A massive gamma-ray burst more than a billion light-years from Earth is the largest explosion in the Universe ever captured on camera by astronomers.
The explosive event marked the death of a star and the beginning of its transformation into a black hole, according to experts at Germany’s Electron Synchrotron in Hamburg.
This was a massive gamma-ray burst, consisting of a combination of bright X-ray and gamma-ray bursts seen in the sky, emitted from distant extragalactic sources.
It was detected by Fermi and Swift telescopes in space, with support from the Earth-based High Energy Stereoscopic System (HESS) telescope in Namibia.
Artist’s impression of a relativistic beam of a gamma ray burst (GRB), breaking out of a collapsing star and emitting highly energetic photons
WHAT CAUSED THE EXPLOSIVE CRACK?
In a distant galaxy, a massive, dying star collapses, forming a neutron star or black hole.
Two vertical relativistic plasma jets are formed, which break through the envelope of the star.
The star eventually explodes in a supernova. The plasma jets plow through the surrounding gas and collect electrons.
These electrons are deflected by magnetic fields in the jet and accelerated by the shock wave.
With each deflection, the fast electrons then emit light particles in the range of X-rays and gamma rays.
This light is called synchrotron radiation and is focused in the direction of the plasma beam by relativistic effects.
Looking straight into the jet from the front reveals the event as a gamma-ray burst.
About 900 million years later, the radiation from this gamma-ray burst reaches Earth and is recorded by satellites and telescopes.
Despite being a billion light-years from Earth, this is considered our “cosmic backyard,” coming from the constellation Eridanus.
It’s the most energetic radiation and with the longest gamma-ray afterglow of any gamma-ray burst discovered to date, says the German team that saw it.
Previous gamma-ray bursts were an average of 20 billion light-years away.
The burst, dubbed GRB 190829A, was first detected on August 29, 2019.
“The observations with HESS challenge the established idea of how gamma rays are produced in these colossal stellar explosions that are the birth cries of black holes,” the team said.
dr. Andrew Taylor of Germany’s Electron Synchrotron (DESY), co-author of the book, said they were “front row” when the gamma-ray burst happened.
“We could observe the afterglow for days and up to unprecedented gamma-ray energies,” explained the DESY scientist.
The relatively short distance to this gamma-ray burst allowed detailed measurements of the afterglow spectrum, that is, the distribution of photon energies of the radiation in a very high energy range.
Co-author Edna Ruiz-Velasco, a PhD student from the Max Planck Institute for Nuclear Physics in Germany, was also involved in the research.
She said they could determine the spectrum to 3.3 tera-electron volts, or a trillion times more energetic than photons in visible light.
“This is what’s so extraordinary about this gamma-ray burst — it happened in our cosmic backyard,” Ruiz-Velasco explained.
‘The very high-energy photons were not absorbed in collisions with background light on their way to Earth, as happens over greater distances in the cosmos.’
The team was able to track GRB 190829A’s afterglow, the fourth gamma-ray burst detected from the ground, until three days after the first explosion.
However, the previously detected explosions occurred much further away and their afterglow could be observed for only a few hours each and at much lower energies.
DESY scientist Sylvia Zhu, one of the authors of the paper, said these eruptions are the largest explosions in the universe, caused by the collapse of a rapidly rotating star.
X-rays from the gamma-ray burst were detected by NASA’s Swift satellite orbiting Earth. High energy gamma rays entered the atmosphere and caused air showers detected by the HESS telescopes from the ground (artist’s impression)
WHAT ARE GAMMA RAY BURSTS?
Gamma ray bursts (GRBs), energetic beams of gamma rays emanating from black holes, can be created in two different ways, resulting in long or short GRBs.
They arose from some of the most violent deaths in the universe.
Long GRBs last about a minute and scientists think they are produced by supernovae: when the core of a massive star collapses and becomes a black hole.
Short GRBs last a second and are produced when two neutron stars merge.
These stars are in their final moments before turning into black holes, when a fraction of the gravitational energy released fuels the production of an ultra-relativistic blast wave — detected as a gamma-ray burst.
“Their emission is divided into two distinct phases: an initial chaotic prompt phase lasting tens of seconds, followed by a prolonged, gradually fading afterglow phase,” explains Zhu.
The team was able to monitor the afterglow for up to three days after the initial explosion. The result came as a surprise, as observations revealed curious similarities between the X-rays and the highly energetic gamma rays of the afterglow.
Established theories assume that the two emission components must be produced by a separate mechanism, similar to how particle accelerators on Earth produce bright X-rays for scientific research.
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 between acceleration and cooling of particles within an accelerator on Earth.
But the observations of GRB 190829A’s afterglow now show that both components, X-rays and gamma rays, faded synchronously. Also, the gamma-ray spectrum clearly corresponded to an extrapolation of the X-ray spectrum.
Together, these results strongly indicate that X-rays and high-energy gamma rays in this afterglow were produced by the same mechanism.
Artist’s impression of very high energy photons from a gamma-ray burst entering the Earth’s atmosphere and causing air showers captured by the telescopes of the High Energy Stereoscopic System (HESS) in Namibia.
“It is quite unexpected to see such remarkably similar spectral and temporal features in the energy bands of very high energy X-rays and gamma rays, if the emission in these two energy regions had different origins,” said co-author Dmitry Khangulyan of Rikkyo University. in Tokyo.
The far-reaching implication of this possibility highlights the need for further research into very high energy GRB afterglow emission.
HESS spokesman Stefan Wagner said the prospects for the detection of gamma-ray bursts by next-generation instruments look promising.
This includes the Cherenkov Telescope Array currently under construction in the Chilean Andes and on the Canary Island of La Palma.
“The general abundance of gamma-ray bursts makes us expect that regular detections in the very high energy band will become quite common, which will help us fully understand their physics,” he said.
The article was published in the magazine Science.
SUPERNOVAE RISES WHEN A GIANT STAR EXPLODES
A supernova occurs when a star explodes and blasts debris and particles into space.
A supernova only burns for a short time, but can tell scientists a lot about how the universe came to be.
One type of supernova has shown scientists that we live in an expanding universe, one that is growing faster and faster.
Scientists have also determined that supernovae play a key role in the distribution of elements throughout the universe.
In 1987, astronomers spotted a ‘titanic supernova’ in a nearby galaxy that sparkled with the power of more than 100 million suns (pictured)
Two types of supernovae are known.
The first type occurs in binary star systems when one of the two stars, a carbon-oxygen white dwarf, steals matter from its companion star.
Eventually, the white dwarf accumulates too much matter, causing the star to explode, resulting in a supernova.
The second type of supernova occurs at the end of the life of a single star.
When the core of the star runs out, some of its mass flows to the core.
Eventually, the core is so heavy that it can’t bear its own gravity and the core collapses, resulting in another giant explosion.
Many elements found on Earth are created in the cores of stars, and these elements travel onward to form new stars, planets, and everything else in the universe.