Herschel Finds Oceans of Water in Disk of Nearby Star

Using data from the Herschel Space Observatory, astronomers have detected for the first time cold water vapor enveloping a dusty disk around a young star. The findings suggest that this disk, which is poised to develop into a solar system, contains great quantities of water, suggesting that water-covered planets like Earth may be common in the universe. Herschel is a European Space Agency mission with important NASA contributions.

Scientists previously found warm water vapor in planet-forming disks close to a central star. Evidence for vast quantities of water extending out into the cooler, far reaches of disks where comets take shape had not been seen until now. The more water available in disks for icy comets to form, the greater the chances that large amounts eventually will reach new planets through impacts.

"Our observations of this cold vapor indicate enough water exists in the disk to fill thousands of Earth oceans," said astronomer Michiel Hogerheijde of Leiden Observatory in The Netherlands. Hogerheijde is the lead author of a paper describing these findings in the Oct. 21 issue of the journal Science.

The star with this waterlogged disk, called TW Hydrae, is 10 million years old and located about 175 light-years away from Earth, in the constellation Hydra. The frigid, watery haze detected by Hogerheijde and his team is thought to originate from ice-coated grains of dust near the disk's surface. Ultraviolet light from the star causes some water molecules to break free of this ice, creating a thin layer of gas with a light signature detected by Herschel's Heterodyne Instrument for the Far-Infrared, or HIFI.

"These are the most sensitive HIFI observations to date," said Paul Goldsmith, NASA project scientist for the Herschel Space Observatory at the agency's Jet Propulsion Laboratory in Pasadena, Calif. "It is a testament to the instrument builders that such weak signals can be detected."

TW Hydrae is an orange dwarf star, somewhat smaller and cooler than our yellow-white sun. The giant disk of material that encircles the star has a size nearly 200 times the distance between Earth and the sun. Over the next few million years, astronomers believe matter within the disk will collide and grow into planets, asteroids and other cosmic bodies. Dust and ice particles will assemble as comets.

As the new solar system evolves, icy comets are likely to deposit much of the water they contain on freshly created worlds through impacts, giving rise to oceans. Astronomers believe TW Hydrae and its icy disk may be representative of many other young star systems, providing new insights on how planets with abundant water could form throughout the universe.

Our Galaxy Might Hold Thousands of Ticking "Time Bombs"

Cambridge, MA - In the Hollywood blockbuster "Speed," a bomb on a bus is rigged to blow up if the bus slows down below 50 miles per hour. The premise - slow down and you explode - makes for a great action movie plot, and also happens to have a cosmic equivalent.

New research shows that some old stars might be held up by their rapid spins, and when they slow down, they explode as supernovae. Thousands of these "time bombs" could be scattered throughout our Galaxy.

"We haven't found one of these 'time bomb' stars yet in the Milky Way, but this research suggests that we've been looking for the wrong signs. Our work points to a new way of searching for supernova precursors," said astrophysicist Rosanne Di Stefano of the Harvard-Smithsonian Center for Astrophysics (CfA).

The specific type of stellar explosion Di Stefano and her colleagues studied is called a Type Ia supernova. It occurs when an old, compact star known as a white dwarf destabilizes.

A white dwarf is a stellar remnant that has ceased nuclear fusion. It typically can weigh up to 1.4 times as much as our Sun - a figure called the Chandrasekhar mass after the astronomer who first calculated it. Any heavier, and gravity overwhelms the forces supporting the white dwarf, compacting it and igniting runaway nuclear fusion that blows the star apart.

There are two possible ways for a white dwarf to exceed the Chandrasekhar mass and explode as a Type Ia supernova. It can accrete gas from a donor star, or two white dwarfs can collide. Most astronomers favor the first scenario as the more likely explanation. But we would expect to see certain signs if the theory is correct, and we don't for most Type Ia supernovae.

For example, we should detect small amounts of hydrogen and helium gas near the explosion, but we don't. That gas would come from matter that wasn't accreted by the white dwarf, or from the disruption of the companion star in the explosion. Astronomers also have looked for the donor star after the supernova faded from sight, without success.

Di Stefano and her colleagues suggest that white dwarf spin might solve this puzzle. A spin-up/spin-down process would introduce a long delay between the time of accretion and the explosion. As a white dwarf gains mass, it also gains angular momentum, which speeds up its spin. If the white dwarf rotates fast enough, its spin can help support it, allowing it to cross the 1.4-solar-mass barrier and become a super-Chandrasekhar-mass star.

Once accretion stops, the white dwarf will gradually slow down. Eventually, the spin isn't enough to counteract gravity, leading to a Type Ia supernova.

"Our work is new because we show that spin-up and spin-down of the white dwarf have important consequences. Astronomers therefore must take angular momentum of accreting white dwarfs seriously, even though it's very difficult science," explained Di Stefano.

The spin-down process could produce a time delay of up to a billion years between the end of accretion and the supernova explosion. This would allow the companion star to age and evolve into a second white dwarf, and any surrounding material to dissipate.

In our Galaxy, scientists estimate that there are three Type Ia supernovae every thousand years. If a typical super-Chandrasekhar-mass white dwarf takes millions of years to spin down and explode, then calculations suggest that there should be dozens of pre-explosion systems within a few thousand light-years of Earth.

Those supernova precursors will be difficult to detect. However, upcoming wide-field surveys conducted at facilities like Pan-STARRS and the Large Synoptic Survey Telescope should be able to spot them.

"We don't know of any super-Chandrasekhar-mass white dwarfs in the Milky Way yet, but we're looking forward to hunting them out," said co-author Rasmus Voss of Radboud University Nijmegen, The Netherlands.

VISTA Finds 96 Star Clusters Hidden Behind Dust

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Using data from the VISTA infrared survey telescope at ESO’s Paranal Observatory, an international team of astronomers has discovered 96 new open star clusters hidden by the dust in the Milky Way. These tiny and faint objects were invisible to previous surveys, but they could not escape the sensitive infrared detectors of the world’s largest survey telescope, which can peer through the dust. This is the first time so many faint and small clusters have been found at once.

This result comes just one year after the start of the VISTA Variables in the Via Lactea programme (VVV) [1], one of the six public surveys on the new telescope. The results will appear in the journal Astronomy & Astrophysics.

“This discovery highlights the potential of VISTA and the VVV survey for finding star clusters, especially those hiding in dusty star-forming regions in the Milky Way’s disc. VVV goes much deeper than other surveys,” says Jura Borissova, lead author of the study.

The majority of stars with more than half of the mass of our Sun form in groups, called open clusters. These clusters are the building blocks of galaxies and vital for the formation and evolution of galaxies such as our own. However, stellar clusters form in very dusty regions that diffuse and absorb most of the visible light that the young stars emit, making them invisible to most sky surveys, but not to the 4.1-m infrared VISTA telescope.

“In order to trace the youngest star cluster formation we concentrated our search towards known star-forming areas. In regions that looked empty in previous visible-light surveys, the sensitive VISTA infrared detectors uncovered many new objects,” adds Dante Minniti, lead scientist of the VVV survey.

By using carefully tuned computer software, the team was able to remove the foreground stars appearing in front of each cluster in order to count the genuine cluster members. Afterwards, they made visual inspections of the images to measure the cluster sizes, and for the more populous clusters they made other measurements such as distance, age, and the amount of reddening of their starlight caused by interstellar dust between them and us.

“We found that most of the clusters are very small and only have about 10–20 stars. Compared to typical open clusters, these are very faint and compact objects — the dust in front of these clusters makes them appear 10 000 to 100 million times fainter in visible light. It’s no wonder they were hidden,” explains Radostin Kurtev, another member of the team.

Since antiquity only 2500 open clusters have been found in the Milky Way, but astronomers estimate there might be as many as 30 000 still hiding behind the dust and gas. While bright and large open clusters are easily spotted, this is the first time that so many faint and small clusters have been found at once.

Furthermore, these new 96 open clusters could be only the tip of the iceberg. “We’ve just started to use more sophisticated automatic software to search for less concentrated and older clusters. I am confident that many more are coming soon,” adds Borissova.

Astronomers Find Largest, Most Distant Reservoir of Water

Two teams of astronomers have discovered the largest and farthest reservoir of water ever detected in the universe. The water, equivalent to 140 trillion times all the water in the world's ocean, surrounds a huge, feeding black hole, called a quasar, more than 12 billion light-years away.

"The environment around this quasar is very unique in that it's producing this huge mass of water," said Matt Bradford, a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It's another demonstration that water is pervasive throughout the universe, even at the very earliest times." Bradford leads one of the teams that made the discovery. His team's research is partially funded by NASA and appears in the Astrophysical Journal Letters.

A quasar is powered by an enormous black hole that steadily consumes a surrounding disk of gas and dust. As it eats, the quasar spews out huge amounts of energy. Both groups of astronomers studied a particular quasar called APM 08279+5255, which harbors a black hole 20 billion times more massive than the sun and produces as much energy as a thousand trillion suns.

Astronomers expected water vapor to be present even in the early, distant universe, but had not detected it this far away before. There's water vapor in the Milky Way, although the total amount is 4,000 times less than in the quasar, because most of the Milky Way’s water is frozen in ice.

Water vapor is an important trace gas that reveals the nature of the quasar. In this particular quasar, the water vapor is distributed around the black hole in a gaseous region spanning hundreds of light-years in size (a light-year is about six trillion miles). Its presence indicates that the quasar is bathing the gas in X-rays and infrared radiation, and that the gas is unusually warm and dense by astronomical standards. Although the gas is at a chilly minus 63 degrees Fahrenheit (minus 53 degrees Celsius) and is 300 trillion times less dense than Earth's atmosphere, it's still five times hotter and 10 to 100 times denser than what's typical in galaxies like the Milky Way.

Measurements of the water vapor and of other molecules, such as carbon monoxide, suggest there is enough gas to feed the black hole until it grows to about six times its size. Whether this will happen is not clear, the astronomers say, since some of the gas may end up condensing into stars or might be ejected from the quasar.

Bradford's team made their observations starting in 2008, using an instrument called "Z-Spec" at the California Institute of Technology’s Submillimeter Observatory, a 33-foot (10-meter) telescope near the summit of Mauna Kea in Hawaii. Follow-up observations were made with the Combined Array for Research in Millimeter-Wave Astronomy (CARMA), an array of radio dishes in the Inyo Mountains of Southern California.

The second group, led by Dariusz Lis, senior research associate in physics at Caltech and deputy director of the Caltech Submillimeter Observatory, used the Plateau de Bure Interferometer in the French Alps to find water. In 2010, Lis's team serendipitously detected water in APM 8279+5255, observing one spectral signature. Bradford's team was able to get more information about the water, including its enormous mass, because they detected several spectral signatures of the water

Most Distant Quasar Found

A team of European astronomers has used ESO’s Very Large Telescope and a host of other telescopes to discover and study the most distant quasar found to date. This brilliant beacon, powered by a black hole with a mass two billion times that of the Sun, is by far the brightest object yet discovered in the early Universe. The results will appear in the 30 June 2011 issue of the journal Nature.

“This quasar is a vital probe of the early Universe. It is a very rare object that will help us to understand how supermassive black holes grew a few hundred million years after the Big Bang,” says Stephen Warren, the study’s team leader.

Quasars are very bright, distant galaxies that are believed to be powered by supermassive black holes at their centres. Their brilliance makes them powerful beacons that may help to probe the era when the first stars and galaxies were forming. The newly discovered quasar is so far away that its light probes the last part of the reionisation era [1].

The quasar that has just been found, named ULAS J1120+0641 [2], is seen as it was only 770 million years after the Big Bang (redshift 7.1, [3]). It took 12.9 billion years for its light to reach us.

Although more distant objects have been confirmed (such as a gamma-ray burst at redshift 8.2, eso0917, and a galaxy at redshift 8.6, eso1041), the newly discovered quasar is hundreds of times brighter than these. Amongst objects bright enough to be studied in detail, this is the most distant by a large margin.

The next most-distant quasar is seen as it was 870 million years after the Big Bang (redshift 6.4). Similar objects further away cannot be found in visible-light surveys because their light, stretched by the expansion of the Universe, falls mostly in the infrared part of the spectrum by the time it gets to Earth. The European UKIRT Infrared Deep Sky Survey (UKIDSS) which uses the UK's dedicated infrared telescope [4] in Hawaii was designed to solve this problem. The team of astronomers hunted through millions of objects in the UKIDSS database to find those that could be the long-sought distant quasars, and eventually struck gold.

“It took us five years to find this object,” explains Bram Venemans, one of the authors of the study. “We were looking for a quasar with redshift higher than 6.5. Finding one that is this far away, at a redshift higher than 7, was an exciting surprise. By peering deep into the reionisation era, this quasar provides a unique opportunity to explore a 100-million-year window in the history of the cosmos that was previously out of reach.”

The distance to the quasar was determined from observations made with the FORS2 instrument on ESO’s Very Large Telescope (VLT) and instruments on the Gemini North Telescope [5]. Because the object is comparatively bright it is possible to take a spectrum of it (which involves splitting the light from the object into its component colours). This technique allowed the astronomers to find out quite a lot about the quasar.

These observations showed that the mass of the black hole at the centre of ULAS J1120+0641 is about two billion times that of the Sun. This very high mass is hard to explain so early on after the Big Bang. Current theories for the growth of supermassive black holes predict a slow build-up in mass as the compact object pulls in matter from its surroundings.

“We think there are only about 100 bright quasars with redshift higher than 7 over the whole sky,” concludes Daniel Mortlock, the leading author of the paper. “Finding this object required a painstaking search, but it was worth the effort to be able to unravel some of the mysteries of the early Universe.”
Notes

[1] About 300 000 years after the Big Bang, which occurred 13.7 billion years ago, the Universe had cooled down enough to allow electrons and protons to combine into neutral hydrogen (a gas without electric charge). This cool dark gas permeated the Universe until the first stars started forming about 100 to 150 million years later. Their intense ultraviolet radiation slowly split the hydrogen atoms back into protons and electrons, a process called reionisation, making the Universe more transparent to ultraviolet light. It is believe that this era occurred between about 150 million to 800 million years after the Big Bang.

[2] The object was found using data from the UKIDSS Large Area Survey, or ULAS. The numbers and prefix ‘J’ refer to the quasar’s position in the sky.

[3] Because light travels at a finite speed, astronomers look back in time as they look further away into the Universe. It took 12.9 billion years for the light from ULAS J1120+0641 to travel to telescopes on Earth so the quasar is seen as it was when the Universe was only 770 million years old. In those 12.9 billion years, the Universe expanded and the light from the object stretched as a result. The cosmological redshift, or simply redshift, is a measure of the total stretching the Universe underwent between the moment when the light was emitted and the time when it was received.

[4] UKIRT is the United Kingdom Infrared Telescope. It is owned by the UK’s Science and Technology Facilities Council and operated by the staff of the Joint Astronomy Centre in Hilo, Hawaii.

[5] FORS2 is the VLT’s FOcal Reducer and low dispersion Spectrograph. Other instruments used to split up the light of the object were the Gemini Multi-Object Spectrograph (GMOS) and the Gemini Near-Infrared Spectrograph (GNIRS). The Liverpool Telescope, the Isaac Newton Telescope and the UK Infrared Telescope (UKIRT) were also used to confirm survey measurements.

NASA Telescope Helps Confirm Nature of Dark Energy

A five-year survey of 200,000 galaxies, stretching back seven billion years in cosmic time, has led to one of the best independent confirmations that dark energy is driving our universe apart at accelerating speeds. The survey used data from NASA's space-based Galaxy Evolution Explorer and the Anglo-Australian Telescope on Siding Spring Mountain in Australia.

The findings offer new support for the favored theory of how dark energy works -- as a constant force, uniformly affecting the universe and propelling its runaway expansion. They contradict an alternate theory, where gravity, not dark energy, is the force pushing space apart. According to this alternate theory, with which the new survey results are not consistent, Albert Einstein's concept of gravity is wrong, and gravity becomes repulsive instead of attractive when acting at great distances.

"The action of dark energy is as if you threw a ball up in the air, and it kept speeding upward into the sky faster and faster," said Chris Blake of the Swinburne University of Technology in Melbourne, Australia. Blake is lead author of two papers describing the results that appeared in recent issues of the Monthly Notices of the Royal Astronomical Society. "The results tell us that dark energy is a cosmological constant, as Einstein proposed. If gravity were the culprit, then we wouldn't be seeing these constant effects of dark energy throughout time."

Dark energy is thought to dominate our universe, making up about 74 percent of it. Dark matter, a slightly less mysterious substance, accounts for 22 percent. So-called normal matter, anything with atoms, or the stuff that makes up living creatures, planets and stars, is only approximately four percent of the cosmos.

The idea of dark energy was proposed during the previous decade, based on studies of distant exploding stars called supernovae. Supernovae emit constant, measurable light, making them so-called "standard candles," which allows calculation of their distance from Earth. Observations revealed dark energy was flinging the objects out at accelerating speeds.

Dark energy is in a tug-of-war contest with gravity. In the early universe, gravity took the lead, dominating dark energy. At about 8 billion years after the Big Bang, as space expanded and matter became diluted, gravitational attractions weakened and dark energy gained the upper hand. Billions of years from now, dark energy will be even more dominant. Astronomers predict our universe will be a cosmic wasteland, with galaxies spread apart so far that any intelligent beings living inside them wouldn't be able to see other galaxies.

The new survey provides two separate methods for independently checking the supernovae results. This is the first time astronomers performed these checks across the whole cosmic timespan dominated by dark energy. The team began by assembling the largest three-dimensional map of galaxies in the distant universe, spotted by the Galaxy Evolution Explorer. The ultraviolet-sensing telescope has scanned about three-quarters of the sky, observing hundreds of millions of galaxies.

"The Galaxy Evolution Explorer helped identify bright, young galaxies, which are ideal for this type of study," said Christopher Martin, principal investigator for the mission at the California Institute of Technology in Pasadena. "It provided the scaffolding for this enormous 3-D map."

The astronomers acquired detailed information about the light for each galaxy using the Anglo-Australian Telescope and studied the pattern of distance between them. Sound waves from the very early universe left imprints in the patterns of galaxies, causing pairs of galaxies to be separated by approximately 500 million light-years.

This "standard ruler" was used to determine the distance from the galaxy pairs to Earth -- the closer a galaxy pair is to us, the farther apart the galaxies will appear from each other on the sky. As with the supernovae studies, this distance data were combined with information about the speeds at which the pairs are moving away from us, revealing, yet again, the fabric of space is stretching apart faster and faster.

The team also used the galaxy map to study how clusters of galaxies grow over time like cities, eventually containing many thousands of galaxies. The clusters attract new galaxies through gravity, but dark energy tugs the clusters apart. It slows down the process, allowing scientists to measure dark energy's repulsive force.

"Observations by astronomers over the last 15 years have produced one of the most startling discoveries in physical science; the expansion of the universe, triggered by the Big Bang, is speeding up," said Jon Morse, astrophysics division director at NASA Headquarters in Washington. "Using entirely independent methods, data from the Galaxy Evolution Explorer have helped increase our confidence in the existence of dark energy."

Close-up of the drama of star formation

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This very detailed enhanced-colour image from ESO’s Very Large Telescope shows the dramatic effects of very young stars on the dust and gas from which they were born in the star-forming region NGC 6729. The baby stars are invisible in this picture, being hidden behind dust clouds at the upper left of the picture, but material they are ejecting is crashing into the surroundings at speeds of that can be as high as one million kilometres per hour. This picture was taken by the FORS1 instrument and records the scene in the light of glowing hydrogen and sulphur.

T Pyxidis Finally Blows Again

T Pyx on April 15, 2011

The recurrent nova T Pyxidis, which had its last outburst in December 1966 and has been very overdue for its next, has shot up from magnitude 15.4 to at least 8.5. In 1966–67 it reached 6.5.

It's in the dim constellation Pyxis east of Puppis and Canis Major. Pyxis is currently fairly high in the south-southwest right after dark, in good view for observers at north temperate latitudes and points south. The star is at declination –32°.

Here are finder and comparison-star charts from Sky & Telescope, and larger-scale comparison-star charts 15° wide, 5° wide, and
2° wide courtesy of the American Association of Variable Star Observers (AAVSO). On all charts north is up and east is to the left. The numbers next to stars are comparison-star magnitudes to the nearest tenth with the decimal points omitted.

A Very Cool Pair of Brown Dwarfs

Brown dwarfs are essentially failed stars: they lack enough mass for gravity to trigger the nuclear reactions that make stars shine. The newly discovered brown dwarf, identified as CFBDSIR 1458+10B, is the dimmer member of a binary brown dwarf system located just 75 light-years from Earth [1].

The powerful X-shooter spectrograph on ESO’s Very Large Telescope (VLT) was used to show that the composite object was very cool by brown dwarf standards. "We were very excited to see that this object had such a low temperature, but we couldn’t have guessed that it would turn out to be a double system and have an even more interesting, even colder component," said Philippe Delorme of the Institut de planétologie et d’astrophysique de Grenoble (CNRS/Université Joseph Fourier), a co-author of the paper. CFBDSIR 1458+10 is the coolest brown dwarf binary found to date.

The dimmer of the two dwarfs has now been found to have a temperature of about 100 degrees Celsius — the boiling point of water, and not much different from the temperature inside a sauna [2]. “At such temperatures we expect the brown dwarf to have properties that are different from previously known brown dwarfs and much closer to those of giant exoplanets — it could even have water clouds in its atmosphere," said Michael Liu of the University of Hawaii’s Institute for Astronomy, who is lead author of the paper describing this new work. "In fact, once we start taking images of gas-giant planets around Sun-like stars in the near future, I expect that many of them will look like CFBDSIR 1458+10B."

Unravelling the secrets of this unique object involved exploiting the power of three different telescopes. CFBDSIR 1458+10 was first found to be a binary using the Laser Guide Star (LGS) Adaptive Optics system on the Keck II Telescope in Hawaii [3]. Liu and his colleagues then employed the Canada–France–Hawaii Telescope, also in Hawaii, to determine the distance to the brown dwarf duo using an infrared camera [4]. Finally the ESO VLT was used to study the object’s infrared spectrum and measure its temperature.

The hunt for cool objects is a very active astronomical hot topic. The Spitzer Space Telescope has recently identified two other very faint objects as other possible contenders for the coolest known brown dwarfs, although their temperatures have not been measured so precisely. Future observations will better determine how these objects compare to CFBDSIR 1458+10B. Liu and his colleagues are planning to observe CFBDSIR 1458+10B again to better determine its properties and to begin mapping the binary's orbit, which, after about a decade of monitoring, should allow astronomers to determine the binary’s mass.

The Drama of Starbirth

The star-forming region NGC 6729 is part of one of the closest stellar nurseries to the Earth and hence one of the best studied. This new image from ESO’s Very Large Telescope gives a close-up view of a section of this strange and fascinating region (a wide-field view is available here: eso1027). The data were selected from the ESO archive by Sergey Stepanenko as part of the Hidden Treasures competition [1]. Sergey’s picture of NGC 6729 was ranked third in the competition.

Stars form deep within molecular clouds and the earliest stages of their development cannot be seen in visible-light telescopes because of obscuration by dust. In this image there are very young stars at the upper left of the picture. Although they cannot be seen directly, the havoc that they have wreaked on their surroundings dominates the picture. High-speed jets of material that travel away from the baby stars at velocities as high as one million kilometres per hour are slamming into the surrounding gas and creating shock waves. These shocks cause the gas to shine and create the strangely coloured glowing arcs and blobs known as Herbig–Haro objects [2].

In this view the Herbig–Haro objects form two lines marking out the probable directions of ejected material. One stretches from the upper left to the lower centre, ending in the bright, circular group of glowing blobs and arcs at the lower centre. The other starts near the left upper edge of the picture and extends towards the centre right. The peculiar scimitar-shaped bright feature at the upper left is probably mostly due to starlight being reflected from dust and is not a Herbig–Haro object.

This enhanced-colour picture [3] was created from images taken using the FORS1 instrument on ESO’s Very Large Telescope. Images were taken through two different filters that isolate the light coming from glowing hydrogen (shown as orange) and glowing ionised sulphur (shown as blue). The different colours in different parts of this violent star formation region reflect different conditions — for example where ionised sulphur is glowing brightly (blue features) the velocities of the colliding material are relatively low — and help astronomers to unravel what is going on in this dramatic scene.

QUASAR’S BELCH SOLVES LONGSTANDING MYSTERY

For the first time, observations with the Gemini Observatory clearly reveal an extreme, large-scale galactic outflow that brings the cosmic dinner to a halt. The outflow is effectively blowing the galaxy apart in a negative feedback loop, depriving the galaxy’s monstrous black hole of the gas and dust it needs to sustain its frenetic growth. It also limits the material available for the galaxy to make new generations of stars.

The groundbreaking work is a collaboration between David Rupke of Rhodes College in Tennessee and the University of Maryland’s Sylvain Veilleux. The results are to be published in the March 10 issue of The Astrophysical Journal Letters and were completed with support from the U.S. National Science Foundation.

According to Veilleux, Markarian 231 (Mrk 231), the galaxy observed with Gemini, is an ideal laboratory for studying outflows caused by feedback from supermassive black holes. “This object is arguably the closest and best example that we know of a big galaxy in the final stages of a violent merger and in the process of shedding its cocoon and revealing a very energetic central quasar. This is really a last gasp of this galaxy; the black hole is belching its next meals into oblivion!” As extreme as Mrk 231’s eating habits appear, Veilleux adds that they are probably not unique, “When we look deep into space and back in time, quasars like this one are seen in large numbers and all of them may have gone through shedding events like the one we are witnessing in Mrk 231.”

Although Mrk 231 is extremely well studied, and known for its collimated jets, the Gemini observations exposed a broad outflow extending in all directions for at least 8,000 light years around the galaxy’s core. The resulting data reveal gas (characterized by sodium, which absorbs yellow light) streaming away from the galaxy center at speeds of over 1,000 kilometers per second. At this speed, the gas could go from New York to Los Angeles in about 4 seconds. This outflow is removing gas from the nucleus at a prodigious rate – more than 2.5 times the star formation rate. The speeds observed eliminate stars as the possible “engine” fueling the outflow. This leaves the black hole itself as the most likely culprit, and it can easily account for the tremendous energy required.

The energy involved is sufficient to sweep away matter from the galaxy. However, "when we say the galaxy is being blown apart, we are only referring to the gas and dust in the galaxy,” notes Rupke. “The galaxy is mostly stars at this stage in its life, and the outflow has no effect on them. The crucial thing is that the fireworks of new star formation and black hole feeding are coming to an end, most likely as a result of this outflow.”

The environment around such a black hole is commonly known as an active galactic nucleus (AGN), and the extreme influx of material into these black holes is the power source for quasi-stellar objects or quasars. Merging galaxies help to feed the central black hole and also shroud it in gas. Mrk 231 is in transition, now clearing its surroundings. Eventually, running out of fuel, the AGN will become extinct. Without gas to form new stars, the host galaxy also starves to death, turning into a collection of old aging stars with few young stars to regenerate the stellar population. Ultimately, these old stars will make the galaxy appear redder giving these galaxies the moniker “red and dead.”

Numerical astrophysicist Philip Hopkins, a Miller Fellow at the University of California at Berkeley, explains that many physical processes unique to rapidly growing black holes are likely to play a role in propelling the winds observed by Gemini. “At its peak, the quasar shines with such intensity that the light itself is ‘trapped’ by a cocoon of gas and dust pushing on material with a force that can easily overcome the gravitational pull of the black hole.” Hopkins adds that the bath of X-rays and gamma rays known to be generated by quasars could also heat up the gas in the galaxy’s center until it reaches a temperature where it "boils over" and causes a bomb-like explosion. “But until now, we haven’t been able to catch a system ‘in the act.’” Part of the problem, according to Hopkins, has been that the most visible outflows are those ‘collimated jets’ already known in Mrk 231. These jets are trapped (probably by magnetic fields) in an extremely narrow beam, whereas material is falling into the black hole from all directions. The previously known jets therefore only cause very localized damage – drilling a tiny hole in the cocoon, rather than sweeping it away more broadly as seen in these new, more all-encompassing, outflows.

The observations for this study were obtained with the Gemini Multi-Object Spectrograph (GMOS) on Gemini North, on Mauna Kea, Hawai‘i. The study used a powerful technique known as integral field spectroscopy. The integral field unit (IFU) in GMOS obtains a spectrum at several hundred points around the galaxy’s core. Each spectrum is then, in turn, used to determine the velocity of the gas at that point and represents the third dimension in what is called a data cube.

Markarian 231 is located about 600 million light years away in the direction of the constellation of Ursa Major. Although its mass is uncertain, some estimates indicate that Mrk 231 has a mass in stars about three times that of our Milky Way galaxy and its central black hole is estimated to have a mass of at least ten million solar masses or also about three times that of the supermassive black hole in the Milky Way.

Reflected Glory

The nebula Messier 78 takes centre stage in this image taken with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile, while the stars powering the bright display take a backseat. The brilliant starlight ricochets off dust particles in the nebula, illuminating it with scattered blue light. Igor Chekalin was the overall winner of ESO’s Hidden Treasures 2010 astrophotography competition with his image of this stunning object.

Messier 78 is a fine example of a reflection nebula. The ultraviolet radiation from the stars that illuminate it is not intense enough to ionise the gas to make it glow — its dust particles simply reflect the starlight that falls on them. Despite this, Messier 78 can easily be observed with a small telescope, being one of the brightest reflection nebulae in the sky. It lies about 1350 light-years away in the constellation of Orion (The Hunter) and can be found northeast of the easternmost star of Orion’s belt.

This new image of Messier 78 from the MPG/ESO 2.2-metre telescope at the La Silla Observatory is based on data selected by Igor Chekalin in his winning entry to the Hidden Treasures competition [1].

The pale blue tint seen in the nebula in this picture is an accurate representation of its dominant colour. Blue hues are commonly seen in reflection nebulae because of the way the starlight is scattered by the tiny dust particles that they contain: the shorter wavelength of blue light is scattered more efficiently than the longer wavelength red light.

This image contains many other striking features apart from the glowing nebula. A thick band of obscuring dust stretches across the image from the upper left to the lower right, blocking the light from background stars. In the bottom right corner, many curious pink structures are also visible, which are created by jets of material being ejected from stars that have recently formed and are still buried deep in dust clouds.

Two bright stars, HD 38563A and HD 38563B, are the main powerhouses behind Messier 78. However, the nebula is home to many more stars, including a collection of about 45 low mass, young stars (less than 10 million years old) in which the cores are still too cool for hydrogen fusion to start, known as T Tauri stars. Studying T Tauri stars is important for understanding the early stages of star formation and how planetary systems are created.

Remarkably, this complex of nebulae has also changed significantly in the last ten years. In February 2004 the experienced amateur observer Jay McNeil took an image of this region with a 75 mm telescope and was surprised to see a bright nebula — the prominent fan shaped feature near the bottom of this picture — where nothing was seen on most earlier images. This object is now known as McNeil’s Nebula and it appears to be a highly variable reflection nebula around a young star.

This colour picture was created from many monochrome exposures taken through blue, yellow/green and red filters, supplemented by exposures through an H-alpha filter that shows light from glowing hydrogen gas. The total exposure times were 9, 9, 17.5 and 15.5 minutes per filter, respectively.
Notes

[1] Igor Chekalin from Russia uncovered the raw data for this image of Messier 78 in ESO’s archives in the competition Hidden Treasures (eso1102). He processed the raw data with great skill, claiming first prize in the contest for his final image (Flickr link). ESO’s team of in-house image processing experts then independently processed the raw data at full resolution to produce the image shown here.

Get Ready for a Solar-System Bonanza

Don't get me wrong: I would never suggest that NASA throttle back its efforts to explore the worlds around us. But I have to admit that, even for folks like me who follow space activities closely, things are getting a little crazy. Over the next several months, interplanetary exploration will rev up to a dizzying pace.

The first event occurred just a few days ago, when the twin STEREO spacecraft finally took up positions on opposite sides of the Sun. (We space junkies sometimes forget that the Sun is part of our solar system.) For the first time, solar scientists can monitor all of the Sun's disk at once — and that'll pay big dividends as solar activity ramps up in the months ahead.

An artist's portrayal of the Stardust spacecraft approaching Comet Tempel 1 on February 14, 2011.

Coming up fast is a return visit to Comet 9P/Tempel 1. You'll recall that this 5-by-3-mile iceberg was the target of NASA's Deep Impact mission on July 4, 2005. When a 815-pound (370-kg) projectile slammed into the comet's nucleus, it unleashed an unexpected fireworks display of gas and dust.

Since then Tempel 1 has made one complete trip around the Sun, and on February 14th it'll again be in the crosshairs (this time just with instruments) of the Stardust
spacecraft. This is a great example of how old spacecraft can do new tricks: Stardust completed its primary mission five years ago after zipping through the coma of Comet Wild 2 in early 2004 and dropping off a sample capsule when it swung past Earth. But the main spacecraft remained in solar orbit, and now it's posed to reconnoiter a second
comet.

(Officially, the mission's name is now Stardust-NeXT — that latter bit standing for "New Exploration of Tempel 1" — but it's just too much of a stretch for my taste.)

In the best of all worlds, Stardust's camera would record the crater made by Deep Impact's copper-cored cannonball. But even if the nucleus has rotated it from view, there's still plenty to look at. The nucleus of Tempel 1 appears to have multiple layers and bizarre flows. Can a mountain-size blob of ice and dirt be geologically active? We'll have more answers to that question very soon.

There's no letup in the pace of solar-system exploration once Stardust has its hi-and-bye. In fact, NASA officials
have dubbed 2011 the "Year of the Solar System." Well, truth be told, in their minds YSS began last October, when Deep Impact visited its second comet, 103P/Hartley 2, and it won't end until August 2012, when the not-even-launched-yet rover Curiosity (a.k.a. Mars Science Laboratory) reaches Mars.

Whatever. Here's a rundown of the other interplanetary headlines you can expect to see in the coming months:

March 18: After three warm-up flybys, NASA's Messenger
spacecraft will fire its braking rocket and slip into a looping polar
orbit around Mercury that comes within 125 miles (200 km) of its
surface. Equipped with seven very capable cameras, spectrometers, and
other instruments, Messenger has already made a trove of new
discoveries about the innermost planet. But the real science
breakthroughs (such as its interior structure) will come after the
orbiter has made long-term observations. Messenger is a contraction of
"Mercury Surface, Space Environment, Geochemistry, and Ranging."

July 16:
The Dawn spacecraft will reach 4 Vesta, which is hands down the
asteroid belt's most amazing chunk of rock: it's thought to have an
iron–nickel core, a rocky olivine mantle, a crust, lava flows, and a
giant crater. The spacecraft has been almost gliding toward Vesta using
ion-fueled thrusters, and it will remain in orbit for a year before
easing away and setting course for 1 Ceres. (Remarkably, Dawn isn't an
acronym and doesn't stand for anything.) This mission's website is here, and I highly recommend the "Dawn Journal" written by chief engineer Marc Rayman.

August 5: The launch date for NASA's ambitious Juno
spacecraft. This is the first outer-planet-bound spacecraft to use
solar-cell arrays, rather than plutonium power packs, to generate
electricity. When it reaches Jupiter in 2016, Juno is to slip into a
looping polar orbit that will both subject it to dangerously high
radiation levels and, its science team hopes, answer key questions
about the planet's composition, its interior structure, and from those
how our solar system formed. Also not an acronym, Juno is named for the
jealous god-sister-wife of Jupiter in Roman mythology.

September 8: Lunar scientists will look on expectantly as the twin GRAIL
spacecraft rocket skyward from Cape Canaveral, Florida. The Gravity
Recovery and Interior Laboratory mission intends to fly these craft in
tandem just 30 miles (50 km) above the lunar surface. By carefully
tracking how the Moon's gravity alters the crafts' orbital motion,
scientists hope to map the Moon's gravity field with unprecedented
detail and, using that, derive the detailed structure of the lunar
interior from crust to core.

November 8: If everything comes together in time, the Russian Space Agency plans to launch its problematic Phobos-Grunt mission. (Grunt is Russian for "ground".) Talk about a checkered history!
Conceived in 1996 to land on the larger of Mars's two satellites and
return a sample to Earth, this spacecraft has had more transformations
than Cher at the Academy Awards! In its latest configuration, the
spacecraft will carry a passenger, the Chinese-built spacecraft Yinghou
1, which will detach from Phobos-Grunt and orbit Mars for up to a year.
Plans still call for the main spacecraft to land on Phobos, scoop up
several samples totaling a total of 3 to 5½ ounces (85 to 160 g), and
return them to Earth by early 2013.

November 25: Another troubled mission, Mars Science Laboratory,
will begin its flight to Mars. The primary scientific objective is
straightforward: assess whether the Red Planet ever had an environment
conducive to life — or still does. But MSL, renamed Curiosity after a Disney-inspired contest in 2009, has had a world of trouble getting to the launch pad. The beefy 1-ton lander should have already reached Mars, but development problems caused a two-year launch delay and ballooned its price tag to $2½ billion.

All these dates are subject to change, so to keep up to date I recommend that you check Ron Baalke's comprehensive Space Calendar for the latest schedules.

Earth-Size Planet Candidates Found in Habitable Zone

PASADENA, Calif. -- NASA's Kepler mission has discovered its first Earth-size planet candidates and its first candidates in the habitable zone, a region where liquid water could exist on a planet's surface. Five of the potential planets are near Earth-size and orbit in the habitable zone of smaller, cooler stars than our sun.

Candidates require follow-up observations to verify they are actual planets. Kepler also found six confirmed planets orbiting a sun-like star, Kepler-11. This is the largest group of transiting planets orbiting a single star yet discovered outside our solar system.

"In one generation we have gone from extraterrestrial planets being a mainstay of science fiction, to the present, where Kepler has helped turn science fiction into today's reality," said NASA Administrator Charles Bolden. "These discoveries underscore the importance of NASA's science missions, which consistently increase understanding of our place in the cosmos."

The discoveries are part of several hundred new planet candidates identified in new Kepler mission science data, released on Tuesday, Feb. 1. The findings increase the number of planet candidates identified by Kepler to-date to 1,235. Of these, 68 are approximately Earth-size; 288 are super-Earth-size; 662 are Neptune-size; 165 are the size of Jupiter and 19 are larger than Jupiter. Of the 54 new planet candidates found in the habitable zone, five are near Earth-sized. The remaining 49 habitable zone candidates range from super-Earth size -- up to twice the size of Earth -- to larger than Jupiter.

The findings are based on the results of observations conducted May 12 to Sept. 17, 2009, of more than 156,000 stars in Kepler's field of view, which covers approximately one four-hundredth of the sky.

"The fact that we've found so many planet candidates in such a tiny fraction of the sky suggests there are countless planets orbiting sun-like stars in our galaxy," said William Borucki of NASA's Ames Research Center in Moffett Field, Calif., the mission's science principal investigator. "We went from zero to 68 Earth-sized planet candidates and zero to 54 candidates in the habitable zone, some of which could have moons with liquid water."

Among the stars with planetary candidates, 170 show evidence of multiple planetary candidates. Kepler-11, located approximately 2,000 light years from Earth, is the most tightly packed planetary system yet discovered. All six of its confirmed planets have orbits smaller than Venus, and five of the six have orbits smaller than Mercury's. The only other star with more than one confirmed transiting planet is Kepler-9, which has three. The Kepler-11 findings will be published in the Feb. 3 issue of the journal Nature.

"Kepler-11 is a remarkable system whose architecture and dynamics provide clues about its formation," said Jack Lissauer, a planetary scientist and Kepler science team member at Ames. "These six planets are mixtures of rock and gases, possibly including water. The rocky material accounts for most of the planets' mass, while the gas takes up most of their volume. By measuring the sizes and masses of the five inner planets, we determined they are among the lowest-mass confirmed planets beyond our solar system."

All of the planets orbiting Kepler-11 are larger than Earth, with the largest ones being comparable in size to Uranus and Neptune. The innermost planet, Kepler-11b, is 10 times closer to its star than Earth is to the sun. Moving outward, the other planets are Kepler-11c, Kepler-11d, Kepler-11e, Kepler-11f, and the outermost planet, Kepler-11g, which is half as far from its star as Earth is from the sun.

The planets Kepler-11d, Kepler-11e and Kepler-11f have a significant amount of light gas, which indicates that they formed within a few million years of the system's formation.

"The historic milestones Kepler makes with each new discovery will determine the course of every exoplanet mission to follow," said Douglas Hudgins, Kepler program scientist at NASA Headquarters in Washington.

Kepler, a space telescope, looks for planet signatures by measuring tiny decreases in the brightness of stars caused by planets crossing in front of them. This is known as a transit. Since transits of planets in the habitable zone of sun-like stars occur about once a year and require three transits for verification, it is expected to take three years to locate and verify Earth-size planets orbiting sun-like stars.

The Kepler science team uses ground-based telescopes and NASA's Spitzer Space Telescope to review observations on planetary candidates and other objects of interest the spacecraft finds. The star field that Kepler observes in the constellations Cygnus and Lyra can only be seen from ground-based observatories in spring through early fall. The data from these other observations help determine which candidates can be validated as planets.

Ames manages Kepler's ground system development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., managed Kepler mission development. Ball Aerospace & Technologies Corp. in Boulder, Colo., developed the Kepler flight system and supports mission operations with the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. The Space Telescope Science Institute in Baltimore archives, hosts and distributes the Kepler science data. Kepler is NASA's 10th Discovery Mission and is funded by NASA's Science Mission Directorate at the agency's headquarters. JPL is a division of the California Institute of Technology in Pasadena.

Hubble Finds Most Distant Galaxy Candidate Ever Seen in Universe

How far is far? And, when do you know when you get there? This is not a Dr. Seuss riddle, but the ultimate "final frontier" confronting astronomers. We are on the cusp of seeing nearly as far as we ever can into the universe of stars and galaxies. The question can be better phrased: How young is young? And how do you know when you've seen the earliest objects that ever existed? That's because the farther we look into space the further back into time we see. We're accustomed to instantaneous communications on Earth, but starlight carries a roaming fee. It takes billions of years for information to reach us from the remote universe.

Now astronomers have pushed the Hubble Space Telescope to its limits by finding what they believe is the most distant object ever seen in the universe. Its light traveled 13.2 billion years to reach Hubble. The dim object is a compact galaxy of blue stars that existed 480 million years after the Big Bang, only four percent of the universe's current age. It is tiny. Astronomers were surprised to discover that these observations offer evidence that the rate at which the universe was forming stars grew precipitously in about a 200-million-year time span. This huge change in the rate of star birth means that if astronomers can probe a little further back in time they are going to see even more dramatic changes. This will require the power of the James Webb Space Telescope, the planned successor to Hubble, which will be launched later this decade.

Hubble Zooms in on a Space Oddity

A strange, glowing green cloud of gas that has mystified astronomers since its discovery in 2007 has been studied by Hubble. The cloud of gas is lit up by the bright light of a nearby quasar, and shows signs of ongoing star formation.

One of the strangest space objects ever seen is being scrutinised by the penetrating vision of the NASA/ESA Hubble Space Telescope. A mysterious, glowing green blob of gas is floating in space near a spiral galaxy. Hubble uncovered delicate filaments of gas and a pocket of young star clusters in the giant object, which is the size of the Milky Way.

The Hubble revelations are the latest finds in an ongoing probe of Hanny’s Voorwerp (Hanny’s Object in Dutch). It is named after Hanny van Arkel, the Dutch schoolteacher who discovered the ghostly structure in 2007 while participating in the online Galaxy Zoo project. Galaxy Zoo enlists the public to help classify more than a million galaxies catalogued in the Sloan Digital Sky Survey. The project has expanded to include Galaxy Zoo: Hubble, in which the public is asked to assess tens of thousands of galaxies in deep imagery from the Hubble Space Telescope.

In the sharpest view yet of Hanny’s Voorwerp, Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys have uncovered star birth in a region of the green object that faces the spiral galaxy IC 2497, located about 650 million light-years from Earth. Radio observations have shown an outflow of gas arising from the galaxy’s core. The new Hubble images reveal that the galaxy’s gas is interacting with a small region of Hanny’s Voorwerp, which is collapsing and forming stars. The youngest stars are a couple of million years old.

The greenish Voorwerp is visible because a searchlight beam of light from the galaxy’s core has illuminated it. This beam came from a quasar — a bright, energetic object that is powered by a black hole. The quasar is thought to have turned off less than 200 000 years ago.

Astronomer Bill Keel of the University of Alabama in Tuscaloosa, USA, leader of the Hubble study, is presenting his results on this object today at the American Astronomical Society meeting in Seattle, USA. Read more about his preliminary findings in the NASA news release linked below.

Andromeda's once and future stars

During Christmas 2010, ESA's Herschel and XMM-Newton space observatories targeted the nearest large spiral galaxy M31. This is a galaxy similar to our own Milky Way – both contain several hundred billion stars. This is the most detailed far-infrared image of the Andromeda Galaxy ever taken and shows clearly that more stars are on their way.

Sensitive to far-infrared light, Herschel sees clouds of cool dust and gas where stars can form. Inside these clouds are many dusty cocoons containing forming stars, each star pulling itself together in a slow gravitational process that can last for hundreds of millions of years. Once a star reaches a high enough density, it will begin to shine at optical wavelengths. It will emerge from its birth cloud and become visible to ordinary telescopes.

Many galaxies are spiral in shape but Andromeda is interesting because it shows a large ring of dust about 75 000 light-years across encircling the centre of the galaxy. Some astronomers speculate that this dust ring may have been formed in a recent collision with another galaxy. This new Herschel image reveals yet more intricate details, with at least five concentric rings of star-forming dust visible.

Superimposed on the infrared image is an X-ray view taken almost simultaneously by ESA's XMM-Newton observatory. Whereas the infrared shows the beginnings of star formation, X-rays usually show the endpoints of stellar evolution.

XMM-Newton highlights hundreds of X-ray sources within Andromeda, many of them clustered around the centre, where the stars are naturally found to be more crowded together. Some of these are shockwaves and debris rolling through space from exploded stars, others are pairs of stars locked in a gravitational fight to the death.

In these deadly embraces, one star has already died and is pulling gas from its still-living companion. As the gas falls through space, it heats up and gives off X-rays. The living star will eventually be greatly depleted, having much of its mass torn from it by the stronger gravity of its denser partner. As the stellar corpse wraps itself in this stolen gas, it could explode.

Both the infrared and X-ray images show information that is impossible to collect from the ground because these wavelengths are absorbed by Earth's atmosphere. The twinkling starlight seen from Earth is indeed a beautiful sight but in reality contains less than half the story. Visible light shows us the adult stars, whereas infrared gives us the youngsters and X-rays show those in their death throes.

To chart the lives of stars, we need to see it all and that is where Herschel and XMM-Newton contribute so much.

Light Dawns on Dark Gamma-ray Bursts

Gamma-ray bursts are among the most energetic events in the Universe, but some appear curiously faint in visible light. The biggest study to date of these so-called dark gamma-ray bursts, using the GROND instrument on the 2.2-metre MPG/ESO telescope at La Silla in Chile, has found that these gigantic explosions don’t require exotic explanations. Their faintness is now fully explained by a combination of causes, the most important of which is the presence of dust between the Earth and the explosion.

Gamma-ray bursts (GRBs), fleeting events that last from less than a second to several minutes, are detected by orbiting observatories that can pick up their high energy radiation. Thirteen years ago, however, astronomers discovered a longer-lasting stream of less energetic radiation coming from these violent outbursts, which can last for weeks or even years after the initial explosion. Astronomers call this the burst’s afterglow.

While all gamma-ray bursts [1] have afterglows that give off X-rays, only about half of them were found to give off visible light, with the rest remaining mysteriously dark. Some astronomers suspected that these dark afterglows could be examples of a whole new class of gamma-ray bursts, while others thought that they might all be at very great distances. Previous studies had suggested that obscuring dust between the burst and us might also explain why they were so dim.

“Studying afterglows is vital to further our understanding of the objects that become gamma-ray bursts and what they tell us about star formation in the early Universe,” says the study’s lead author Jochen Greiner from the Max-Planck Institute for Extraterrestrial Physics in Garching bei München, Germany.

NASA launched the Swift satellite at the end of 2004. From its orbit above the Earth’s atmosphere it can detect gamma-ray bursts and immediately relay their positions to other observatories so that the afterglows could be studied. In the new study, astronomers combined Swift data with new observations made using GROND [2] — a dedicated gamma-ray burst follow-up observation instrument, which is attached to the 2.2-metre MPG/ESO telescope at La Silla in Chile. In doing so, astronomers have conclusively solved the puzzle of the missing optical afterglow.

What makes GROND exciting for the study of afterglows is its very fast response time — it can observe a burst within minutes of an alert coming from Swift using a special system called the Rapid Response Mode — and its ability to observe simultaneously through seven filters covering both the visible and near-infrared parts of the spectrum.

By combining GROND data taken through these seven filters with Swift observations, astronomers were able to accurately determine the amount of light emitted by the afterglow at widely differing wavelengths, all the way from high energy X-rays to the near-infrared. The astronomers used this information to directly measure the amount of obscuring dust that the light passed through en route to Earth. Previously, astronomers had to rely on rough estimates of the dust content [3].

The team used a range of data, including their own measurements from GROND, in addition to observations made by other large telescopes including the ESO Very Large Telescope, to estimate the distances to nearly all of the bursts in their sample. While they found that a significant proportion of bursts are dimmed to about 60–80 percent of the original intensity by obscuring dust, this effect is exaggerated for the very distant bursts, letting the observer see only 30–50 percent of the light [4]. The astronomers conclude that most dark gamma-ray bursts are therefore simply those that have had their small amount of visible light completely stripped away before it reaches us.

“Compared to many instruments on large telescopes, GROND is a low cost and relatively simple instrument, yet it has been able to conclusively resolve the mystery surrounding dark gamma-ray bursts,” says Greiner.
Notes

[1] Gamma-ray bursts lasting longer than two seconds are referred to as long bursts and those with a shorter duration are known as short bursts. Long bursts, which were observed in this study, are associated with the supernova explosions of massive young stars in star-forming galaxies. Short bursts are not well understood, but are thought to originate from the merger of two compact objects such as neutron stars.

[2] The Gamma-Ray burst Optical and Near-infrared Detector (GROND) was designed and built at the Max-Planck Institute for Extraterrestrial Physics in collaboration with the Tautenburg Observatory, and has been fully operational since August 2007.

[3] Other studies relating to dark gamma-ray bursts have been released. Early this year, astronomers used the Subaru Telescope to observe a single gamma-ray burst, from which they hypothesised that dark gamma-ray bursts may indeed be a separate sub-class that form through a different mechanism, such as the merger of binary stars. In another study published last year using the Keck Telescope, astronomers studied the host galaxies of 14 dark GRBs, and based on the derived low redshifts they infer dust as the likely mechanism to create the dark bursts. In the new work reported here, 39 GRBs were studied, including nearly 20 dark bursts, and it is the only study in which no prior assumptions have been made and the amount of dust has been directly measured.

[4] Because the afterglow light of very distant bursts is redshifted due to the expansion of the Universe, the light that left the object was originally bluer than the light we detect when it gets to Earth. Since the reduction of light intensity by dust is greater for blue and ultraviolet light than for red, this means that the overall dimming effect of dust is greater for the more distant gamma-ray bursts. This is why GROND’s ability to observe near-infrared radiation makes such a difference.