Cosmic rays: The brightest gamma-ray burst of all time and its mystery

Science cosmic rays

The brightest gamma ray burst of all time and its secret

HANDOUT - Illustration of the brightest GRB 221009A.  Credit: Image by IHEP/HXMT&GECAM Team ATTENTION: Free for editorial use only in connection with reporting on the study if the credit is given.  Photo: Image by IHEP/HXMT&GECAM Team

Illustration to GRB 221009A, the lightning bolt’s official name

Source: Image by IHEP/HXMT&GECAM Team

A very rare event: In October 2022, massive gamma rays hit the earth. The afterglow can still be seen. Astrophysicists are enthusiastic and explore the origin – and whether a black hole was involved.

V1.9 billion years ago there was a special event in a galaxy far, far away. The high-energy gamma rays released in the process hit the earth a little later. More precisely on October 9, 2022. It was the strongest gamma-ray burst ever recorded. Almost simultaneously, the two space telescopes Fermi and Swift automatically triggered the alarm.

Astronomers around the world began pointing their telescopes at the origin of the cosmic cataclysm. In the Astrophysical Journal Letters several teams are now presenting the results of their observations: the brightest gamma-ray burst of all time remains a mystery, there was no trace of an exploded star.

This gamma-ray burst was strange from the start, recalls Maia Willems from the Swift team: “It was much too bright, so I initially thought it had to be something else.” But since Fermi and other observatories had also registered the radiation burst, it was It quickly became clear: GRB 221009A – as it is officially called – was the strongest gamma-ray burst ever recorded.

HANDOUT - Illustration of the Insight-HXMT and GECAM-C observations of the brightest gamma-ray burst (GRB 221009A).  Credit: Image by IHEP/HXMT&GECAM Team ATTENTION: Free for editorial use only in connection with reporting on the study if the credit is given.  Photo: Image by IHEP/HXMT&GECAM Team

Illustration of the Insight-HXMT and GECAM-C space satellites

Source: Image by IHEP/HXMT&GECAM Team

HANDOUT - XMM-Newton images recorded 20 dust rings, 19 of which are shown here in arbitrary colours.  The image merges observations made two and five days after GRB 221009A erupted.  Dark stripes indicate gaps between the detectors.  A detailed analysis shows that the widest ring visible here, comparable to the apparent size of a full moon, came from dust clouds located about 1300 light-years away.  The innermost ring arose from dust at a distance of 61,000 light-years - on the other side of our galaxy.  GRB221009A is only the seventh gamma-ray burst to display X-ray rings, and it triples the number previously seen around one.  Credit: ESA/XMM-Newton/M.  Rigoselli (INAF) ATTENTION: Free for editorial use only in connection with reporting on the study if the credit is given.  Photo: ESA/XMM-Newton/M.  Rigoselli (INAF)

Gamma rays with X-ray rings: observations made two and five days after the outburst of GRB 221009A

Source: ESA/XMM-Newton/M. Rigoselli (INAF)

Due to the enormous brightness, the researchers initially suspected that it was an explosion within our Milky Way, perhaps only a few tens of thousands of light-years away.

But measurements from the various astronomical instruments quickly showed that the source of the gamma-ray burst was much further away, in a galaxy some 1.9 billion light-years away. And so it was clear: The triggering explosion had to be powerful so that the flash could light up so brightly from this distance in the earthly sky.

In addition, the gamma radiation must have been tightly bundled towards Earth. This makes GRB 221009A an extremely rare event – Alicia Rouco Escorial from the European space agency Esa estimates that such a strong gamma-ray burst could only hit Earth every few thousand years: “So we were extremely lucky to experience such an event.”

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Two neutron stars with gamma ray burst

Astrophysicists suspect two different causes of gamma-ray bursts. Brief flashes lasting less than two seconds are triggered by the collapse of an old, very massive star. This creates a black hole. On the other hand, longer flashes occur when two neutron stars or black holes merge, which also triggers gravitational waves.

The gamma-ray burst of October 9, 2022 belonged to the first category – it was brief and no gravitational waves were detected.

In both cases, part of the explosion energy shoots out into space in the form of gamma rays, among other things. Only when such a beam of radiation hits the earth do astronomers register a gamma-ray burst and thus receive information about the distant cosmic catastrophe. Calculations show that GRB 221009A transported a total of one gigawatt of energy into the upper atmosphere – briefly lighting up the ionosphere.

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Computer graphics from NASA's COSI gamma-ray telescope

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Similarly, the shower of gamma rays also lit up twenty dust clouds within the Milky Way – an opportunity for astrophysicists to study their nature. As observations with the European XMM-Newton space telescope show, the dust in these clouds consists mainly of graphite.

Now, half a year after the event, the astronomers are still regularly observing the region of origin of the gamma-ray burst. Because the afterglow of the explosion is still visible, and probably for a long time due to the strength of the flash.

“We will see the afterglow for years to come,” explains Volodymyr Savchenko of the University of Geneva. By observing the afterglow, the researchers hope to be able to track down the cause of the explosion.

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This image released by NASA on Tuesday, July 12, 2022, shows the edge of a nearby, young, star-forming region NGC 3324 in the Carina Nebula.  Captured in infrared light by the Near-Infrared Camera (NIRCam) on the James Webb Space Telescope, this image reveals previously obscured areas of star birth, according to NASA.  (NASA, ESA, CSA, and STScI via AP)

That remains a mystery for the time being. Andrew Levan from Radbound University in the Netherlands and his colleagues report on their search for the remains of an exploded star with the Hubble and Webb Space Telescopes. They didn’t find anything, “and that’s crazy,” says Levan, “we just don’t know what it means.” One possible explanation would be that a black hole formed so quickly that any remnants of the blast were instantly engulfed.

The researchers now want to look specifically for heavy elements such as gold in the area, which can only occur in such explosions. GRB 221009 will keep scientists busy for a while.

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