The brightest gamma-ray burst ever seen in X-rays temporarily blinded Swift's X-ray Telescope on 21 June 2010. This image merges the X-rays (red to yellow) with the same view from Swift's Ultraviolet/Optical Telescope, which showed nothing extraordinary. Credit: NASA/Swift/Stefan Immler
[/caption]
A record-breaking gamma ray burst from beyond the Milky Way temporarily blinded the X-ray eye on NASA’s Swift space observatory on June 21, 2010. The X-rays traveled through space for 5-billion years before slamming into and overwhelming the space-based telescope. “This gamma-ray burst is by far the brightest light source ever seen in X-ray wavelengths at cosmological distances,” said David Burrows, senior scientist and professor of astronomy and astrophysics at Penn State University and the lead scientist for Swift’s X-ray Telescope (XRT).
A gamma-ray burst is a violent eruption of energy from the explosion of a massive star morphing into a new black hole. This mega burst, named GRB 100621A, is the brightest X-ray source that Swift has detected since the observatory began X-ray observation in early 2005.
Although Swift satellite was designed specifically to study gamma-ray bursts, the instrument was not designed to handle an X-ray blast this bright. “The intensity of these X-rays was unexpected and unprecedented” said Neil Gehrels, Swift’s principal investigator at NASA’s Goddard Space Flight Center. “Just when we were beginning to think that we had seen everything that gamma-ray bursts could throw at us, this burst came along to challenge our assumptions about how powerful their X-ray emissions can be.”.
SN 2009bb (Image Credit: NASA, Swift, Stefan Immler)
[/caption]
Are the relativistic jets of long gamma ray bursts (GRBs) produced by brand new black holes? Do some core-collapse supernovae result in black holes and relativistic jets?
The answer to both questions is ‘very likely, yes’! And what recent research points to those answers? Study of an Ic supernova (SN 2007gr), and an Ibc one (SN 2009bb), by two different teams, using archived Gamma-Ray Burst Coordination Network data, and trans-continental Very Long Baseline Interferometry (VLBI) radio observations.
“In every respect, these objects look like gamma-ray bursts – except that they produced no gamma rays,” said Alicia Soderberg at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
Soderberg led a team that studied SN 2009bb, a supernova discovered in March 2009. It exploded in the spiral galaxy NGC 3278, located about 130 million light-years away. SN 2007gr (Image Credit: Z. Paragi, Joint Institute for VLBI in Europe (JIVE))
The other object is SN 2007gr, which was first detected in August 2007 in the spiral galaxy NGC 1058, some 35 million light-years away (it’s one of the closest Ic supernovae detected in the radio waveband). The team which studied this supernova using VLBI was led by Zsolt Paragi at the Netherlands-based Joint Institute for Very Long Baseline Interferometry in Europe, and included Chryssa Kouveliotou, an astrophysicist at NASA’s Marshall Space Flight Center in Huntsville, Alabama.
The researchers searched for gamma-rays associated with the supernovae using archived records in the Gamma-Ray Burst Coordination Network located at NASA’s Goddard Space Flight Center in Greenbelt, Md. This project distributes and archives observations of gamma-ray bursts by NASA’s SWIFT spacecraft, the Fermi Gamma-ray Space Telescope and many others. However, no bursts coincided with the supernovae.
“The explosion dynamics in typical supernovae limit the speed of the expanding matter to about three percent the speed of light,” explained Kouveliotou, co-author of one of the new studies. “Yet, in these new objects, we’re tracking gas moving some 20 times faster than this.”
Unlike typical core-collapse supernovae, the stars that produce long gamma-ray bursts possess a “central engine” – likely a nascent black hole – that drives particle jets clocked at more than 99 percent the speed of light (short GRBs are likely produced by the collision/merger of two neutron stars, or a neutron star and a stellar mass black hole).
By contrast, the fastest outflows detected from SN 2009bb reached 85 percent of the speed of light and SN 2007gr reached more than 60 percent of light speed; this is “mildly relativistic”.
“These observations are the first to show some supernovae are powered by a central engine,” Soderberg said. “These new radio techniques now give us a way to find explosions that resemble gamma-ray bursts without relying on detections from gamma-ray satellites.”
The VLBI radio observations showcase how the new electronic capabilities of the European VLBI Network empower astronomers to react quickly when transient events occur. The team led by Paragi included 14 members from 12 institutions spread over seven countries, the United States, the Netherlands, Hungary, the United Kingdom, Canada, Australia and South Africa.
“Using the electronic VLBI technique eliminates some of the major issues,” said Huib Jan van Langevelde, the director of JIVE “Moreover it allows us to produce immediate results necessary for the planning of additional measurements.”
Perhaps as few as one out of every 10,000 supernovae produce gamma rays that we detect as a long gamma-ray burst. In some cases, the star’s jets may not be angled in a way to produce a detectable burst; in others, the energy of the jets may not be enough to allow them to blast through the overlying bulk of the dying star.
“We’ve now found evidence for the unsung crowd of supernovae – those with relatively dim and mildly relativistic jets that only can be detected nearby,” Kouveliotou said. “These likely represent most of the population.”
For the first time, astronomers have found a supernova explosion with properties similar to a gamma-ray burst, but without seeing any gamma rays from it. Radio observations with the Very Large Array (VLA) showed material expelled from supernova explosion SN2009bb at speeds approaching the speed of light. The superfast speeds in these rare blasts, astronomers say, are caused by an “engine” in the center of the supernova explosion that resembles a scaled-down version of a quasar. But astronomers don’t think this blast is one-of-a-kind, and say that more radio observations will point the way toward locating many more examples of these mysterious explosions.
“We think that radio observations will soon be a more powerful tool for finding this kind of supernova in the nearby Universe than gamma-ray satellites,” said Alicia Soderberg, of the Harvard-Smithsonian Center for Astrophysics.
Usually supernova explosions blasts the star’s material outward in a roughly-spherical pattern at speeds that, while fast, are only about 3 percent of the speed of light. In the supernovae that produce gamma-ray bursts, some, but not all, of the ejected material is accelerated to nearly the speed of light. Engine-driven
When the nuclear fusion reactions at the cores of very massive stars no longer can provide the energy needed to hold the core up against the weight of the rest of the star, the core collapses catastrophically into a superdense neutron star or black hole. The rest of the star’s material is blasted into space in a supernova explosion. For the past decade or so, astronomers have identified one particular type of such a “core-collapse supernova” as the cause of one kind of gamma-ray burst.
The superfast speeds in these rare blasts, astronomers say, are caused by an “engine” in the center of the supernova explosion that resembles a scaled-down version of a quasar. Material falling toward the core enters a swirling disk surrounding the new neutron star or black hole. This accretion disk produces jets of material boosted at tremendous speeds from the poles of the disk.
“This is the only way we know that a supernova explosion could accelerate material to such speeds,” Soderberg said.
Until now, no such “engine-driven” supernova had been found any way other than by detecting gamma rays emitted by it.
“Discovering such a supernova by observing its radio emission, rather than through gamma rays, is a breakthrough. With the new capabilities of the Expanded VLA coming soon, we believe we’ll find more in the future through radio observations than with gamma-ray satellites,” Soderberg said.
Why didn’t anyone see gamma rays from this explosion? “We know that the gamma-ray emission is beamed in such blasts, and this one may have been pointed away from Earth and thus not seen,” Soderberg said. In that case, finding such blasts through radio observations will allow scientists to discover a much larger percentage of them in the future.
“Another possibility,” Soderberg adds, “is that the gamma rays were ‘smothered’ as they tried to escape the star. This is perhaps the more exciting possibility since it implies that we can find and identify engine-driven supernovae that lack detectable gamma rays and thus go unseen by gamma-ray satellites.”
One important question the scientists hope to answer is just what causes the difference between the “ordinary” and the “engine-driven” core-collapse supernovae. “There must be some rare physical property that separates the stars that produce the ‘engine-driven’ blasts from their more-normal cousins,” Soderberg said. “We’d like to find out what that property is.”
One popular idea is that such stars have an unusually low concentration of elements heavier than hydrogen. However, Soderberg points out, that does not seem to be the case for this supernova.
This research will be published in January 28 issue of the journal Nature.
Fermi’s Large Area Telescope has detected bursts of gamma-rays in the binary system Cygnus X-3, which astronomers say are coming from a microquasar. While microquasars have strong emissions across is a broad range of wavelengths, this is the first time this type of object has been detected in gamma rays. “Cygnus X-3 is a genuine microquasar and it’s the first for which we can prove high-energy gamma-ray emission,” said Stéphane Corbel at Paris Diderot University in France.
n Cygnus X-3, an accretion disk surrounding a black hole or neutron star orbits close to a hot, massive star. Gamma rays (purple, in this illustration) likely arise when fast-moving electrons above and below the disk collide with the star's ultraviolet light. Fermi sees more of this emission when the disk is on the far side of its orbit. Credit: NASA's Goddard Space Flight Center
Microquasars are stellar mass object that displays in miniature some of the properties of quasars: a normal star begins shedding its matter onto either a neutron star or a black hole. This phenomenon produces large amounts of radiation and “jets” of material moving at relativistic speeds—more than 10% the speed of light—away from the star. These “relativistic jets” are a great mystery that astronomers are still trying to understand, but this new gamma-ray microquasar could provide new ways to study them.
At the center of Cygnus X-3 lies a massive Wolf-Rayet star. With a surface temperature of 100,255.372 Kelvin (180,000 degrees F,) or about 17 times hotter than the sun, the star is so hot that its mass bleeds into space in the form of a powerful outflow called a stellar wind. “In just 100,000 years, this fast, dense wind removes as much mass from the Wolf-Rayet star as our sun contains,” said Robin Corbet at the University of Maryland, Baltimore County.
The researchers matched the gamma-rays to the known orbital period of the Cygnus X-3 microquasar in order to confirm that the strong pulses of radiation were, in fact, originating from the object. They also matched the gamma-rays with radio emission from the relativistic jets of Cygnus X-3. Brighter colors indicate greater numbers of gamma rays detected in this Fermi LAT view of a region centered on the position of Cygnus X-3 (circled). The brightest sources are pulsars. Credit: NASA/DOE/Fermi LAT Collaboration
Every 4.8 hours, a compact companion embedded in a disk of hot gas wheels around the star. “This object is most likely a black hole, but we can’t yet rule out a neutron star,” Corbet said.
Between Oct. 11 and Dec. 20, 2008, and again between June 8 and Aug. 2, 2009, Cygnus X-3 was unusually active. The team found that outbursts in the system’s gamma-ray emission preceded flaring in the radio jet by roughly five days, strongly suggesting a relationship between the two.
These new findings should provide more information about the formation of such mysterious and fast-moving relativistic jets. This research appears in the 26 November issue of Science Express.
Read the team’s abstract
This image shows the afterglow of GRB 090423 (red source in the centre) and was created from images taken in the z, Y and J filters at Gemini-South and VLT (credit: A. J. Levan).
[/caption] This image shows the afterglow of GRB 090423 (red source in the centre) and was created from images taken in the z, Y and J filters at Gemini-South and VLT (credit: A. J. Levan).
On April 23, 2009 the Swift satellite detected a gamma ray burst and as we reported back in April, scientists soon realized that it was more than 13 billion light-years from Earth. GRB 090423 occurred 630 million years after the Big Bang, when the Universe was only four percent of its current age of 13.7 billion years. Now, continued observations of the GRB by astronomers around the world have yielded more information about this dramatic and ancient event: the GRB didn’t come from a monster star, but it produced a fairly sizable explosion.
Several of the world’s largest telescopes turned to the region of the sky within the next minutes and hours after Swift’s announcement of the GRB’s detection, and were able to locate the faint, fading afterglow of the GRB. Detailed analysis revealed that the afterglow was seen only in infrared light and not in the normal optical. This was the clue that the burst came from very great distance.
The Very Large Array radio telescope first looked for the object the day after the discovery, detected the first radio waves from the blast a week later, then recorded changes in the object until it faded from view more than two months later. Images of the afterglow of GRB 090423 taken (left to right) with the Y, J, H and K filters. The absence of any flux in the Y filter is a strong indication that the GRB is very high redshift (Credit: A. J. Levan & N. R. Tanvir)
Astronomers have thought that the very first stars in the Universe might be very different — brighter, hotter, and more massive — from those that formed later.
“This explosion provides an unprecedented look at an era when the Universe was very young and also was undergoing drastic changes. The primal cosmic darkness was being pierced by the light of the first stars and the first galaxies were beginning to form. The star that exploded in this event was a member of one of these earliest generations of stars,” said Dale Frail of the National Radio Astronomy Observatory.
Universe Today spoke with Edo Berger with the Gemini Telescope shortly after the GRB was detected, and he said the burst itself was not all that unusual. But even that can convey a lot of information. “That might mean that even these early generations of stars are very similar to stars in the local universe, that when they die they seem to produce similar types of gamma ray bursts, but it might be a little early to speculate.”
“This happened a little more than 13 billion years ago,” said Berger. “We’ve essentially been able to find gamma ray bursts throughout the Universe. The nearest ones are only about 100 million light years away, and this most distant one is 13 billion light years away, so it seems that they populate the entire universe. This most distant one demonstrates for the first time that massive stars exist at those very high red shifts. This is something people have suspected for a long time, but there was no direct observational proof. So that is one of the cool results from this observation.”
The scientists concluded the explosion was more energetic than most GRBs, but was certainly not the most energetic ever detected. The blast was nearly spherical that expanded into a tenuous and relatively uniform gaseous medium surrounding the star. Antennas of the Very Large Array CREDIT: NRAO/AUI/NSF
“It’s important to study these explosions with many kinds of telescopes. Our research team combined data from the VLA with data from X-ray and infrared telescopes to piece together some of the physical conditions of the blast,” said Derek Fox of Pennsylvania State University. “The result is a unique look into the very early Universe that we couldn’t have gotten any other way,” he added.
In this illustration, one photon (purple) carries a million times the energy of another (yellow). Some theorists predict travel delays for higher-energy photons, which interact more strongly with the proposed frothy nature of space-time. Yet Fermi data on two photons from a gamma-ray burst fail to show this effect. The animation below shows the delay scientists had expected to observe. Credit: NASA/Sonoma State University/Aurore Simonnet
[/caption]
While the Fermi Space Telescope has mapped the gamma ray sky with unprecedented resolution and sensitivity, it now has been able to take a measurement that has provided rare experimental evidence about the very structure of space and time, unified as space-time. Einstein’s theory of relativity states that all electromagnetic radiation travels through a vacuum at the same speed. Fermi detected two gamma ray photons which varied widely in energy; yet even after traveling 7 billion years, the two different photons arrived almost simultaneously.
On May 10, 2009, Fermi and other satellites detected a so-called short gamma ray burst, designated GRB 090510. Astronomers think this type of explosion happens when neutron stars collide. Ground-based studies show the event took place in a galaxy 7.3 billion light-years away. Of the many gamma ray photons Fermi’s LAT detected from the 2.1-second burst, two possessed energies differing by a million times. Yet after traveling some seven billion years, the pair arrived just nine-tenths of a second apart.
“This measurement eliminates any approach to a new theory of gravity that predicts a strong energy dependent change in the speed of light,” Michelson said. “To one part in 100 million billion, these two photons traveled at the same speed. Einstein still rules.”
“Physicists would like to replace Einstein’s vision of gravity — as expressed in his relativity theories — with something that handles all fundamental forces,” said Peter Michelson, principal investigator of Fermi’s Large Area Telescope, or LAT, at Stanford University in Palo Alto, Calif. “There are many ideas, but few ways to test them.” Artist concept of Fermi in space. Credit: NASA
Many approaches to new theories of gravity picture space-time as having a shifting, frothy structure at physical scales trillions of times smaller than an electron. Some models predict that the foamy aspect of space-time will cause higher-energy gamma rays to move slightly more slowly than photons at lower energy.
GRB 090510 displayed the fastest observed motions, with ejected matter moving at 99.99995 percent of light speed. The highest energy gamma ray yet seen from a burst — 33.4 billion electron volts or about 13 billion times the energy of visible light — came from September’s GRB 090902B. Last year’s GRB 080916C produced the greatest total energy, equivalent to 9,000 typical supernovae.
Lead image caption: In this illustration, one photon (purple) carries a million times the energy of another (yellow). Some theorists predict travel delays for higher-energy photons, which interact more strongly with the proposed frothy nature of space-time. Yet Fermi data on two photons from a gamma-ray burst fail to show this effect. The animation below shows the delay scientists had expected to observe. Credit: NASA/Sonoma State University/Aurore Simonnet
Artist's rendering of a black hole. Image Credit: NASA
[/caption]
Black holes get a bad rap. Most people are afraid of them, and some think black holes might even destroy Earth. Now, scientists from the University of Leeds are blaming black holes for causing the most energetic and deadly outbursts in the universe: gamma ray bursts.
The conventional model for GRBs is that a narrow beam of intense radiation is released during a supernova event, as a rapidly rotating, high-mass star collapses to form a black hole. This involves plasma being heated by neutrinos in a disk of matter that forms around the black hole. A subclass of GRBs (the “short” bursts) appear to originate from a different process, possibly the merger of binary neutron stars.
But mathematicians at the University of Leeds have come up with a different explanation: the jets come directly from black holes, which can dive into nearby massive stars and devour them.
Their theory is based on recent observations by the Swift satellite which indicates that the central jet engine operates for up to 10,000 seconds – much longer than the neutrino model can explain.
The scientists believe that this is evidence for an electromagnetic origin of the jets, i.e. that the jets come directly from a rotating black hole, and that it is the magnetic stresses caused by the rotation that focus and accelerate the jet’s flow.
For the mechanism to operate the collapsing star has to be rotating extremely rapidly. This increases the duration of the star’s collapse as the gravity is opposed by strong centrifugal forces.
One particularly peculiar way of creating the right conditions involves not a collapsing star but a star invaded by its black hole companion in a binary system. The black hole acts like a parasite, diving into the normal star, spinning it with gravitational forces on its way to the star’s centre, and finally eating it from the inside.
“The neutrino model cannot explain very long gamma ray bursts and the Swift observations, as the rate at which the black hole swallows the star becomes rather low quite quickly, rendering the neutrino mechanism inefficient, but the magnetic mechanism can,” says Professor Komissarov from the School of Mathematics at the University of Leeds.
“Our knowledge of the amount of the matter that collects around the black hole and the rotation speed of the star allow us to calculate how long these long flashes will be – and the results correlate very well with observations from satellites,” he adds.
Artist's illustration of a gamma-ray burst occurring in a dusty region of intense star formation. If a dust cloud lies between the burst and Earth, the optical light will be almost entirely absorbed, but the gamma-rays and X-rays will easily penetrate the dust. New evidence suggests that most "dark" gamma-ray bursts - those without optical afterglows - form in similar dusty environments. Credit: Aurore Simonnet/Sonoma State University, NASA Education & Public Outreach
[/caption]
Thanks to the Swift satellite and several ground based optical telescopes, astronomers are learning more about so-called “dark” gamma-ray bursts, which are bright in gamma- and X-ray emissions but with little or no visible light. These dark bursts are also providing astronomers with insights on finding areas of star formation that are hidden by dust. “Our study provides compelling evidence that a large fraction of star formation in the universe is hidden by dust in galaxies that do not appear otherwise dusty,” said Joshua Bloom, associate professor of astronomy at UC Berkeley and senior author of the study, who presented his findings at the American Astronomical Society meeting in California.
Gamma-ray bursts are the universe’s biggest explosions, capable of producing so much light that ground-based telescopes easily detect it billions of light-years away. Yet, for more than a decade, astronomers have puzzled over the nature of so-called dark bursts, which produce gamma rays and X-rays but little or no visible light. They make up roughly half of the bursts detected by NASA’s Swift satellite since its 2004 launch.
The study finds that most occur in normal galaxies detectable by large, ground-based optical telescopes.
“One possible explanation for dark bursts was that they were occurring so far away their visible light was completely extinguished,” said Bloom. Thanks to the expansion of the universe and a thickening fog of hydrogen gas at increasing cosmic distances, astronomers see no visible light from objects more than about 12.9 billion light-years away. Another possibility: Dark bursts were exploding in galaxies with unusually thick amounts of interstellar dust, which absorbed a burst’s light but not its higher-energy radiation.
Using one of the world’s largest optical telescopes, the 10-meter Keck I in Hawaii, the team looked for unknown galaxies at the locations of 14 Swift-discovered dark bursts. “For eleven of these bursts, we found a faint, normal galaxy,” said Daniel Perley, the UC Berkeley graduate student who led the study. If these galaxies were located at extreme distances, not even the Keck telescope could see them.
Most gamma-ray bursts occur when massive stars run out of nuclear fuel. As their cores collapse into a black hole or neutron star, gas jets — driven by processes not fully understood — punch through the star and blast into space. There, they strike gas previously shed by the star and heat it, which generates short-lived afterglows in many wavelengths, including visible light.
The study shows that dark bursts must be similar, except for the dusty patches in their host galaxies that obscure most of the light in their afterglows.
The astronomers surveyed 14 bursts whose optical light was either much fainter than expected or completely absent. They found that almost every “dark” gamma-ray burst has a host galaxy that is able to be detected by large optical telescopes.
Star formation occurs in dense clouds that quickly fill with dust as the most massive stars rapidly age and explode, spewing newly created elements into the interstellar medium to seed new star formation. Therefore, astronomers presume that a large amount of star formation is occurring in dust-filled galaxies, although actually measuring how much dust this process has built up in the most distant galaxies has proved extremely challenging.
The stars thought to explode as gamma-ray bursts live fast and die young. Dark bursts may represent stars that never drifted far from the dusty clouds that formed them.
Gamma-ray bursts have been detected in infrared wavelengths as far out as 13.1 billion light-years. “If gamma-ray bursts were frequent 13 billion years ago — less than a billion years after the universe formed — we ought to be detecting large numbers of them,” explained team member S. Bradley Cenko, also at UC Berkeley. “We don’t, which indicates that the first stars formed at a less frenzied pace than some models suggested.”
The astronomers conclude that less than about 7 percent of dark bursts can be occurring at such distances, and they propose radio and microwave observations of the new galaxies to better understand how their dusty regions block light. A paper on the findings has been submitted to The Astronomical Journal.
The fading infrared afterglow of GRB 090423 appears in the center of this false-color image taken with the Gemini North Telescope in Hawaii. The burst is the farthest cosmic explosion yet seen. Credit: Gemini Observatory/NSF/AURA, D. Fox and A. Cucchiara (Penn State Univ.) and E. Berger (Harvard Univ.)
[/caption]
A really, really long time ago in a galaxy far away, a massive star exploded. On April 23, 2009, the Swift satellite detected that explosion. This spectacular gamma ray burst was seen 13 billion light years away, with a redshift of 8.2, the highest ever measured. As we hinted yesterday, this object is now the most distant known object, and the burst occurred when the Universe was only 630 million years old, a mere one-twentieth of its current age. This event, called GRB 090423, can tell us much about the early Universe. “We completely smashed the record with this one,” said Edo Berger, a professor at Harvard University and a member of the team that first measured the burst’s origin. “This demonstrates for the first time that massive stars existed in the early Universe.”
At 3:55 a.m. EDT on April 23, Swift detected a ten-second-long gamma-ray burst of modest brightness, and quickly slewed around to use its Ultraviolet/Optical and X-Ray telescopes on the burst location. Swift saw a fading X-ray afterglow but nothing in visible light. A number of ground based telescopes were alerted to the event and within three hours began to observe the distant GRB.
“This was a pretty amazing event,” Berger told Universe Today. “Swift detected this gamma ray burst on April 23 and we immediately followed it up with the Gemini North Telescope in Hawaii, after it was demonstrated it did not have a visible light counterpart. That was the initial hint that this might be a distant object. We observed it in infrared and we found in the different infrared bands that there was a sharp break at a wavelength of about 1.1 microns.”
The drop-out corresponds to a redshift of 8.2 and burst distance of about 13 billion light-years.
Other telescopes that made observations were the Very Large Telescope, STFC’s United Kingdom Infrared Telescope (UKIRT), The Telescopio Nazionale Galileo (TNG), the Okayama Astrophysical Observatory, the Fermi Space Telescope and the Plateau de Bure Interferometer.
Subsequent observations the following night from other telescopes confirmed and refined the measurement. Previously, the most distant known object was a galaxy with a redshift of 6.96 discovered in 2006. The most distant GRB found September of 2008 had a redshift of 6.7. “We completely smashed the record with this one,”said Berger. “I think people were thinking it would happen step by step, but we kind of jumped things.”
Berger said the burst itself was not unusual; it was a basic a run-of-the–mill GRB. But even that can convey a lot of information. “That might mean that even these early generations of stars are very similar to stars in the local universe, that when they die they seem to produce similar types of gamma ray bursts, but it might be a little early to speculate.” Distribution of redshifts and corresponding age of the Universe for gamma-ray bursts detected by NASA's Swift satellite. The new GRB 090423 at a redshift of z=8.2 easily broke the previous record for gamma-ray bursts, and also exceeds the highest redshift galaxy and quasar discovered to date, making it the most distant known object in the Universe. GRB 090423 exploded on the scene when the Universe was only 630 million years old, and its light has been travelling to us for over 13 billion years. Credit: Edo Berger (Harvard/CfA
So what does this distant GRB tell us about the early Universe? “This happened a little more than 13 billion years ago,” said Berger. “We’ve essentially been able to find gamma ray bursts throughout the Universe. The nearest ones are only about 100 million light years away, and this most distant one is 13 billion light years away, so it seems that they populate the entire universe. This most distant one demonstrates for the first time that massive stars exist at those very high red shifts. This is something people have suspected for a long time, but there was no direct observational proof. So that is one of the cool results from this observation.”
Berger said this event also tells us that perhaps GRBs are the best objects to study which show how the early Universe evolved. “They are extremely bright and very easy to find, comparatively speaking, so they give us hope that this is the right approach. Over the years people have found high redshift quasars and galaxies, but my suspicion is that until the launch of the James Webb Space Telescope the middle of the next decade, this object will remain as the record holder. No other telescope, including the Hubble Space Telescope is capable of finding more distant objects.”
Finding this distant object also demonstrates how telescopes around the world can work together. “It’s the combination of Swift pinpointing where these objects are located and the ground-based telescopes immediately responding to these positions and then demonstrating the distance,” said Berger. “It’s really a great synergy. We’ve been doing this for a long time now, and I think part of what has been driving this is the desire to find such distant objects.
Berger said astronomers have been speculating about such distant gamma rays bursts for quite some time and there are two missions being proposed to NASA as the next generation gamma ray telescopes. So, now, the fact that we’ve now found one at such a high distance makes those satellites more attractive for funding because this has now gone from being an idea or gut feeling to real observational proof.”
Artists concept of a gamma ray burst. Credit: UC Berkeley
[/caption]
According to the Sky and Telescope blog, NASA’s Swift satellite captured a faint gamma-ray burst (GRB) last Thursday which has smashed the record for the earliest, most distant known object in the universe. Various ground-based telescopes following up on Swift’s initial detection of the GRB have measured redshifts of the object, varying from 7.6 to 8.2. Whatever the final determination is of how much this GRB’s afterglow has been redshifted by the expansion of the Universe, it will set a record. In September 2008, Swift captured GRB 080913, the most distant gamma-ray burst ever detected, with a redshift of 6.7. Astronomers using the Very Large Telescope in Chile have determined that this current GRB (090423) went off about 600 million years after the Big Bang.
A GRB comes from the cataclysmic explosion of a massive star, which could signal the birth of a black hole, a collision of two neutron stars or some other unknown phenomenon. These bursts occur approximately once per day and are brief, but intense, flashes of gamma radiation. They come from all different directions of the sky and last from a few milliseconds to a few hundred seconds.
Since the Swift satellite was launched in 2004, it has undoubtedly seen GRBs with even higher redshifts, but many bursts have afterglows so faint that astronomers are unable to determine their redshifts. The most distant galaxies with well-measured redshifts are in the 6’s.
NASA is supposed to issue a press release with more information later today, and we’ll provide an update at that time.
