 4993 is located about 130 million light-years from Earth. On 17 August 2017 the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo Interferometer both detected gravitational waves from the collision of two neutron stars within this galaxy. The event also resulted in a flare of light, called a kilonova, which is visible to the upper left of the galactic centre in this image from the NASA/ESA Hubble Space Telescope.

Fomalhaut is one of the brightest stars in the sky. At roughly 25 light-years away the star lies especially close to us, and can be seen shining brightly in the constellation of Piscis Austrinus (The Southern Fish). This image from the Atacama Large Millimeter/submillimeter Array (ALMA) shows Fomalhaut (centre) encircled by a ring of dusty debris — this is the first time this scene has been captured at such high resolution and sensitivity at millimetre wavelengths.

Fomalhaut’s disc comprises a mix of cosmic dust and gas from comets in the Fomalhaut system (exocomets), released as the exocomets graze past and smash into one another. This turbulent environment resembles an early period in our own Solar System known as the Late Heavy Bombardment, which occurred approximately four billions years ago. This era saw huge numbers of rocky objects hurtle into the inner Solar System and collide with the young terrestrial planets, including Earth, where they formed a myriad of impact craters — many of which remain visible today on the surfaces of planets such as Mercury and Mars.

Fomalhaut is known to be surrounded by several discs of debris — the one visible in this ALMA image is the outermost one. The ring is approximately 20 billion kilometers from the central star and about 2 billion kilometers wide. Such a relative narrow, eccentric disc can only be produced by the gravitational influence of planets in the system, like Jupiter’s gravitational influence on our asteroid belt. In 2008 the NASA/ESA Hubble Space Telescope discovered the famous exoplanet Fomalhaut b orbiting within this belt, but the planet is not visible in this ALMA image.

Looking up at the Moon at night, Earth’s closest neighbor appears in shades of gray and white; a dry desert in the vacuum of space, inactive and dead for billions of years. Like many things, though, with the Moon, there is so much more than what meets the eye.

Research completed by NASA Marshall Space Flight Center planetary volcanologist Debra Needham in Huntsville, Alabama, and planetary scientist David Kring at the Lunar and Planetary Institute in Houston, Texas, suggests that billions of years ago, the Moon actually had an atmosphere. The ancient lunar atmosphere was thicker than the atmosphere of Mars today and was likely capable of weathering rocks and producing windstorms. Perhaps most importantly, it could be a source for some, if not all, of the water detected on the Moon.

“It just completely changes the way we think of the Moon,” said Needham, a scientist in Marshall’s Science and Technology Office. “It becomes a much more dynamic planetary body to explore.”

Discovering the existence, thickness and composition of the atmosphere began with understanding how much lava erupted on the Moon 3.9 to one billion years ago, forming the lava plains we see as the dark areas on the surface of the Moon today. Needham and Kring then used lab analyses of lunar basalts -- iron and magnesium-rich volcanic rocks -- returned to Earth by the Apollo crews to estimate the amounts and composition of gases -- also called volatiles -- released during those volcanic eruptions.

The short-lived atmosphere -- estimated to have lasted approximately 70 million years -- was comprised primarily of carbon monoxide, sulfur and water. As volcanic activity declined, the release of the gases also declined. What atmosphere existed was either lost to space or became part of the surface of the Moon.

The researchers discovered that so much water was released during the eruptions -- potentially three times the amount of water in the Chesapeake Bay -- that if 0.1 percent of the erupted water migrated to the permanently shadowed regions on the Moon, it could account for all of the water detected there.

“We’re suggesting that internally-sourced volatiles might be at least contributing factors to these potential in-situ resource utilization deposits,” Needham said.

Water is one of the keys to living off of the land in space, also called in-situ resource utilization (ISRU). Knowing where the water came from helps scientists and mission planners alike know if the resource is renewable. Ultimately, more research is needed to determine the exact sources.

The first indication of water on the Moon came in 1994 when NASA’s Clementine spacecraft detected potential signatures of water-ice in the lunar poles. In 1998, NASA’s Lunar Prospector mission detected enhanced hydrogen signatures but could not definitely associate them to water. Ten years later, NASA’s Lunar Reconnaissance Orbiter and its partner spacecraft, the Lunar CRater Observation and Sensing Satellite (LCROSS), definitively confirmed the presence of water on the Moon. That same year, in 2008, volcanic glass beads brought back from the Moon by the Apollo 15 and 17 crews were discovered to contain volatiles, including water, leading to the research that indicates the Moon once had a significant atmosphere and was once much different than what we see today.

Casting one’s eyes at the Moon or viewing it through a telescope, the surface of the Moon today gives but a glimpse into its dynamic and complex history. Recent findings that propose Earth’s neighbor once had an atmosphere comparable to Mars’ continue to unravel the lunar past, while prompting scientists and explorers to ask more questions about Earth’s mysterious companion in the Solar System.

This illustration shows the hot, dense, expanding cloud of debris stripped from two neutron stars just before they collided. Within this neutron-rich debris, large quantities of some of the universe's heaviest elements were forged, including hundreds of Earth masses of gold and platinum.

This represents the first time scientists detected light tied to a gravitational-wave event, thanks to two merging neutron stars in the galaxy NGC 4993, located about 130 million light-years from Earth in the constellation Hydra.

This image, captured by the NASA/ESA Hubble Space Telescope, shows what happens when two galaxies become one. The twisted cosmic knot seen here is NGC 2623 — or Arp 243 — and is located about 250 million light-years away in the constellation of Cancer (The Crab).

NGC 2623 gained its unusual and distinctive shape as the result of a major collision and subsequent merger between two separate galaxies. This violent encounter caused clouds of gas within the two galaxies to become compressed and stirred up, in turn triggering a sharp spike of star formation. This active star formation is marked by speckled patches of bright blue; these can be seen clustered both in the centre and along the trails of dust and gas forming NGC 2623’s sweeping curves (known as tidal tails). These tails extend for roughly 50 000 light-years from end to end. Many young, hot, newborn stars form in bright stellar clusters — at least 170 such clusters are known to exist within NGC 2623.

NGC 2623 is in a late stage of merging. It is thought that the Milky Way will eventually resemble NGC 2623 when it collides with our neighbouring galaxy, the Andromeda Galaxy, in four billion years time.

In contrast to the image of NGC 2623 released in 2009, this new version contains data from recent narrow-band and infrared observations that make more features of the galaxy visible.

The NASA/ESA Hubble Space Telescope has observed for the first time the source of a gravitational wave, created by the merger of two neutron stars. This merger created a kilonova — an object predicted by theory decades ago — that ejects heavy elements such as gold and platinum into space. This event also provides the strongest evidence yet that short duration gamma-ray bursts are caused by mergers of neutron stars. This discovery is the first glimpse of multi-messenger astronomy, bringing together both gravitational waves and electromagnetic radiation.

On 17 August 2017 the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo Interferometer both alerted astronomical observers all over the globe about the detection of a gravitational wave event named GW170817. About two seconds after the detection of the gravitational wave, ESA’s INTEGRAL telescope and NASA’s Fermi Gamma-ray Space Telescope observed a short gamma-ray burst in the same direction.

In the night following the initial discovery, a fleet of telescopes started their hunt to locate the source of the event. Astronomers found it in the lenticular galaxy NGC 4993, about 130 million light-years away. A point of light was shining where nothing was visible before and this set off one of the largest multi-telescope observing campaigns ever — among these telescopes was the NASA/ESA Hubble Space Telescope.

Several different teams of scientists used Hubble over the two weeks following the gravitational wave event alert to observe NGC 4993. Using Hubble’s high-resolution imaging capabilities they managed to get the first observational proof for a kilonova, the visible counterpart of the merging of two extremely dense objects — most likely two neutron stars. Such mergers were first suggested more than 30 years ago but this marks the first firm observation of such an event. The distance to the merger makes the source both the closest gravitational wave event detected so far and also one of the closest gamma-ray burst sources ever seen.

“Once I saw that there had been a trigger from LIGO and Virgo at the same time as a gamma-ray burst I was blown away,” recalls Andrew Levan of the University of Warwick, who led the Hubble team that obtained the first observations. “When I realised that it looked like neutron stars were involved, I was even more amazed. We’ve been waiting a long time for an opportunity like this!”

Hubble captured images of the galaxy in visible and infrared light, witnessing a new bright object within NGC 4993 that was brighter than a nova but fainter than a supernova. The images showed that the object faded noticeably over the six days of the Hubble observations. Using Hubble’s spectroscopic capabilities the teams also found indications of material being ejected by the kilonova as fast as one-fifth of the speed of light.

“It was surprising just how closely the behaviour of the kilonova matched the predictions,” said Nial Tanvir, professor at the University of Leicester and leader of another Hubble observing team. “It looked nothing like known supernovae, which this object could have been, and so confidence was soon very high that this was the real deal.”

Connecting kilonovae and short gamma-ray bursts to neutron star mergers has so far been difficult, but the multitude of detailed observations following the detection of the gravitational wave event GW170817 has now finally verified these connections.

“The spectrum of the kilonova looked exactly like how theoretical physicists had predicted the outcome of the merger of two neutron stars would appear,” says Levan. “It ties this object to the gravitational wave source beyond all reasonable doubt.”

The infrared spectra taken with Hubble also showed several broad bumps and wiggles that signal the formation of some of the heaviest elements in nature. These observations may help solve another long-standing question in astronomy: the origin of heavy chemical elements, like gold and platinum. In the merger of two neutron stars, the conditions appear just right for their production.

The implications of these observations are immense. As Tanvir explains: “This discovery has opened up a new approach to astronomical research, where we combine information from both electromagnetic light and from gravitational waves. We call this multi-messenger astronomy — but until now it has just been a dream!”

Levan concludes: “Now, astronomers won’t just look at the light from an object, as we’ve done for hundreds of years, but also listen to it. Gravitational waves provide us with complementary information from objects which are very hard to study using only electromagnetic waves. So pairing gravitational waves with electromagnetic radiation will help astronomers understand some of the most extreme events in the Universe.”

NASA astronaut Joe Acaba photographed Puerto Rico from the cupola of the International Space Station on October 12, 2017.

Acaba, whose parents were both born in Puerto Rico, joined NASA as a member of the 2004 class of astronauts and is on his third mission to the space station as a Flight Engineer on the Expedition 53/54 crew.

This image from the Atacama Large Millimeter/submillimeter Array (ALMA) shows V1247 Orionis, a young, hot star surrounded by a dynamic ring of gas and dust, known as a circumstellar disc. This disc can be seen here in two parts: a clearly defined central ring of matter and a more delicate crescent structure located further out.

The region between the ring and crescent, visible as a dark strip, is thought to be caused by a young planet carving its way through the disc. As the planet orbits around its parent star, its motion creates areas of high pressure on either side of its path, similar to how a ship creates bow waves as it cuts through water. These areas of high pressure could become protective barriers around sites of planet formation; dust particles are trapped within them for millions of years, allowing them the time and space to clump together and grow.

The exquisite resolution of ALMA allows astronomers to study the intricate structure of such a dust trapping vortex for the first time. The image reveals not only the crescent-shaped dust trap at the outer edge of the dark strip, but also regions of excess dust within the ring, possibly indicating a second dust trap that formed inside of the potential planet’s orbit. This confirms the predictions of earlier computer simulations.

Dust trapping is one potential solution to a major stumbling block in current theories of how planets form, which predicts that particles should drift into the central star and be destroyed before they have time to grow to planetesimal sizes (the radial drift problem).

ESO’s fleet of telescopes in Chile have detected the first visible counterpart to a gravitational wave source. These historic observations suggest that this unique object is the result of the merger of two neutron stars. The cataclysmic aftermaths of this kind of merger — long-predicted events called kilonovae — disperse heavy elements such as gold and platinum throughout the Universe. This discovery also provides the strongest evidence yet that short-duration gamma-ray bursts are caused by mergers of neutron stars.

For the first time ever, astronomers have observed both gravitational waves and light (electromagnetic radiation) from the same event, thanks to a global collaborative effort and the quick reactions of both ESO’s facilities and others around the world.

On 17 August 2017 the NSF's Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States, working with the Virgo Interferometer in Italy, detected gravitational waves passing the Earth. This event, the fifth ever detected, was named GW170817. About two seconds later, two space observatories, NASA’s Fermi Gamma-ray Space Telescope and ESA’s INTErnational Gamma Ray Astrophysics Laboratory (INTEGRAL), detected a short gamma-ray burst from the same area of the sky.

The LIGO–Virgo observatory network positioned the source within a large region of the southern sky, the size of several hundred full Moons and containing millions of stars. As night fell in Chile many telescopes peered at this patch of sky, searching for new sources. These included ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA) and VLT Survey Telescope (VST) at the Paranal Observatory, the Italian Rapid Eye Mount (REM) telescope at ESO’s La Silla Observatory, the LCO 0.4-meter telescope at Las Cumbres Observatory, and the American DECam at Cerro Tololo Inter-American Observatory. The Swope 1-metre telescope was the first to announce a new point of light. It appeared very close to NGC 4993, a lenticular galaxy in the constellation of Hydra, and VISTA observations pinpointed this source at infrared wavelengths almost at the same time. As night marched west across the globe, the Hawaiian island telescopes Pan-STARRS and Subaru also picked it up and watched it evolve rapidly.

“There are rare occasions when a scientist has the chance to witness a new era at its beginning,” said Elena Pian, astronomer with INAF, Italy. “This is one such time!”

ESO launched one of the biggest ever “target of opportunity” observing campaigns and many ESO and ESO-partnered telescopes observed the object over the weeks following the detection. ESO’s Very Large Telescope (VLT), New Technology Telescope (NTT), VST, the MPG/ESO 2.2-metre telescope, and the Atacama Large Millimeter/submillimeter Array (ALMA) all observed the event and its after-effects over a wide range of wavelengths. About 70 observatories around the world also observed the event, including the NASA/ESA Hubble Space Telescope.

Distance estimates from both the gravitational wave data and other observations agree that GW170817 was at the same distance as NGC 4993, about 130 million light-years from Earth. This makes the source both the closest gravitational wave event detected so far and also one of the closest gamma-ray burst sources ever seen.

The ripples in spacetime known as gravitational waves are created by moving masses, but only the most intense, created by rapid changes in the speed of very massive objects, can currently be detected. One such event is the merging of neutron stars, the extremely dense, collapsed cores of high-mass stars left behind after supernovae. These mergers have so far been the leading hypothesis to explain short gamma-ray bursts. An explosive event 1000 times brighter than a typical nova — known as a kilonova — is expected to follow this type of event.

The almost simultaneous detections of both gravitational waves and gamma rays from GW170817 raised hopes that this object was indeed a long-sought kilonova and observations with ESO facilities have revealed properties remarkably close to theoretical predictions. Kilonovae were suggested more than 30 years ago but this marks the first confirmed observation.

Following the merger of the two neutron stars, a burst of rapidly expanding radioactive heavy chemical elements left the kilonova, moving as fast as one-fifth of the speed of light. The colour of the kilonova shifted from very blue to very red over the next few days, a faster change than that seen in any other observed stellar explosion.

“When the spectrum appeared on our screens I realised that this was the most unusual transient event I’d ever seen,” remarked Stephen Smartt, who led observations with ESO’s NTT as part of the extended Public ESO Spectroscopic Survey of Transient Objects (ePESSTO) observing programme. “I had never seen anything like it. Our data, along with data from other groups, proved to everyone that this was not a supernova or a foreground variable star, but was something quite remarkable.”

Spectra from ePESSTO and the VLT’s X-shooter instrument suggest the presence of caesium and tellurium ejected from the merging neutron stars. These and other heavy elements, produced during the neutron star merger, would be blown into space by the subsequent kilonova. These observations pin down the formation of elements heavier than iron through nuclear reactions within high-density stellar objects, known as r-process nucleosynthesis, something which was only theorised before.

“The data we have so far are an amazingly close match to theory. It is a triumph for the theorists, a confirmation that the LIGO–VIRGO events are absolutely real, and an achievement for ESO to have gathered such an astonishing data set on the kilonova,” adds Stefano Covino.

“ESO’s great strength is that it has a wide range of telescopes and instruments to tackle big and complex astronomical projects, and at short notice. We have entered a new era of multi-messenger astronomy!” concludes Andrew Levan.

This image from the VIMOS instrument on ESO’s Very Large Telescope at the Paranal Observatory in Chile shows the galaxy NGC 4993, about 130 million light-years from Earth. The galaxy is not itself unusual, but it contains something never before witnessed, the aftermath of the explosion of a pair of merging neutron stars, a rare event called a kilonova (seen just above and slightly to the left of the centre of the galaxy). This merger also produced gravitational waves and gamma rays, both of which were detected by LIGO-Virgo and Fermi/INTEGRAL respectively.

This image from the MUSE instrument on ESO’s Very Large Telescope at the Paranal Observatory in Chile shows the galaxy NGC 4993, about 130 million light-years from Earth. The galaxy is not itself unusual, but it contains something never before witnessed, the aftermath of the explosion of a pair of merging neutron stars, a rare event called a kilonova (seen just above and slightly to the left of the centre of the galaxy). This merger also produced gravitational waves and gamma rays, both of which were detected by LIGO-Virgo and Fermi/INTEGRAL respectively. By also creating a spectrum for each part of the object MUSE allows the emission from glowing gas to be seen, which appears in red here and reveals a surprising spiral structure.

Image obtained by ESO's Gamma-ray Burst Optical/Near-infrared Detector (GROND) attached to the MPG/ESO 2.2-metre telescope at La Silla Observatory.

This image from the VST telescope at ESO's Paranal Observatory in Chile shows the galaxy NGC 4993, about 130 million light-years from Earth. The galaxy is not itself unusual, but it contains something never before witnessed, the aftermath of the explosion of a pair of merging neutron stars, a rare event called a kilonova (seen just above and slightly to the left of the centre of the galaxy). This merger also produced gravitational waves and gamma rays, both of which were detected by LIGO-Virgo and Fermi/INTEGRAL respectively.

This wide-field image generated from the Digitized Sky Survey 2 shows the sky around the galaxy NGC 4993. This galaxy was the host to a merger between two neutron stars, which led to a gravitational wave detection, a short gamma-ray burst and an optical identification of a kilonova event.

The Copernicus Sentinel-3A satellite captured this image of smoke from wildfires in the US state of California on 9 October 2017.

Wildfires broke out in parts of the state on 8 October 2017 around Napa Valley, and the smoke was spread by strong northeasterly winds.

At a distance of about 20,000 light years, G292.0+1.8 is one of only three supernova remnants in the Milky Way known to contain large amounts of oxygen. These oxygen-rich supernovas are of great interest to astronomers because they are one of the primary sources of the heavy elements (that is, everything other than hydrogen and helium) necessary to form planets and people. The X-ray image from Chandra shows a rapidly expanding, intricately structured, debris field that contains, along with oxygen (yellow and orange), other elements such as magnesium (green) and silicon and sulfur (blue) that were forged in the star before it exploded.

This graphic shows two of five new pairs of supermassive black holes recently identified by astronomers using a combination of data from NASA's Chandra X-ray Observatory, the Wide-Field Infrared Survey Explorer (WISE), the ground-based Large Binocular Telescope in Arizona, and the Sloan Digital Sky Survey (SDSS) Mapping Nearby Galaxies at APO (MaNGA) survey. This discovery could help astronomers better understand how giant black holes grow and how they may produce the strongest gravitational wave signals in the Universe.

Each pair contains two supermassive black holes weighing millions of times the mass of the Sun. These black hole couples formed when two galaxies collided and merged with each other, forcing their supermassive black holes close together. While theoretical models have predicted such giant growing black hole pairings should be relatively abundant, they have been difficult to find.

To uncover these latest supermassive black hole pairs, astronomers used optical data from the Sloan Digital Sky Survey (SDSS) — shown in the main panel of each image — to identify galaxies where it appeared that a merger between two smaller galaxies was underway. Next, they selected objects where the separation between the centers of the two galaxies in the SDSS data is less than 30,000 light years, and the infrared colors from WISE data match those predicted for a rapidly growing supermassive black hole.

Seven merging systems containing at least one supermassive black hole were found with this technique. Because strong X-ray emission is a hallmark of growing supermassive black holes, the team then observed these systems with Chandra. They found that five systems contained pairs of X-ray sources that were separated by a relatively small distance (see inset for two examples), providing compelling evidence that they contain two growing, or feeding, supermassive black holes.

Both the X-ray data from Chandra and the infrared WISE observations suggest that the supermassive black holes are buried in large amounts of dust and gas. Because these two wavelengths are able to penetrate the obscuring clouds, this makes the combination of infrared selection with X-ray follow-up a very effective way to find these black hole pairs. Chandra's sharp vision is also critical as it is able to resolve each of the X-ray sources in the pairs.

This image, captured by ESO’s Very Large Telescope (VLT) at Paranal, shows a small part of the well-known emission nebula, NGC 6357, located some 8000 light-years away, in the tail of the southern constellation of Scorpius (The Scorpion). The image glows with the characteristic red of an H II region, and contains a large amount of ionised and excited hydrogen gas.

The cloud is bathed in intense ultraviolet radiation — mainly from the open star cluster Pismis 24, home to some massive, young, blue stars — which it re-emits as visible light, in this distinctive red hue.

The cluster itself is out of the field of view of this picture, its diffuse light seen illuminating the cloud on the centre-right of the image. We are looking at a close-up of the surrounding nebula, showing a mesh of gas, dark dust, and newly born and still forming stars.

As far as galaxies are concerned, size can be deceptive. Some of the largest galaxies in the Universe are dormant, while some dwarf galaxies, such as ESO 553-46 imaged here by the NASA/ESA Hubble Space Telescope, can produce stars at a hair-raising rate. In fact, ESO 553-46 has one of the highest rates of star formation of the 1000 or so galaxies nearest to the Milky Way. No mean feat for such a diminutive galaxy!

Clusters of young, hot stars are speckling the galaxy, burning with a fierce blue glow. The intense radiation they produce also causes surrounding gas to light up, which is bright red in this image. The small mass and distinctive colouring of galaxies of this type prompted astronomers to classify them, appropriately, as blue compact dwarfs (BCD).

Lacking the clear core and structure that many larger galaxies — such as the Milky Way — have, BCDs such as ESO 553-46 are composed of many large clusters of stars bound together by gravity. Their chemical makeup is interesting to astronomers, since they contain relatively little dust and few elements heavier than helium, which are produced in stars and distributed via supernova explosions. Such conditions are strikingly similar to those that existed in the early Universe, when the first galaxies were beginning to form.

This illustration depicts a hypothetical uneven ring of dust orbitingKIC 8462852, also known as Boyajians Star or Tabby's Star. Astronomers have found the dimming of the star over long periods appears to be weaker at longer infrared wavelengths of light and stronger at shorter ultraviolet wavelengths. Such reddening is characteristic of dust particles and inconsistent with more fanciful alien megastructure concepts, which would evenly dim all wavelengths of light.

By studying observations from NASAsSpitzer and Swift telescopes, as well as the Belgian AstroLAB IRIS observatory, the researchers have been able to better constrain the size of the dust particles. This places them within the range found in dust disks orbiting stars, and larger than the particles typically found in interstellar dust.

The system is portrayed with a couple of comets, consistent with previous studies that have found evidence for cometary activity within the system.

The 4 Laser Guide Star Facility (4LGSF), a new subsystem of the Adaptive Optics Facility (AOF) on UT4 of the Very Large Telescope (VLT), at ESO's Paranal Observatory in Chile. The facility saw first light in April 2016 and is the most powerful laser guide star system in the world. The image was taken by ESO Photo Ambassador Juan Carlos Muñoz-Mateos.

This vibrant image from NASA's Spitzer Space Telescope shows the Large Magellanic Cloud, a satellite galaxy to our own Milky Way galaxy.

The infrared image, a mosaic of 300,000 individual tiles, offers astronomers a unique chance to study the lifecycle of stars and dust in a single galaxy. Nearly one million objects are revealed for the first time in this Spitzer view, which represents about a 1,000-fold improvement in sensitivity over previous space-based missions. Most of the new objects are dusty stars of various ages populating the Large Magellanic Cloud; the rest are thought to be background galaxies.

The blue color in the picture, seen most prominently in the central bar, represents starlight from older stars. The chaotic, bright regions outside this bar are filled with hot, massive stars buried in thick blankets of dust. The red color around these bright regions is from dust heated by stars, while the red dots scattered throughout the picture are either dusty, old stars or more distant galaxies. The greenish clouds contain cooler interstellar gas and molecular-sized dust grains illuminated by ambient starlight.

Astronomers say this image allows them to quantify the process by which space dust the same stuff that makes up planets and even people is recycled in a galaxy. The picture shows dust at its three main cosmic hangouts: around the young stars, where it is being consumed (red-tinted, bright clouds); scattered about in the space between stars (greenish clouds); and in expelled shells of material from old stars (randomly-spaced red dots).

The Large Magellanic Cloud, located 160,000 light-years from Earth, is one of a handful of dwarf galaxies that orbit our own Milky Way. It is approximately one-third as wide as the Milky Way, and, if it could be seen in its entirety, would cover the same amount of sky as a grid of about 480 full moons. About one-third of the entire galaxy can be seen in the Spitzer image.

This picture is a composite of infrared light captured by Spitzer. Light with wavelengths of 3.6 (blue) and 8 (green) microns was captured by the telescope's infrared array camera; 24-micron light (red) was detected by the multiband imaging photometer.

This striking image of Jupiter was captured by NASA's Juno spacecraft as it performed its eighth flyby of the gas giant planet.

The image was taken on September 1, 2017 at 2:58 p.m. PDT (5:58 p.m. EDT). At the time the image was taken, the spacecraft was 4,707 miles (7,576 kilometers) from the tops of the clouds of the planet at a latitude of about -17.4 degrees.

The spectacular aurora borealis, or the “northern lights,” over Canada is sighted from the International Space Station near the highest point of its orbital path. The station’s main solar arrays are seen in the left foreground. This photograph was taken by a member of the Expedition 53 crew aboard the station on September 15, 2017.

This Hubble Space Telescope image shows a fuzzy cloud of dust, called a coma, surrounding the comet C/2017 K2 PANSTARRS (K2), the farthest active comet ever observed entering the solar system. Hubble snapped images of K2 when the frozen visitor was over 2.4 billion kilometres from the Sun, just beyond Saturn's orbit. Even at that remote distance, sunlight is warming the frigid comet, producing a 128,000-kilometre-wide coma that envelops a tiny, solid nucleus. K2 has been traveling for millions of years from its home in the Oort Cloud, a spherical region at the edge of our solar system. This frigid area contains hundreds of billions of comets, the icy leftovers from the formation of the solar system 4.6 billion years ago. The image was taken in June 2017 by Hubble's Wide Field Camera 3.

Despite the advances made in past decades, the process of galaxy formation remains an open question in astronomy. Various theories have been suggested, but since galaxies come in all shapes and sizes — including elliptical, spiral, and irregular — no single theory has so far been able to satisfactorily explain the origins of all the galaxies we see throughout the Universe.

To determine which formation model is correct (if any), astronomers hunt for the telltale signs of various physical processes. One example of this is galactic coronas, which are huge, invisible regions of hot gas that surround a galaxy’s visible bulk, forming a spheroidal shape. They are so hot that they can be detected by their X-ray emission, far beyond the optical radius of the galaxy. Because they are so wispy, these coronas are extremely difficult to detect. In 2013, astronomers highlighted NGC 6753, imaged here by the NASA/ESA Hubble Space Telescope, as one of only two known spiral galaxies that were both massive enough and close enough to permit detailed observations of their coronas. Of course, NGC 6753 is only close in astronomical terms — the galaxy is nearly 150 million light-years from Earth.

NGC 6753 is a whirl of colour in this image — the bursts of blue throughout the spiral arms are regions filled with young stars glowing brightly in ultraviolet light, while redder areas are filled with older stars emitting in the cooler near-infrared.

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This spectacular spiral galaxy, known as NGC 1964, resides approximately 70 million light-years away in the constellation of Lepus (The Hare). NGC 1964 has a bright and dense core. This core sits within a mottled oval disc, which is itself encircled by distinct spiral arms speckled with bright starry regions. The brilliant centre of the galaxy caught the eye of the astronomer William Herschel on the night of 20 November 1784, leading to the galaxy’s discovery and subsequent documentation in the New General Catalogue.

In addition to containing stars, NGC 1964 lives in a star-sprinkled section of the sky. In this view from the Wide Field Imager (WFI) — an instrument mounted on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory, Chile — the star HD 36785 can be seen to the galaxy’s immediate right. Above it reside two other prominent stars named HD 36784 and TYC 5928-368-1 — and the large bright star below NGC 1964 is known as BD-22 1147.

This view of NGC 1964 also contains an array of galaxies, visible in the background. The WFI is able to observe the light from these distant galaxies, and those up to 40 million times fainter than the human eye can see.

At a distance of just 160 000 light-years, the Large Magellanic Cloud (LMC) is one of the Milky Way’s closest companions. It is also home to one of the largest and most intense regions of active star formation known to exist anywhere in our galactic neighbourhood — the Tarantula Nebula. This NASA/ESA Hubble Space Telescope image shows both the spindly, spidery filaments of gas that inspired the region’s name, and the intriguing structure of stacked “bubbles” that forms the so-called Honeycomb Nebula (to the lower left).

The Honeycomb Nebula was found serendipitously by astronomers using ESO’s New Technology Telescope to image the nearby SN1987A, the closest observed supernova to Earth for over 400 years. The nebula’s strange bubble-like shape has baffled astronomers since its discovery in the early 1990s. Various theories have been proposed to explain its unique structure, some more exotic than others.

In 2010, a group of astronomers studied the nebula and, using advanced data analysis and computer modelling, came to the conclusion that its unique appearance is likely due to the combined effect of two supernovae — a more recent explosion has pierced the expanding shell of material created by an older explosion. The nebula’s especially striking appearance is suspected to be due to a fortuitous viewing angle; the honeycomb effect of the circular shells may not be visible from another viewpoint.

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