Front-row view reveals exceptional cosmic explosion

Observation challenges established theory of gamma-ray bursts in the universe


Research News


Scientists have gained the best view yet of the brightest explosions in the universe: A specialised observatory in Namibia has recorded the most energetic radiation and longest gamma-ray afterglow of a so-called gamma-ray burst (GRB) to date. The observations with the High Energy Stereoscopic System (H.E.S.S.) challenge the established idea of how gamma-rays are produced in these colossal stellar explosions which are the birth cries of black holes, as the international team reports in the journal Science.

“Gamma-ray bursts are bright X-ray and gamma-ray flashes observed in the sky, emitted by distant extragalactic sources,” explains DESY scientist Sylvia Zhu, one of the authors of the paper. “They are the biggest explosions in the universe and associated with the collapse of a rapidly rotating massive star to a black hole. A fraction of the liberated gravitational energy feeds the production of an ultrarelativistic blast wave. Their emission is divided into two distinct phases: an initial chaotic prompt phase lasting tens of seconds, followed by a long-lasting, smoothly fading afterglow phase.”

On 29 August 2019 the satellites Fermi and Swift detected a gamma-ray burst in the constellation of Eridanus. The event, catalogued as GRB 190829A according to its date of occurrence, turned out to be one of the nearest gamma-ray bursts observed so far, with a distance of about one billion lightyears. For comparison: The typical gamma-ray burst is about 20 billion lightyears away. “We were really sitting in the front row when this gamma-ray burst happened,” explains co-author Andrew Taylor from DESY. The team caught the explosion’s afterglow immediately when it became visible to the H.E.S.S. telescopes. “We could observe the afterglow for several days and to unprecedented gamma-ray energies,” reports Taylor.

The comparatively short distance to this gamma-ray burst allowed detailed measurements of the afterglow’s spectrum, which is the distribution of “colours” or photon energies of the radiation, in the very-high energy range. “We could determine GRB 190829A’s spectrum up to an energy of 3.3 tera-electronvolts, that’s about a trillion times as energetic as the photons of visible light,” explains co-author Edna Ruiz-Velasco from the Max Planck Institute for Nuclear Physics in Heidelberg. “This is what’s so exceptional about this gamma-ray burst – it happened in our cosmic backyard where the very-high-energy photons were not absorbed in collisions with background light on their way to Earth, as it happens over larger distances in the cosmos.”

The team could follow the afterglow up to three days after the initial explosion. The result came as a surprise: “Our observations revealed curious similarities between the X-ray and very-high energy gamma-ray emission of the burst’s afterglow,” reports Zhu. Established theories assume that the two emission components must be produced by separate mechanisms: the X-ray component originates from ultra-fast electrons that are deflected in the strong magnetic fields of the burst’s surroundings. This “synchrotron” process is quite similar to how particle accelerators on Earth produce bright X-rays for scientific investigations.

However, according to existing theories it seemed very unlikely that even the most powerful explosions in the universe could accelerate electrons enough to directly produce the observed very-high-energy gamma rays. This is due to a “burn-off limit”, which is determined by the balance of acceleration and cooling of particles within an accelerator. Producing very-high energy gamma-rays requires electrons with energies well beyond the burn-off limit. Instead, current theories assume that in a gamma-ray burst, fast electrons collide with synchrotron photons and thereby boost them to gamma-ray energies in a process dubbed synchrotron self-Compton.

But the observations of GRB 190829A’s afterglow now show that both components, X-ray and gamma ray, faded in sync. Also, the gamma-ray spectrum clearly matched an extrapolation of the X-ray spectrum. Together, these results are a strong indication that X-rays and very-high-energy gamma rays in this afterglow were produced by the same mechanism. “It is rather unexpected to observe such remarkably similar spectral and temporal characteristics in the X-ray and very-high energy gamma-ray energy bands, if the emission in these two energy ranges had different origins,” says co-author Dmitry Khangulyan from Rikkyo University in Tokyo. This poses a challenge for the synchrotron self-Compton origin of the very-high energy gamma-ray emission.

The far-reaching implication of this possibility highlights the need for further studies of very-high energy GRB afterglow emission. GRB 190829A is only the fourth gamma-ray burst detected from the ground. However, the earlier detected explosions occurred much farther away in the cosmos and their afterglow could only be observed for a few hours each and not to energies above 1 tera-electronvolts (TeV). “Looking to the future, the prospects for the detection of gamma-ray bursts by next-generation instruments like the Cherenkov Telescope Array that is currently being built in the Chilean Andes and on the Canary Island of La Palma look promising,” says H.E.S.S. spokesperson Stefan Wagner from Landessternwarte Heidelberg. “The general abundance of gamma-ray bursts leads us to expect that regular detections in the very-high energy band will become rather common, helping us to fully understand their physics.”


More than 230 scientists from 41 institutes in 15 countries (Namibia, South Africa, Germany, France, the UK, Ireland, Italy, Austria, the Netherlands, Poland, Sweden, Armenia, Japan, China and Australia), comprising the international H.E.S.S. collaboration, contributed to this research. H.E.S.S. is a system of five Imaging Atmospheric Cherenkov Telescopes that investigates cosmic gamma rays. The name H.E.S.S. stands for High Energy Stereoscopic System, and is also intended to pay homage to Victor Franz Hess, who received the Nobel Prize in Physics in 1936 for his discovery of cosmic radiation. H.E.S.S. is located in Namibia, near the Gamsberg mountain, an area well known for its excellent optical quality. Four H.E.S.S. telescopes went into operation in 2002/2003, the much larger fifth telescope – H.E.S.S. II – is operational since July 2012, extending the energy coverage towards lower energies and further improving sensitivity. In 2015-2016, the cameras of the first four H.E.S.S. telescopes were fully refurbished using state of the art electronics and in particular the NECTAr readout chip designed for the next big experiment in the field, the Cherenkov Telescope Array (CTA), for which the data science management centre will be hosted by DESY on its Zeuthen site.

DESY is one of the world’s leading particle accelerator centres and investigates the structure and function of matter – from the interaction of tiny elementary particles and the behaviour of novel nanomaterials and vital biomolecules to the great mysteries of the universe. The particle accelerators and detectors that DESY develops and builds at its locations in Hamburg and Zeuthen are unique research tools. They generate the most intense X-ray radiation in the world, accelerate particles to record energies and open up new windows onto the universe. DESY is a member of the Helmholtz Association, Germany’s largest scientific association, and receives its funding from the German Federal Ministry of Education and Research (BMBF) (90 per cent) and the German federal states of Hamburg and Brandenburg (10 per cent).


Revealing x-ray and gamma ray temporal and spectral similarities in the GRB 190829A afterglow; H.E.S.S. collaboration; Science, 2021; DOI: 10.1126/science.abe8560

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June 6, 2021 3:01 am

Good to see that at least in astronomy the science is definately NOT settled! There are still things we can learn.

Carlo, Monte
Reply to  Alastair Brickell
June 6, 2021 4:26 am

Unlike climastrologists, astronomers are not afraid to junk a theory when it comes up short.

Reply to  Carlo, Monte
June 6, 2021 6:44 am

Except dark matter. They’re holding on to that one despite all of its internal contradictions.

Reply to  Archer
June 6, 2021 10:06 am

Except you can openly publish papers without it, the problem is in making your replacement theory hold together with all the other observations. You know the standard drill your theory has to fit all observations not just some and frankly no one has yet devised that. So dark matter stands as the best current theory even if a bit of an ugly duckling.

Reply to  LdB
June 7, 2021 12:05 am

Dark matter theories don’t fit observations either and are contradicted regularly. Holding in to them in the face of all evidence is why alternatives aren’t able to get traction; they’re rejected because of orthodoxy and no other reason.

Reply to  Archer
June 6, 2021 2:32 pm

Quite right…maybe we could add string theory to that list too…but we can’t just blame astronomers for that one.

M Courtney
June 6, 2021 4:03 am

Hypothesis as to Gamma Ray Burst origins.
Observations makes hypothesis less likely.
New hypothesis sought.

That’s proper science , that is.

Tom Abbott
June 6, 2021 4:34 am

We need more, and bigger telescopes. The bigger they are, the more we learn.

It looks like the “international H.E.S.S. collaboration” is doing a pretty good job, and things look good for the future for them and us.

June 6, 2021 4:40 am

“The typical gamma-ray burst is about 20 billion lightyears away.”

This must be a mistake. We can’t “see” something 20 billion light years away when it would take longer than the age of the universe for the photons to reach us.

Joseph Zorzin
Reply to  ScarletMacaw
June 6, 2021 4:56 am

I’m no astronomer- but, I think it can be done- when a gamma-ray burst happened- it wasn’t that distance- but since the universe is expanding- it’s that far now.

Don Bennett
Reply to  Joseph Zorzin
June 6, 2021 5:29 am

No, the universe is estimated to be around 13.8 billion years old. The look back time-distance can only be 13.8 billion years.

Joseph Zorzin
Reply to  Don Bennett
June 6, 2021 6:42 am

yuh, the expanding space makes it confusing- but I think that though the universe is 13.8 billion years, the actual size of the visible universe is much bigger due to the expansion- which is why I thought what we can see is actually farther than 13.8 billion light years and yes, we can’t see to the beginning- not yet but it’s getting better all the time- I’ll pursue this further- I do really like astronomy- mind blowing- especially that most of the universe is dark matter or dark energy- what amazing things will we discover once we learn more about the dark stuff?

Joseph Zorzin
Reply to  Joseph Zorzin
June 6, 2021 6:45 am

Wikipedia: “The proper distance—the distance as would be measured at a specific time, including the present—between Earth and the edge of the observable universe is 46 billion light-years[54] (14 billion parsecs),[55] making the diameter of the observable universe about 93 billion light-years (28 billion parsecs).[54] The distance the light from the edge of the observable universe has travelled is very close to the age of the universe times the speed of light, 13.8 billion light-years (4.2×109 pc), but this does not represent the distance at any given time because the edge of the observable universe and the Earth have since moved further apart.”

oeman 50
Reply to  Joseph Zorzin
June 6, 2021 8:04 am

How is that a “front row seat?” I think it is million to billion typo.

Tom Abbott
Reply to  Joseph Zorzin
June 6, 2021 8:57 am

“28 billion parsecs”

Why is the term “parsecs” even used anymore? I don’t see it as an improvement over the lightyear on measuring distance.

Of course, the hero in the Star Wars movie, Han Solo, thinks parsecs are a measure of speed.

Joseph Zorzin
Reply to  Tom Abbott
June 6, 2021 9:03 am

It might make sense for distances that are only a few parsecs or some portion of a parsec but once you get into billions of parsecs- seems you might as well use light years.

Reply to  Joseph Zorzin
June 6, 2021 12:26 pm

Use meters or centimeters. Your choice.

Reply to  Tom Abbott
June 6, 2021 10:44 am

Astronomical distances assume that speed of light is constant wherever you have to be, I have some doubts about that, in vicinity of large masses light takes curved path. For anything moving on a curved path its velocity vector is continually changing, and thus it has acceleration (which can be positive or negative, i.e. speeding or slowing down).
Einstein said speed of light is constant, then contradicted himself to predict that light would bend in presence of large mass, so you have it!

Joseph Zorzin
Reply to  Vuk
June 6, 2021 1:23 pm

Light doesn’t bend- it’s the space that has bent and light must follow it. No contradiction.

Reply to  Joseph Zorzin
June 6, 2021 1:37 pm

You think what you like, I prefer to think that there is no BENT space but there may be a quantum gravity (attracting everything including photons) as per Rodger Penrose.

Joseph Zorzin
Reply to  Vuk
June 6, 2021 1:49 pm

I attached a photo which proves space can bend. 🙂

IMG_20190420_164913_00_022_2019-04-20_17-51-58_screenshot magnolia in bloom on tiny planet.jpg
Tom Abbott
Reply to  Joseph Zorzin
June 7, 2021 2:32 am

Is that you in the picture? 🙂

Joseph Zorzin
Reply to  Tom Abbott
June 7, 2021 3:07 am

Yes- I have thousands of such photos and videos taken with a 360 degree video camera.

David Blenkinsop
Reply to  Joseph Zorzin
June 7, 2021 10:46 am

Actually, the spherical area covered in principle here, is maximum, four square radians (for a whole sphere), or, for the stereographic projection, likely something close to just two square radians (half sphere). If my math is correct, that would be 64,800 square degrees covered, not 360 really.

Aside from me making a great ol’ nitpick like that, it’s a cool picture for sure.

David Blenkinsop
Reply to  David Blenkinsop
June 7, 2021 11:25 am

Oops, I missed specifying a factor of ‘pi’ there. It’s 4 times ‘pi’ square radians for a sphere, then 2 times ‘pi’ square radians, if the projection photo really only accounts for a half sphere of overall viewing area. In square degrees, this should translate to 64,800 times ‘pi’ square degrees. It seemed a bit simpler when I mispoke it, sheesh.

Joseph Zorzin
Reply to  David Blenkinsop
June 7, 2021 11:32 am

To learn about 360 videos, check out Ben Claremont’s channel at and another, “ScJo in 360” at I’ve got some videos made with this camera – along with some videos I made with an old GoPro and a few with a very old Canon camcorder at:

10 years to record the Earth roasting as promised by the Climatista priesthood and prophets.

Tom Abbott
Reply to  Vuk
June 7, 2021 2:30 am

I think some of our assumptions are inevitably going to change about how the universe works.

I see where some people are thinking the graviton may not be massless. Which would affect the expansion of the universe.

They used to think the neutrino did not have any mass, but they found out differently.

Joseph Zorzin
Reply to  Tom Abbott
June 7, 2021 9:50 am

If you like astronomy- I suggest subscribing to Astronomy Magazine- though you can read much of it on their web site.

astronomy is a fantastic science

Tom Abbott
Reply to  Joseph Zorzin
June 8, 2021 3:42 am

“If you like astronomy- I suggest subscribing to Astronomy Magazine”

I do. Great magazine. Except when the Editor decides to expound on Human-caused Climate Change. Although he has only done that about two times. That’s two times too many, as far as I’m concerned. He should stick to astronomy. A subject he knows something about.

Reply to  Vuk
June 7, 2021 7:39 am

I know I am quibbling here, but what is commonly called the speed of light is a maximum speed rather than a constant. That maximum speed is in a vacuum; light can indeed be less than the magic 300,000 m/s while traveling through other non-opaque media. 

Joseph Zorzin
Reply to  PaulH
June 7, 2021 9:46 am
Reply to  Joseph Zorzin
June 7, 2021 2:41 pm

Oh! Now that is cool. 🙂

Reply to  PaulH
June 7, 2021 9:39 pm

That’s 300,000 km/sec, of course.

Reply to  Joseph Zorzin
June 6, 2021 12:25 pm

This seems to say that the expansion rate is much greater than the speed of light. Light has traveled for 13.8 billion years since the universe supposedly began. The “edge of the universe” has traveled 3.3 times as far as light has had time to travel. What is my error?

Joseph Zorzin
Reply to  AndyHce
June 6, 2021 1:20 pm

The edge didn’t travel anywhere- nor does anything else- it’s space that is expanding so things move apart. And yes, the farther you go- the faster everything is “moving” or appears to move- and way faster than the speed of light- or appears to. Just the way it is. The expansion rate isn’t faster than the speed of light- it’s accumulative- it adds up- the farther from here- the more it has added up. And since the rate of expansion is accelerating- at some future point, from here, we (if anyone is around) won’t see any galaxies beyond the Milky Way as they’ll have moved beyond what we can see. Amazing stuff. I’m sure I’m not explaining this well but it’s basically correct.

Reply to  AndyHce
June 6, 2021 8:59 pm

The speed of light, c, is limited within our universe. However, the universe itself can & does expand faster than c.

Joseph Zorzin
Reply to  anthropic
June 7, 2021 10:01 am

The rate of expansion is actually rather slow- but it’s accumulative- it’s a rate of expansion per unit of distance- the greater the distance, any 2 objects are growing apart faster. According to a Google search, “This means that for every megaparsec — 3.3 million light years, or 3 billion trillion kilometers — from Earth, the universe is expanding an extra 73.3 ±2.5 kilometers per second.” And since the consensus is that the universe is infinite- there are galaxies sufficiently far away from us that the distance between us is growing at many times the speed of light- though none are actually moving at all relative to space- though they may be moving in all sorts of directions compared to other galaxies that are relatively close. Or something like that- I’m no scientist- I just eat up this stuff like candy. Took the standard basic astronomy course in college back in the late ’60s and reading the subject ever since- lots of books on relativity and string theory and Astronomy Magazine. Then there was that acid trip watching “2001 Space Odyssey” at a drive in back in ’69. 🙂

Tom Abbott
Reply to  Joseph Zorzin
June 8, 2021 3:48 am

“Then there was that acid trip watching “2001 Space Odyssey” at a drive in back in ’69.”

That’s where I first saw that movie, at the Drive In.

Reply to  Joseph Zorzin
June 7, 2021 9:34 am

yeah but technically that GRB has burned out over 13 billion years ago so it is not proper to say that it is now 30 billion LY away (because now is not then)… the proper thing in my mind to put the time in synch is to move the Milky Way back in time to when the event occurred in which case perhaps it was perhaps even less than 1 billion LY away back then (however maybe the Milky Way as we know it did not even exist then but the point in space certainly could be extrapolated backward)

Reply to  Joseph Zorzin
June 6, 2021 9:08 am

Astonerii nailed it. Astronomers don’t measure distance to where it might be now. The 20 billion light years is the distance it appears to be.

I agree with oeman 50. The mistake is probably a million to billion error.

Reply to  ScarletMacaw
June 6, 2021 10:15 am

Yeah I noticed that, too. Should be more like 10 I’m thinking?

mike macray
Reply to  ScarletMacaw
June 7, 2021 8:44 am

That had me puzzled too! The ‘year’ has only been around for 4 and a half billion years or so since mother earth stared circling the sun.
Maybe time is a variable after all.

June 6, 2021 6:12 am

I am confused. 1 Trillion equals 10^12. 1 Terra equals ie 1 times So how can “We could determine GRB 190829A’s spectrum up to an energy of 3.3 tera-electronvolts, that’s about a trillion times as energetic as the photons of visible light,” be correct.

June 6, 2021 6:29 am

So what are the odds that it simply was the fleet disembarking for maneuvers?

June 6, 2021 8:14 am

The typical gamma-ray burst is about 20 billion lightyears away.”

Let me calculate this up… Travels 1 light year per year. 13.8 billion years since the “big bang”.

Hmm, and people wonder why I do not trust “scientists”.

I am sure there are all kinds of explanations, but the truth is that light only travels at the speed of light. Which is said to be constant. Thus, at the time that this event happened, it happened at a distance equal to the speed of light times the time it took to get here.

Maybe they are in fact further away today, but that does not change the reality of exactly how far away these events APPEAR to have happened with respect to us.

Reply to  astonerii
June 6, 2021 11:55 am

There are lot of errors, press release, translation from German, in Europe billion is not same as in the USA.
1 000 000 000 000= European billion (equivalent to a million million)
1 000 000 000= American billion (equivalent to a thousand million)

Reply to  astonerii
June 6, 2021 12:29 pm

The “speed of light” is the upper limit.

June 6, 2021 8:23 am

They by chance made an amazing observation and will make more with the next generation of instruments. And reported it without an axe to grind. Comments on what can be seen with the expanding universe, fun to read.

June 6, 2021 12:00 pm

“The radius of the observable universe is therefore estimated to be about 46.5 billion light-years and its diameter about 28.5 gigaparsecs…..
 …. the current comoving distance—proper distance, which takes into account that the universe has expanded since the light was emitted”

Leonard Weinstein
June 6, 2021 12:04 pm

Either billion means something different than 10^9, or a mistake was made. The quote was the average burst occurs 20 billion LY away, while the radius of the observable universe is <15 billion LY.

Reply to  Leonard Weinstein
June 6, 2021 12:44 pm

Billion in Europe is 1 000 000 000 000 i.e. 10^12
The radius of the observable universe is estimated to be about 46.5 billion (american 10^9 ) light-years which takes into account that the universe has expanded since the light was emitted, and apparently space expansion may be as fast as speed of light (or even faster, but that light will never reach us). Mind boggles.

Tom Abbott
Reply to  Vuk
June 7, 2021 2:38 am

“Mind boggles”

Yes! 🙂

June 6, 2021 2:07 pm

further above I mentioned quantum gravity, which may or may not exist. An experiment has been proposed to confirm hypothesiscomment image
For those interested more can be found here:

Reply to  Vuk
June 6, 2021 2:22 pm

if you prefer to listen there is a ‘podcast’ (digital audio file) at the top of the article.

June 7, 2021 8:08 pm

More than 230 scientists from 41 institutes in 15 countries”

Uh-oh. That’s an awful lot of authors for one series of observations.

June 7, 2021 8:09 pm

I do love reading these posts; I always come away with a new appreciation of the universe.

But I never can help chuckling at “front row seat” and “in our own backyard.” Great excitement over an event that happened just as our remote ancestors were literally inventing sex for the first time (unlike every teenager believes they do).

Here’s to hoping that we never have a “front row seat” “in our own backyard” as defined by mere mortals for such an event.

Michael S. Kelly
June 8, 2021 1:22 am

 The typical gamma-ray burst is about 20 billion lightyears away.” I thought the end of the universe was 13.5 billion light years away, so how is this possible?

The answer to all other questions is still “42”.

June 8, 2021 4:20 am
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