Gamma Ray Bursts Archives - Page 7 of 9

October 28, 2009December 24, 2015

Einstein Still Rules, Says Fermi Telescope Team

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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.

More images and videos about the Fermi Space Telescope.

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

Source: NASA

September 18, 2009December 24, 2015

Blaming Black Holes for Gamma Ray Bursts

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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.

Source: EurekAlert

June 8, 2009December 24, 2015

“Dark” Gamma-Ray Bursts Shed Light on Star Formation

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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.

Source: NASA, UC Berkeley, AAS

April 28, 2009December 24, 2015

GRB Smashes Record for Most Distant Known Object

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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.”

Source: Interview with Edo Berger

April 27, 2009December 24, 2015

Most Distant Object Ever Seen

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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.

April 22, 2009April 26, 2016

Black Hole Jets Pack One, Two Punch in Radio, Gamma Rays

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Compact, ultrabright jets at supermassive black holes in active galaxies were already known to pack an impressive punch in radio waves. And now, an international team of scientists says they’re kicking out high-energy gamma rays too.

Distant galaxies host the super massive black holes, which are billions of times heavier than our Sun but are confined to a region no larger than our solar system. The rapidly rotating black holes attract stars, gas and dust, creating huge magnetic fields. The magnetic forces can trap some of the infalling gas and focus it into narrow jets that flow away from the core of the galaxy at velocities approaching the speed of light.

Theoreticians and observers alike have been puzzling for decades about the nature and composition of these energetic radio-emitting jets, and if they also radiate in other parts of the electromagnetic spectrum.

Some hints were provided by the EGRET instrument on the Compton Gamma Ray Observatory telescope in the late 1990s and more recent discoveries of X-ray emission made by the Chandra Observatory.

Now, astronomers from Germany, the United States and Spain have paired observations of the bright gamma-ray sky by NASA’s orbiting Fermi Gamma-ray Space Telescope with those from the ground-based Very Long Baseline Array radio telescope in the United States to observe the material expelled with enormous speeds away from the black holes in the heart of very remote galaxies. These ejections take the form of narrow jets in radio telescope images, and appear to be producing the gamma-rays detected by Fermi.

“These objects are amazing: finally we know for sure that the fastest, most compact, and brightest jets that we see with radio telescopes are the ones which are able to kick the light up to the highest energies,” said Yuri Kovalev, Humboldt Fellow and scientist at the Max Planck Institute for Radio Astronomy.

The gamma-ray bright sources are now shown to be brighter, more compact and faster at light year scales than the gamma-ray quiet sources.

Fermi, formerly known as GLAST, has been operational since the summer of 2008. The telescope records an image of the whole sky every few hours to explore the most extreme environments in the universe, including pulsars and gamma-ray bursts, as well as black holes in galactic nuclei. Gamma-ray observations alone are not enough to discern the exact location of the radiation, however. The VLBA serves as a magnifying glass for zeroing in on the most energetic processes in the distant universe. Many objects found by Fermi to be extreme in gamma-rays are emitting strong bursts of radio emission at the same time.

The Very Long Baseline Array is a continent-wide system of ten radio telescope antennas, ranging from Hawaii in the west to the U.S. Virgin Islands in the east. Dedicated in 1993, the VLBA is operated by the U.S. National Radio Astronomy Observatory and is designed to monitor the brightest objects in the Universe at the highest available resolution in astronomy.

The work for astronomers does not stop here: the team has concluded that the region of the jet closest to the black hole is undoubtedly the place where the gamma-ray and the radio bursts of light originate in about the same time. However, some parts of the puzzle have yet to be resolved, they say: some bright gamma-ray sources in the sky appear to have no radio or optical counterpart — their nature is still completely unknown.

Source: Max-Planck Institute. The findings are being reported in two publications in the May 1, 2009 issue of Astrophysical Journal Letters (here and here).

Links:

Very Long Baseline Array
VLBA Monitoring of AGN Jets: The MOJAVE Project
Fermi Gamma-ray Space Telescope LAT Group

April 6, 2009April 6, 2009

Now Showing: Fermi All-Sky Movie

This could be titled “87 Days of Fermi,” or “Blazing Galaxies:” This movie is made from the first 87 days of data gathered by Fermi’s Large Area Telescope (LAT), showing all the gamma ray sources detected so far, with active galaxies called blazars flaring and fading in this all-sky movie. “The movie shows counts of gamma rays seen by Fermi’s LAT, and each frame shows the gamma rays collected in one day,” said Elizabeth Hays, an astrophysicist on the Fermi team. Visible are rapid and dramatic flashes, which underscores one of the most valuable things Fermi does. “We watch the sky all the time and alert other telescopes, in space and on the ground, when something interesting is going on,” Hays said.
Continue reading “Now Showing: Fermi All-Sky Movie”

April 3, 2009December 24, 2015

Integral Dissects Super-Bright Gamma Ray Burst

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The European Space Agency’s Integral spacecraft has captured one of the brightest gamma-ray bursts ever seen. In looking at the data, astronomers have been able to investigate the initial phases of this giant stellar explosion, which ejected matter at velocities close to the speed of light. Astronomers also believe the explosion lifted a piece of the central engine’s magnetic field into space. The GRB reached Earth on December 19, 2004, and since then the Integral team has been meticulously dissecting the data.

Integral, an orbiting gamma-ray observatory, recorded the entire 2004 GRB event, providing information for what may prove to be one of the most important gamma-ray bursts (GRBs) seen in recent years. As the data was collected, astronomers saw the 500-second-long burst rise to extraordinary brilliance.

“It is in the top 1% of the brightest GRBs we have seen,” says Diego Götz, CEA Saclay, France, who headed the investigation.

The brightness of the event, known as GRB 041219A, has allowed the team to investigate the polarization of the gamma rays. Polarization refers to the preferred direction in which the radiation wave oscillates. For example Polaroid sunglasses work with visible light by letting through only a single direction of polarization, blocking most of the light from entering our eyes.

This artist's impression shows the centre of a dying star collapsing minutes before the star implodes. The blast from a Gamma Ray Burst is thought to be produced by a jet of fast-moving gas that bursts from near the central engine; probably a black hole created by such a collapse of the massive star. Credits: NASA/Dana Berry

The team has shown that the gamma rays were highly polarized and varied tremendously in level and orientation.

The blast from a GRB is thought to be produced by a jet of fast-moving gas bursting from near the central engine; probably a black hole created by the collapse of the massive star. The polarization is directly related to the structure of the magnetic field in the jet. So it is one of the best ways for astronomers to investigate how the central engine produces the jet. Götz said there are a number of ways this might happen.

In the first scenario, the jet carries a portion of the central engine’s magnetic field into space. A second involves the jet generating the magnetic field far from the central engine. A third concerns the extreme case in which the jet contains no gas just magnetic energy, and a fourth scenario entails the jet moving through an existing field of radiation.

In each of the first three scenarios, the polarization is generated by what is called synchrotron radiation. The magnetic field traps particles, known as electrons, and forces them to spiral, releasing polarized radiation. In the fourth scenario, the polarization is imparted through interactions between the electrons in the jet and photons in the existing radiation field.

Götz believes that the Integral results favor a synchrotron model and, of those three, the most likely scenario is the first, in which the jet lifts the central engine’s magnetic field into space. “It is the only simple way to do it,” he says.

What Götz would most like to do is measure the polarization for every GRB, to see whether the same mechanism applies to all. Unfortunately, many GRBs are too faint for the current instrumentation to succeed. Even the state-of-the-art IBIS instrument on Integral can only record the polarization state of gamma rays if a celestial source is as bright as GRB 041219A.

“So, for now we just have to wait for the next big one,” he says.

Source: ESA

March 2, 2009April 26, 2016

Swift Satellite Catches Early Stages of GRB

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Astronomers have now been able to see the very early stages of a gamma ray burst, thanks to the Swift satellite. The Ultraviolet/Optical Telescope (UVOT) on board the satellite provided an ultraviolet spectrum of a GRB just 251 seconds after its onset – the earliest ever captured. Further use of the instrument in this way will also allow distance and brightness of GRBs to be calculated within a few hundred seconds of their initial outburst, as well as gather new information about the causes of bursts and the galaxies they originate from.

“The UVOT’s wavelength range, coupled with the fact that Swift is a space observatory with a speedy response rate, unconstrained by time of day or weather, has allowed us to collect this early ultraviolet spectrum,” said Martin Still from the Mullard Space Science Laboratory (MSSL) at UCL.

“By looking at these earlier moments of gamma ray bursts,” said Paul Kuin, another member of the team, “we will not only be able to better calculate things such as the luminosity and distance of a burst, but to find out more about the galaxies that play host to them and the impact these explosions have on their environments. Once this new technique is applied to much brighter bursts, we’ll have a wealth of new data.”

Massimiliano De Pasquale, a GRB scientist of the UVOT team, added, “The UVOT instrument is particularly suited to study bursts with an average to high redshift – a part of the ultraviolet spectrum that is difficult for even the very big ground-based telescopes to study. Using UVOT with Swift, we can now find redshifts for bursts that were difficult to capture in the past and find out more about their distant host galaxies, about ten billion light years away.”

Since its launch in 2004, the Swift satellite has provided the most comprehensive study so far of GRBs and their afterglows. Using the UVOT to obtain ultraviolet spectrums, the Swift team will be able to build on this study and even determine more about the host galaxies’ chemistry.

Paul Kuin said, “The new spectrum has not only allowed us to determine the distance of the gamma ray burst’s host galaxy but has revealed the density of its hydrogen clouds. Learning more about these far-away galaxies helps us to understand how they formed during the early universe. The gamma ray burst observed on this occasion originated in a galaxy 8 billion light years from Earth.”

Swift is a NASA mission in collaboration with the Science and Technology Facilities Council (STFC) in the UK and the Italian Space Agency (ASI). The work was published on Friday 27th February in the Monthly Notices of the Royal Astronomical society.

Source: Science and Technology Facilities Council

February 19, 2009December 24, 2015

Fermi Glimpses Wildest-Ever Gamma-Ray Blast

GRB 080916C’s X-ray afterglow appears orange and yellow in this view that merges images from Swift’s UltraViolet/Optical and X-ray telescopes. Credit: NASA/Swift/Stefan Immler

Researchers using the Fermi Gamma-ray Space Telescope are reporting a gamma-ray explosion that blows away anything they’ve seen before. The blast, recorded last fall in the constellation Carina, released the energy of 9,000 supernovae.

The collapse of very massive stars can produce violent explosions, accompanied by strong bursts of gamma-ray light, which are some of the brightest events in the universe. Typical gamma-ray bursts emit photons with energies between 10 kiloelectron volts and about 1 megaelectron volt. Photons with energies above megaelectron volts have been seen in some very rare occasions but the distances to their sources were not known. An international research consortium is reporting in this week’s issue of the journal Science Express that the Fermi Gamma-Ray Space Telescope has detected photons with energies between 8 kiloelectron volts and 13 gigaelectron volts arriving from the gamma-ray burst 080916C.

formerly_glast — Fermi, formerly known as GLAST, pictured pre-launch in the spring of 2008. Photo credit: NASA/Dimitri Gerondidakis

The explosion, designated GRB 080916C, occurred just after midnight GMT on September 16 (7:13 p.m. on the 15th in the eastern US). Two of Fermi’s science instruments — the Large Area Telescope and the Gamma-ray Burst Monitor — simultaneously recorded the event. Together, the two instruments provide a view of the blast’s gamma-ray emission from energies ranging from 3,000 to more than 5 billion times that of visible light.

A team led by Jochen Greiner at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, established that the blast occurred 12.2 billion light-years away using the Gamma-Ray Burst Optical/Near-Infrared Detector (GROND) on the 2.2-meter (7.2-foot) telescope at the European Southern Observatory in La Silla, Chile.

“Already, this was an exciting burst,” says Julie McEnery, a Fermi deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “But with the GROND team’s distance, it went from exciting to extraordinary.”

Astronomers believe most gamma-ray explosions occur when exotic massive stars run out of nuclear fuel. As a star’s core collapses into a black hole, jets of material — powered by processes not yet fully understood — blast outward at nearly the speed of light. The jets bore all the way through the collapsing star and continue into space, where they interact with gas previously shed by the star. This generates bright afterglows that fade with time.

The burst is not only spectacular but also enigmatic: a curious time delay separates its highest-energy emissions from its lowest. Such a time lag has been seen clearly in only one earlier burst, and researchers have several explanations for why it may exist. It is possible that the delays could be explained by the structure of this environment, with the low- and high-energy gamma rays “coming from different parts of the jet or created through a different mechanism,” said Large Area Telescope Principal Investigator Peter Michelson, a Stanford University physics professor affiliated with the Department of Energy.

Another, far more speculative theory suggests that perhaps time lags result not from anything in the environment around the black hole, but from the gamma rays’ long journey from the black hole to our telescopes. If the theorized idea of quantum gravity is correct, then at its smallest scale space is not a smooth medium but a tumultuous, boiling froth of “quantum foam.” Lower-energy (and thus lighter) gamma rays would travel faster through this foam than higher-energy (and thus heavier) gamma rays. Over the course of 12.2 billion light years, this very small effect could add up to a significant delay.

The Fermi results provide the strongest test to date of the speed of light’s consistency at these extreme energies. As Fermi observes more gamma-ray bursts, researchers can look for time lags that vary with respect to the bursts. If the quantum gravity effect is present, time lags should vary in relation to the distance. If the environment around the burst origin is the cause, the lag should stay relatively constant no matter how far away the burst occurred.

“This one burst raises all sorts of questions,” Michelson says. “In a few years, we’ll have a fairly good sample of bursts, and may have some answers.”

Source: Eurekalert