Posted on by Tim Reyes

New Analysis Sets a Space & Time Zone for Complex Life

A new research paper reveals more details of the effect gamma ray bursts (GRB) have had on the development of complex life throughout the cosmos. Illustration depicts a beam from a GRB as might have been directed toward early life on Earth during the Cambrian or Ordovician periods, ~500 million years ago. (Illustration Credit: T. Reyes)

If too close to an environment harboring complex life, a gamma ray burst could spell doom for that life. But could GRBs be the reason we haven’t yet found evidence of other civilizations in the cosmos? To help answer the big question of “where is everybody?” physicists from Spain and Israel have narrowed the time period and the regions of space in which complex life could persist with a low risk of extinction by a GRB.

GRBs are some of the most cataclysmic events in the Universe. Astrophysicists are astounded by their intensity, some of which can outshine the whole Universe for brief moments. So far, they have remained incredible far-off events. But in a new paper, physicists have weighed how GRBs could limit where and when life could persist and evolve, potentially into intelligent life.

In their paper, “On the role of GRBs on life extinctions in the Universe”, published in the journal Science, Dr. Piran from Hebrew University and Dr. Jimenez from University of Barcelona consider first what is known about gamma ray bursts. The metallicity of stars and galaxies as a whole are directly related to the frequency of GRBs. Metallicity is the abundance of elements beyond hydrogen and helium in the content of stars or whole galaxies. More metals reduce the frequency of GRBs. Galaxies that have a low metal content are prone to a higher frequency of GRBs. The researchers, referencing their previous work, state that observational data has shown that GRBs are not generally related to a galaxy’s star formation rate; forming stars, including massive ones is not the most significant factor for increased frequency of GRBs.

As fate would have it, we live in a high metal content galaxy – the Milky Way. Piran and Jimenez show that the frequency of GRBs in the Milky Way is lower based on the latest data available. That is the good news. More significant is the placement of a solar system within the Milky Way or any galaxy.

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
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

The paper states that there is a 50% chance of a lethal GRB’s having occurred near Earth within the last 500 million years. If a stellar system is within 13,000 light years (4 kilo-parsecs) of the galactic center, the odds rise to 95%. Effectively, this makes the densest regions of all galaxies too prone to GRBs to permit complex life to persist.

The Earth lies at 8.3 kilo-parsecs (27,000 light years) from the galactic center and the astrophysicists’ work also concludes that the chances of a lethal GRB in a 500 million year span does not drop below 50% until beyond 10 kilo-parsecs (32,000 light years). So Earth’s odds have not been most favorable, but obviously adequate. Star systems further out from the center are safer places for life to progress and evolve. Only the outlying low star density regions of large galaxies keep life out of harm’s way of gamma ray bursts.

The paper continues by describing their assessment of the effect of GRBs throughout the Universe. They state that only approximately 10% of galaxies have environments conducive to life when GRB events are a concern. Based on previous work and new data, galaxies (their stars) had to reach a metallicity content of 30% of the Sun’s, and the galaxies needed to be at least 4 kilo-parsecs (13,000 light years) in diameter to lower the risk of lethal GRBs. Simple life could survive repeated GRBs. Evolving to higher life forms would be repeatedly set back by mass extinctions.

Piran’s and Jimenez’s work also reveals a relation to a cosmological constant. Further back in time, metallicity within stars was lower. Only after generations of star formation – billions of years – have heavier elements built up within galaxies. They conclude that complex life such as on Earth – from jelly fish to humans – could not have developed in the early Universe before Z > 0.5, a cosmological red-shift equal to ~5 billion years ago or longer ago. Analysis also shows that there is a 95% chance that Earth experienced a lethal GRB within the last 5 billion years.

The question of what effect a nearby GRB could have on life has been raised for decades. In 1974, Dr. Malvin Ruderman of Columbia University considered the consequences of a nearby supernova on the ozone layer of the Earth and on terrestrial life. His and subsequent work has determined that cosmic rays would lead to the depletion of the ozone layer, a doubling of the solar ultraviolet radiation reaching the surface, cooling of the Earth’s climate, and an increase in NOx and rainout that effects biological systems. Not a pretty picture. The loss of the ozone layer would lead to a domino effect of atmospheric changes and radiation exposure leading to the collapse of ecosystems. A GRB is considered the most likely cause of the mass extinction at the end of the Ordovician period, 450 million years ago; there remains considerable debate on the causes of this and several other mass extinction events in Earth’s history.

The paper focuses on what are deemed long GRBs – lGRBs – lasting several seconds in contrast to short GRBs which last only a second or less. Long GRBs are believed to be due to the collapse of massive stars such as seen in supernovas, while sGRBs are from the collision of neutron stars or black holes. There remains uncertainty as to the causes, but the longer GRBs release far greater amounts of energy and are most dangerous to ecosystems harboring complex life.

The paper narrows the time and space available for complex life to develop within our Universe. Over the age of the Universe, approximately 14 billion years, only the last 5 billion years have been conducive to the creation of complex life. Furthermore, only 10% of the galaxies within the last 5 billion years provided such environments. And within only larger galaxies, only the outlying areas provided the safe distances needed to evade lethal exposure to a gamma ray burst.

This work reveals how well our Solar System fits within the ideal conditions for permitting complex life to develop. We stand at a fairly good distance from the Milky Way’s galactic center. The age of our Solar System, at approximately 4.6 billion years, lies within the 5 billion year safe zone in time. However, for many other stellar systems, despite how many are now considered to exist throughout the Universe – 100s of billions in the Milky Way, trillions throughout the Universe – simple is probably a way of life due to GRBs. This work indicates that complex life, including intelligent life, is likely less common when just taking the effect of gamma ray bursts into consideration.

References:

On the role of GRBs on life extinction in the Universe, Tsvi Piran, Raul Jimenez, Science, Nov 2014, pre-print

Posted on by Nancy Atkinson

Update: Possible ‘Nearby’ Gamma Ray Burst Alert Was False Alarm

Color view of M31 (The Andromeda Galaxy), with M32 (a satellite galaxy) shown to the lower left. Credit and copyright: Terry Hancock.

Following the late night news yesterday of a possible gamma ray burst in our next door neighboring galaxy Andromeda, it was an “Oh darn!” moment this morning to find out the big event was likely a false alarm. The false alert — and the ensuing false excitement — was due to an unlikely combination of Swift’s Burst Alert Telescope (BAT) detecting what was a previously known object and a power outage at Goddard Space Flight Center and Swift Data Center, so that the data couldn’t be analyzed by the regular team of astronomers around the world.

Also, according to a blog post by Phil Evans, a post-doctoral research assistant from the University of Leicester and a member of the support team for Swift, the Swift team never actually announced a claim of such an event, and it turns out that the tentative data that triggered this story was overstated.

“Interestingly, the Swift team never claimed it was [a GRB]; indeed, I haven’t seen any professional communication claiming that this was a GRB,” Evans wrote on his blog. “Why it has been reported throughout the web as a GRB is something I can only speculate on, but Swift has been fabulously successful studying GRBs.”

Definitely read Evans’ entire analysis of the event.

A circular posted from the Swift-XRT team” on NASA’s Gamma-ray Coordinates Network (GCN) system at says that the astronomers “do not believe this source to be in outburst”. On the Nature blog, Alexandra Witze spoke with Swift team member Kim Page, also from the University of Leicester, who told Nature “that the source had been initially mistaken for a new outburst, and that its intensity had been overestimated due to measurement error. Instead, she says, it was a relatively common, persistent x-ray source — possibly a globular cluster — that had previously been catalogued.”

Here’s the circular in its entirety:

We have re-analysed the prompt XRT data on Swift trigger 600114 (GCN Circ.
16332), taking advantage of the event data.

The initial count rate given in GCN Circ. 16332 was based on raw data from
the full field of view, without X-ray event detection, and therefore may
have been affected by other sources in M31, as well as background hot
pixels. Analysis of the event data (not fully available at the time of the
initial circular) shows the count rate of the X-ray source identified in
GCN Circ. 16332 to have been 0.065 +/- 0.012 count s^-1, consistent with
the previous observations of this source [see the 1SXPS catalogue (Evans
et al. 2014): http://www.swift.ac.uk/1SXPS/1SXPS%20J004143.1%2B413420].

We therefore do not believe this source to be in outburst. Instead, it was
a serendipitous constant source in the field of view of a BAT subthreshold
trigger.

This circular is an official product of the Swift-XRT team.

The event caused a tweet-storm last night on Twitter (see #GRBM31) and as many have said, the excitement was magnified because of the ability to spread news quickly via social media:

Astronomer Robert Rutledge, who publishes the Astronomer’s Telegram has given a Tweet-by-Tweet analysis of what happened with the false alarm:

Posted on by Nancy Atkinson

Possible Gamma Ray Burst Detected in Andromeda, Would be Closest Ever Observed

Raw data showing the raw gamma ray light curve from a possible Gamma Ray Burst in M31 on May 27, 2014 obtained by the Swift Burst Alert Telescope. Credit: Goddard Space Flight Center/NASA

Update (5/28/14 9:20 am EDT): This alert may have been a false alarm. Further analysis showed the initial brightness was overestimated by a factor of 300. An official circular from the Swift-XRT team says “therefore do not believe this source to be in outburst. Instead, it was a serendipitous constant source in the field of view of a BAT subthreshold trigger.” Please read our subsequent article here that provides further information and analysis.

Something went boom in the Andromeda Galaxy, our next door neighbor. The Swift Gamma-Ray Burst telescope detected a sudden bright emission of gamma rays. Astronomers aren’t sure yet if it was a Gamma-Ray Burst (GRB) or an Ultraluminous X-Ray (ULX) or even an outburst from a low-mass x-ray binary (LMXB), but whatever it turns out to be, it will be the closest event of this kind that we’ve ever observed.

One of the previous closest GRBs was 2.6 billion light-years away, while Andromeda is a mere 2.5 million light years away from Earth. Even though this would be the closest burst to Earth, there is no danger of our planet getting fried by gamma rays.

According to astronomer (Bad Astronomer!) Phil Plait, a GRB would have to be less than 8,000 light years away cause any problems for us.

Andromeda Galaxy. Credit: NASA
Andromeda Galaxy. Credit: NASA

This event is providing astronomers with a rare opportunity to gain information vital to understanding powerful cosmic explosions like this.

If it is a GRB, it likely came from a collision of neutron stars. If it is a ULX, the blast came from a black hole consuming gas. If the outburst was from a LMXB, a black hole or neutron star annihilated its companion star.
Astronomers should be able to determine the pedigree of this blast within 24-48 hours by watching the way the light fades from the burst.

How this Blast was Detected

The Swift Burst Alert telescope watches the sky for gamma-ray bursts and, within seconds of detecting a burst Swift relays the location of the burst to ground stations, allowing both ground-based and space-based telescopes around the world the opportunity to observe the burst’s afterglow. As soon as it can, Swift will swiftly shift itself to observe the burst with its X-ray and ultraviolet telescopes.

The burst alert came at 21:21 pm Universal time on May 27, 2014; three minutes later, the X-ray telescope aboard Swift was observing a bright X-ray glow.

News of the event quickly spread across the astronomical community and on Twitter, sending astronomers scrambling for their telescopes.

According to astronomer Katie Mack on Twitter, if this is indeed a GRB, this gamma-ray burst looks like a short GRB.

No two GRBs are the same, but they are usually classified as either long or short depending on the burst’s duration. Long bursts are more common and last for between 2 seconds and several minutes; short bursts last less than 2 seconds, meaning the action can all be over in just milliseconds.

As we noted earlier, more should be known about this blast within a day or so and we’ll keep you posted. In the meantime, you can follow the hashtag #GRBM31 on Twitter to see the latest. Katie Mack or Robert Rutledge (Astronomer’s Telegram) have been tweeting pertinent info about the burst.

Posted on by Fraser Cain

Weekly Space Hangout – August 9, 2013

Gather round the internets for another episode of the Weekly Space Hangout. Where our experienced team of journalists, astronomers and astronomer-journalists bring you up to speed on the big happenings in the universe of space and astronomy.

Our team this week:

Reporters: Casey Dreier, David Dickinson, Amy Shira Teitel, Sondy Springmann, Nicole Gugliuci

Host: Fraser Cain

And here are the stories we covered:
Curiosity Celebrates One Year on Mars
2013 Perseids Meteor Shower
Lori Garver Leaving NASA
Kilonova Discovered
Sun’s Magnetic Field is About to Flip
Japanese HTV-4 Docked
MAVEN Update

We record the Weekly Space Hangout every Friday at Noon Pacific, 3 pm Eastern. Join us live here on Universe Today, over on our YouTube account, or on Google+. Or you can watch the archive after the fact.

Posted on by David Dickinson

Amateur Astronomer Catches Record Setting Gamma-Ray Burst

Vigilance and a little luck paid off recently for an amateur astronomer.

On April 27th, 2013 a long lasting gamma-ray burst was recorded in the northeastern section of the constellation Leo. As reported here on Universe Today, the burst was the most energetic ever seen, peaking at about 94 billion electron volts as seen by Fermi’s Large Area Telescope. In addition to Fermi’s Gamma Ray Burst Monitor, the Swift satellite and a battery of ground based instruments also managed to quickly swing into action and record the burst as it was underway.

Patrick Wiggins' capture of the optical counterpart to GRB 130427A with extrapolated light curve. Note that the Moon was just two days past Full in the direction of the constellation Libra at the time, hence the sky glow! (Credit: Patrick Wiggins).
Patrick Wiggins’ capture of the optical counterpart to GRB 130427A with extrapolated light curve. Note that the Moon was just two days past Full in the direction of the constellation Libra at the time, hence the sky glow! (Credit: Patrick Wiggins).

But professionals weren’t the only ones to capture the event. Amateur astronomer Patrick Wiggins was awake at the time, doing routine observations from his observatory based near Toole, Utah when the alert message arrived. He quickly swung his C-14 telescope  into action at the coordinates of the burst at 11 Hours 32’ and 33” Right Ascension and +27° 41’ 56” declination.

Wiggins then began taking a series of 60-second exposures with his SBIG ST-10XME imager and immediately found something amiss. A 13th magnitude star had appeared in the field. At first, Wiggins believed this was simply too bright to be a gamma-ray burst transient, but he continued to image the field into the morning of April 27th.

Wiggins had indeed caught his optical prey, the very first gamma-ray burst he’d captured. And what a burst it was. At only 3.6 billion light years distant, GRB 130427A (gamma-ray bursts are named after the year-month-day of discovery) was one for the record books, and in the top five percent of the closest bursts ever observed.

Mr. Wiggins further elaborated the fascinating story of the observation to Universe Today:

“I was imaging an area near where the burst occurred and received an email GCN Circular and a GCN/SWIFT Notice of the event within minutes of it happening.  As bad luck would have it I was in the kitchen fixing a late night snack when both arrived so I was about 10 minutes late reading them.

I figured that 10 minutes was way too late as these things typically only last a minute or two but I slewed to the coordinates indicated in the notices and shot a quick picture.  There was a bright “something” in the middle of the frame as shown here with the POSS comparison image:”

POSS comparison image of the field of GRB 130427A. (Credit: Partick Wiggins).
POSS comparison image of the field of GRB 130427A. (Credit: Partick Wiggins).

“But I thought it looked way too bright for a GRB so I moved the telescope slightly (to see if the object was a ghost or an artifact in the system) and shot again but it was still there.

A quick check of the POSS showed nothing should be there so I started shooting pictures at five minute intervals until dawn and it was those images I used to put together the light curve:”

Expanded light curve of GRB 130427A. (Credit: Patrick Wiggins).
Expanded light curve of GRB 130427A. (Credit: Patrick Wiggins).

Amazingly, the RAPTOR (RAPid Telescopes for Optical Response) array recorded a peak brightness in optical wavelengths of magnitude +7.4 just less than a minute before the Swift spacecraft swung into action. This is just below the dark sky limiting naked-eye magnitude of +6. This is also just below the record optical brightness set by GRB 080319B, which briefly reached magnitude +5.3 back in 2008.

RAPTOR-K & RAPTOR-T based at the Fenton Hill Observatory in New Mexico. (Credit: NNSA/Los Alamos National Laboratory/Dept. of Energy).
RAPTOR-K & RAPTOR-T based at the Fenton Hill Observatory in New Mexico. (Credit: NNSA/Los Alamos National Laboratory/Dept. of Energy).

RAPTOR is run by the Los Alamos National Laboratory and is based at Fenton Hill Observatory in the Jemez Mountains of New Mexico 56 kilometres west of Los Alamos.

The Catalina Real-Time Transient Survey based outside of Tucson Arizona also detected the burst independently, giving it the designation CSS130502: 113233+274156. The burst occurred less than a degree from the +13th magnitude galaxy NGC 3713, and the galaxy SDSS J113232.84+274155.4 is also very close to the observed position of the burst.

Mr. Wiggins’ observation also raises an intriguing possibility. Did anyone catch a surreptitious image of the burst? Anyone wide-field imaging right around the three-way junction of the constellations Ursa Major, Leo & Leo Minor at the correct time might just have caught GRB 130427A in the act. Make sure to review those images!

Follow up observations of gamma-ray bursts are just one of the ways that amateur backyard observers continue to contribute to the science of astronomy. Observers such as Mr. Wiggins and James McGaha based at the Grasslands Observatory near Sonita, Arizona routinely swing their equipment into action chasing after optical transients as alert messages for gamma-ray events are received.

Gamma-ray bursts where first discovered in 1967 by the Vela spacecraft designed to monitor nuclear weapons testing during the Cold War. They come in two varieties: short period and long duration bursts. Short period bursts of less than two seconds duration are thought to occur when a binary pulsar pair merges, while long duration bursts such as GRB 130427A occur when a massive red giant star undergoes a core collapse and shoots a high energy jet directly along its poles in a hypernova explosion. If the burst is aimed in our direction, we get to see the event. Thankfully, no possible progenitors of a long duration gamma-ray burst lie aimed at us in our galaxy, though the Wolf-Rayet stars Eta Carinae and WR 104 both about 8,000 light years distant are worth keeping an eye on. Luckily, neither of these massive stars is known to have rotational poles tipped in our general direction.

Scary stuff to consider as we hunt for the next “Big One” in the night sky. In the meantime, we’ve got much to learn from gamma-ray bursts such as GRB 130427A. Congrats to Mr. Wiggins on his first gamma-ray burst observation… the event was made all the more special by the fact that it occurred on his birthday!

-Mr Patrick Wiggins is NASA/JPL Ambassador to the state of Utah.

– Read the American Association of Variable Star Observers (AAVSO) report of the light curve of GRB 130427A as reported by Mr. Wiggins here.

– NASA’s Goddard Space Flight Center maintains a clearing house of the latest GRB alerts in near-real-time here.

– You can also now receive GRB alerts via @Gammaraybursts on Twitter, as well as follow NASA’s Swift and Fermi missions.

– And of course, “there’s an App for that” in the world of GRB alerts in the form of the free Swift Explorer App for the Iphone.

Posted on by Fraser Cain

Weekly Space Hangout – May. 3, 2013

Another busy episode of the Weekly Space Hangout, with more than a dozen space stories covered by a collection of space journalists. This week’s panel included Alan Boyle, Dr. Nicole Gugliucci, Amy Shira Teitel, David Dickinson, Dr. Matthew Francis, and Jason Major. Hosted by Fraser Cain. We discussed:

We record the Weekly Space Hangout every Friday at 12 pm Pacific / 3 pm Eastern. You can watch us live on Google+, Cosmoquest or listen after as part of the Astronomy Cast podcast feed (audio only).

Posted on by Fraser Cain

Weekly Space Hangout – January 25, 2013

Back by popular demand… the Weekly Space Hangout has returned. This is a weekly broadcast on Google+, where I’m joined by a wide and varied team of space and astronomy journalists to discuss the big breaking stories this week.

This week, we talked about:

We record the Weekly Space Hangout every Friday on Google+ at 12:00 pm PST / 3:00 pm EST / 2000 GMT. You’ll want to circle Cosmoquest on Google+ to find out when we’re recording next. The audio for the Weekly Space Hangout is also released to the Astronomy Cast podcast feed.

Posted on by Jason Major

X-ray Burst May Be the First Sign of a Supernova

GRB 080913, a distant supernova detected by Swift. This image merges the view through Swift’s UltraViolet and Optical Telescope, which shows bright stars, and its X-ray Telescope. Credit: NASA/Swift/Stefan Immler

The first moments of a massive star going supernova may be heralded by a blast of x-rays, detectable by space telescopes like Swift, which could then tell astronomers where to look for the full show in gamma rays and optical wavelengths. These findings come from the University of Leicester in the UK where a research team was surprised by the excess of thermal x-rays detected along with gamma ray bursts associated with supernovae.

“The most massive stars can be tens to a hundred times larger than the Sun,” said Dr. Rhaana Starling of the University of Leicester  Department of Physics and Astronomy. “When one of these giants runs out of hydrogen gas it collapses catastrophically and explodes as a supernova, blowing off its outer layers which enrich the Universe.

“But this is no ordinary supernova; in the explosion narrowly confined streams of material are forced out of the poles of the star at almost the speed of light. These so-called relativistic jets give rise to brief flashes of energetic gamma-radiation called gamma-ray bursts, which are picked up by monitoring instruments in space, that in turn alert astronomers.”

Powerful gamma ray bursts — GRBs — emitted from supernovae can be detected by both ground-based observatories and NASA’s Swift telescope. Within seconds of detecting a burst (hence its name) Swift relays its location to ground stations, allowing both ground-based and space-based telescopes around the world the opportunity to observe the burst’s afterglow.

But the actual moment of the star’s collapse, when its collapsing core reacts with its surface, isn’t observed — it happens too quickly, too suddenly. If these “shock breakouts” are the source of the excess thermal x-rays (a.k.a. black body emission) that have been recently identified in Swift data, some of the galaxy’s most energetic supernovae could be pinpointed and witnessed at a much earlier moment in time — literally within the first seconds of their birth.

“This phenomenon is only seen during the first thousand seconds of an event, and it is challenging to distinguish it from X-ray emission solely from the gamma-ray burst jet,” Dr. Starling said. “That is why astronomers have not routinely observed this before, and only a small subset of the 700+ bursts we detect with Swift show it.”

Read more: Finding the Failed Supernovae

More observations will be needed to determine if the thermal emissions are truly from the initial collapse of stars and not from the GRB jets themselves. Even if the x-rays are determined to be from the jets it will provide valuable insight to the structure of GRBs… “but the strong association with supernovae is tantalizing,” according to Dr. Starling.

Read more on the University of Leicester press release here, and see the team’s paper in the Nov. 28 online issue of the Monthly Notices of the Royal Astronomical Society here (Full PDF on arXiv.org here.)

Inset image: An artist’s rendering of the Swift spacecraft with a gamma-ray burst going off in the background. Credit: Spectrum Astro. Find out more about the Swift telescope’s instruments here.

 

Posted on by Mike Simonsen

Solving the Mystery of Dark Gamma Ray Bursts

Artists impression of a dark gamma-ray burst. Credit: ESO

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Unraveling the mystery of Gamma Ray Bursts (GRBs) is a story filled with international intrigue, fantastic claims, serious back-tracking, and incremental improvements in our understanding of the true nature and implications of the most energetic, destructive forces in the Universe. New results from a team of scientists studying so-called “dark gamma-ray bursts” have firmly snapped a new piece into the GRB puzzle. This research is presented in a paper to appear in the journal Astronomy & Astrophysics on December 16, 2010.

The discovery of GRBs was an unexpected result of the American space program and the military keeping tabs on the Russians to verify compliance with a cold war nuclear test ban treaty. In order to be sure the Russians weren’t detonating nuclear weapons on the far side of the Moon, the 1960’s era Vela spacecraft were equipped with gamma ray detectors. The Moon might shield the obvious signature of x-rays from the far side, but gamma rays would penetrate right through the Moon and would be detectible by the Vela satellites.

By 1965, it became apparent that events which triggered the detectors but were clearly not signatures of nuclear detonations, so they were carefully, and secretly, filed away for future study. In 1972, astronomers were able to deduce the directions to the events with sufficient accuracy to rule out the Sun and Earth as sources. They came to the conclusion that these gamma-ray events were “of cosmic origin”. In 1973, this discovery was announced in the Astrophysical Journal.

This created quite stir in the astronomical community and dozens of papers on GRBs and their causes began appearing in the literature. Initially, most hypothesized the origin of these events came from within our own galaxy. Progress was painfully slow until the 1991 launch of the Compton Gamma Ray Observatory. This satellite provided crucial data indicating that the distribution of GRBs is not biased towards any particular direction in space, such as toward the galactic plane or the center of the Milky Way Galaxy. GRBs came from everywhere all around us. They are “cosmic” in origin. This was a big step in the right direction, but created more questions.

For decades, astronomers searched for a counterpart, any astronomical object coincident with a recently observed burst. But the lack of precision in the location of GRBs by the instruments of the day frustrated attempts to pin down the sources of these cosmic explosions. In 1997, BeppoSAX detected a GRB in x-rays shortly after an event and the optical after glow was detected 20 hours later by the William Herschel Telescope. Deep imaging was able to identify a faint, distant galaxy as the host of the GRB. Within a year the argument over the distances to GRBs was over. GRBs occur in extremely distant galaxies. Their association with supernovae and the deaths of very massive stars also gave clues to the nature of the systems that produce GRBs.

It wasn’t too long before the race to identify optical afterglows of GRBs heated up and new satellites helped pinpoint the locations of these after glows and their host galaxies. The Swift satellite, launched in 2004, is equipped with a very sensitive gamma ray detector as well as X-ray and optical telescopes, which can be rapidly slewed to observe afterglow emissions automatically following a burst, as well as send notification to a network of telescopes on the ground for quick follow up observations.

Today, astronomers recognize two classifications of GRBs, long duration events and short duration events. Short gamma-ray bursts are likely due to merging neutron stars and not associated with supernovae. Long-duration gamma-ray bursts (GRBs) are critical in understanding the physics of GRB explosions, the impact of GRBs on their surroundings, as well as the implications of GRBs on early star formation and the history and fate of the Universe.

While X-ray afterglows are usually detected for each GRB, some still refused to give up their optical afterglow. Originally, those GRBs with X-ray but without optical afterglows were coined “dark GRBs”. The definition of “dark gamma-ray burst” has been refined, by adding a time and brightness limit, and by calculating the total output of energy of the GRB.

This lack of an optical signature could have several origins. The afterglow could have an intrinsically low luminosity. In other words, there may just be bright GRBs and faint ones. Or the optical energy could be strongly absorbed by intervening material, either locally around the GRB or along the line-of-sight through the host galaxy. Another possibility is that the light could be at such a high redshift that blanketing and absorption by the intergalactic medium would prohibit detection in the R band frequently used to make these detections.

In the new study, astronomers combined Swift data with new observations made using GROND, a dedicated GRB follow-up instrument attached to the 2.2-metre MPG/ESO telescope at La Silla in Chile. GROND is an exceptional tool for the study of GRB afterglows. It can observe a burst within minutes of an alert coming from Swift, and it has the ability to observe through seven filters simultaneously, covering 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. They then used this data to directly measure the amount of obscuring dust between the GRB and observers on Earth. Thankfully, the team has found that dark GRBs don’t require exotic explanations.

What they found is that a significant proportion of bursts are dimmed to about 60–80 percent of their 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. By proving this to be so, these astronomers have conclusively solved the puzzle of the missing optical afterglows. Dark gamma-ray bursts are simply those that have had their visible light completely stripped away before it reaches us.