Best View Yet of Exceptional Cosmic Explosion – Challenges Established Theory of Gamma-Ray Bursts in the Universe

Relativistic Jet of a Gamma-Ray Burst

Artist’s impression of a relativistic jet of a gamma-ray burst (GRB), breaking out of a collapsing star, and emitting very-high-energy photons. Credit: DESY, Science Communication Lab

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

Scientists have gained the best view yet of the brightest explosions in the universe: A specialized 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 August 29, 2019, the satellites Fermi and Swift detected a gamma-ray burst in the constellation of Eridanus. The event, cataloged 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 “colors” 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.”

Very-High-Energy Photons From a Gamma-Ray Burst

Artist’s impression of very-high-energy photons from a gamma-ray burst entering Earths’ atmosphere and initiating air showers that are being recorded by the telescopes of the High Energy Stereoscopic System (H.E.S.S.) in Namibia. Credit: DESY, Science Communication Lab

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.

X-rays From Gamma-Ray Burst Detected by NASA's Swift Satellite

X-rays from the gamma-ray burst were detected by NASA’s Swift satellite in Earth’s orbit. Very-high-energy gamma rays entered the atmosphere and initiated air showers that were detected by the H.E.S.S. telescopes from the ground (artist’s impression). Credit: DESY, Science Communication Lab

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.”

Reference: “Revealing x-ray and gamma ray temporal and spectral similarities in the GRB 190829A afterglow” by H.E.S.S. collaboration, 3 June 2021, Science.
DOI: 10.1126/science.abe8560

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 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 center will be hosted by DESY on its Zeuthen site.

DESY is one of the world’s leading particle accelerator centers and investigates the structure and function of matter — from the interaction of tiny elementary particles and the behavior 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 percent) and the German federal states of Hamburg and Brandenburg (10 percent).

21 Comments on "Best View Yet of Exceptional Cosmic Explosion – Challenges Established Theory of Gamma-Ray Bursts in the Universe"

  1. Marin Tomuța | June 3, 2021 at 5:12 pm | Reply

    Animations, fakes, deepfakes, cgi, artist impressions…..this is what is replacing actual observations?
    Scientists are discrediting themselves in my view.

    • Torbjörn Larsson | June 7, 2021 at 5:02 am | Reply

      No, it isn’t replacing observations.

      What you are looking at are meant as helpful illustrations for your sake.

  2. Marin Tomuța | June 3, 2021 at 5:14 pm | Reply

    Animations, fakes, deepfakes, cgi, artist impressions…..this is what is replacing actual observations?
    Scientists are discrediting themselves in my view.
    Not all news have to have images.

  3. Juan E Jimenez | June 3, 2021 at 5:35 pm | Reply

    “The typical gamma-ray burst is about 20 billion lightyears away.” Which means the so-called “estimates” of the age of the universe are all completely wrong.

    • Torbjörn Larsson | June 7, 2021 at 5:04 am | Reply

      Are you suggesting a linear expansion, so radius of observable universe would be proportional to time?

      That never happens in practice, for instance if the universe content was only matter a galaxy on a shell outside closer galaxies would recede as a throw parabola due to gravity from the matter content.

      Now as dark energy dominates the expansion function approaches an exponential [ ].

  4. Stephen Osiobe. | June 3, 2021 at 8:27 pm | Reply

    Quite interesting and most fascinating. I shear the view that using artistic impressions to illustrate this once in a life observation detracts from the reality of science as a fact based enterprise. Photo shots of the event are much better illustrations. Good job.please keep it on.

    • Torbjörn Larsson | June 7, 2021 at 5:07 am | Reply

      X-ray detectors are not cameras.

      You can puzzle together an image for illustrative purposes later. In most cases they use illustrators that know a bit about the motive. But that has nothing (or very little) to do with the science.

  5. Those opposing use of artistic impressions should take note this is being done by the popular press, not by the scientists; if you want more facts and less artistry, go and read the respective scientific paper (it’s linkef in the article, look for “DOI: 10.1126/science.abe8560”)

    • Torbjörn Larsson | June 7, 2021 at 5:09 am | Reply

      Oh, scientists may help out as well! Better press coverage means a lot for them and their universities, which press offices are often the source of the illustrations.

      Still, meant to help spread the science, not (much) part of the work underlying it.

  6. @JuanJimenez “‘The typical gamma-ray burst is about 20 billion lightyears away.’ Which means the so-called ‘estimates’ of the age of the universe are all completely wrong”

    It does not; instead, it means that the universe has been expanding in an accelerated manner during the time these gamma rays were on their way to us. As an analogy, it’s the same as you running many miles on your treadmill while moving only a few feet in the gym.

  7. Sorry, the typical gamma ray burst cant be 20B lightyears away. The furthest on record was 13B light years away.

  8. Mike Pollock | June 4, 2021 at 5:51 am | Reply

    This was a black hole getting impacted by a meteor. This turned the once single mass of quark plasma into a trillion various sized black holes. Their new sizes all cool much faster based on the fact they are much smaller. The bigger pieces would still be releasing gamma rays while the smaller ones would release less powerful energy in x-rays. This is why there is an even mix of the two radiations and why they cooled down at relatively the same time.

  9. Bibhutibhusan Patel | June 4, 2021 at 7:03 am | Reply

    Well.all these are bodies created and placed as randum as possible,are part of some galaxy.Sòmetimes new bòdies can be dìscovered to have more advanced form and function belonging to same category having necessary to be discrìbed by laws of hìgher order.Ofen these change structural syntax.

  10. BibhutibhusanPatel | June 4, 2021 at 7:11 am | Reply

    Though article lost proper scientific connection,in real cases discoveries òf higher orďer are possible.

  11. Funny how I told this magazine exactly why gamma rays and x rays were being emitted at the same time and it gets erased. No spam, no links, just the truth. No wonder science has been in ruin for one hundred years. One day, something be will discover the theory of everything. How will it happen? Who will it be? Of course, it won’t make sense at first but, as the laws of our universe are applied to the theory, it will stand out as right. One day, one day.

    • Torbjörn Larsson | June 7, 2021 at 5:17 am | Reply

      Funny how conspiracy theories – and lack of evidence combined with claims against porovided evidence rank high on the crackpot index [ ].

      “40 points for claiming that the “scientific establishment” is engaged in a “conspiracy” to prevent your work from gaining its well-deserved fame, or suchlike.”

  12. WOW mike you see some ridiculous comments here but your meteor hitting a black hole idea has to be right up there. Science isn’t just making things up. Maybe you should stick to Thomas Aquinas or something along those lines.

  13. woops sorry that was “quark plasma”! ……LOL…

Leave a comment

Email address is optional. If provided, your email will not be published or shared.