The brightest gamma-ray burst ever illuminates the Milky Way like never before

Telescopes in space and on Earth have observed the brightest gamma-ray burst on record. Data from this rare event could contribute to a better understanding of the colossal explosions that cause gamma-ray bursts. Hundreds of astronomers contributed to the research, including Andrew Levan and his group at Radboud University. He led observations with the Webb and Hubble space telescopes (Astrophysical Journal LettersMarch 28).

Gamma and X-rays from the burst provide new insight into how jet streams transport matter (jets) are accelerated and have even illuminated about 20 dust clouds in our galaxy. But one mystery remains: the remnants of the exploded star that triggered the gamma-ray burst seem to have disappeared without a trace.

GRB 221009A, as the flash is called, was first reported on October 9, 2022, when the Neil Gehrel Swift satellite detected X-rays from space. The source seemed to be in our galaxy, not far from the galactic center. However, data from the Swift and Fermi space telescopes quickly suggested it was much further away.

Observations with the X-shooter instrument on ESO’s Very Large Telescope in Chile, led by Daniele Bjørn Malesani of Radboud University, then attributed the explosion to a much more distant galaxy. ‘The explosion happened two billion light-years away, but for a burst of gamma rays, it’s in our backyard. An eruption so powerful, so close – it’s rare“Malesani said.

The fact that the gamma-ray burst came from so far away means it must have been exceptionally bright. Statistically, a gamma-ray burst as bright as GRB 221009A only occurs once in several thousand years. This may be the brightest burst of gamma rays since the dawn of human civilization.

Calculations show that the gamma-ray burst pumped about a gigawatt of energy into Earth’s upper atmosphere for a few seconds. This corresponds to the energy production of an onshore plant. ‘So many gamma and X-rays were emitted that they stimulated the earth’s ionospheresaid Erik Kuulkers, ESA project scientist for Integral, one of the space telescopes that detected the gamma-ray burst.

A vast amount of data from completely different instruments is now being brought together to understand how the original explosion happened and how the radiation interacted with other matter on its journey through space. One area that has already yielded results is how X-rays have illuminated dust clouds in the Milky Way. The radiation traveled through intergalactic space for about two billion years before entering our galaxy, the Milky Way. The radiation encountered the first dust cloud about 60,000 years ago and the last about a thousand years ago.

Each time the X-rays encountered a cloud of dust, they scattered some of the radiation, creating concentric rings that seemed to extend outward. ESA’s XMM-Newton satellite observed these rings a few days after the gamma-ray burst. The closest clouds produced the largest rings, simply because they appear larger from one vantage point.

An Italian team analyzed dust clouds and compared them with existing models. They found that one model reproduced the rings particularly well. In this model, the dust grains were mostly made of graphite, a crystalline form of carbon.

But it remains a mystery which object exploded and caused the gamma-ray burst. Levan and his colleagues used Webb to research the aftermath of the explosion, but found nothing. What this means is not entirely clear. It is possible that the star was so massive that a black hole formed immediately after the first explosion. This could have engulfed the material that would normally make up the gas cloud known as the supernova remnant.

So there is a lot of follow-up work to be done. Astronomers will continue to search for the remains of the exploded star. Among other things, they will look for traces of heavy elements such as gold, which they believe are created in such heavy explosions.

original press release