Nothing comparable known: Mysterious gamma-ray burst observed
Two months ago, an extremely unusual astronomical event was observed with several instruments. So far, the experts have no explanation.
The gamma flash GRB 250702B.
(Image: ESO/A. Levan, A. Martin-Carrillo et al.)
Various observatories observed a gamma-ray burst like no other at the beginning of July, which was repeated several times over the course of a day. This is reported by the European Southern Observatory ESO and explains that the exact cause of the signal is a mystery. So far, it is not only the enormous length of the signal and its repetition that is inexplicable. The team also unexpectedly discovered that it did not originate from our Milky Way and was therefore much more powerful than expected. The outburst must therefore have occurred several billion light-years away. However, it is precisely this finding that could be the key to understanding it, says Antonio Martin-Carrillo, one of the astronomers involved.
Too many inconsistencies
Gamma-ray bursts (or GRBs) are among the most energetic explosions in the universe, the ESO now explains. They are caused, for example, by catastrophic collapses of massive stars. They normally last milliseconds, but minutes at most. However, the signal observed on July 2 lasted about a day. Moreover, the explosions are never repeated because the underlying event is the destruction of a celestial body. However, NASA's Fermi gamma-ray space telescope alone has detected three bursts from the source known as GRB 250702B, while others were subsequently found in data from the Chinese Einstein X-ray space telescope mission.
According to the researchers, they initially thought that the cause of the outburst must have been in the Milky Way. However, the ESO's Very Large Telescope (VLT) “fundamentally changed this view,” explains Andrew Levan, who worked on the analysis. The data contained indications that the source could be in another galaxy. The Hubble Space Telescope later confirmed the assumption. “What we discovered was even more exciting: the fact that this object is extragalactic means that it is much more powerful,” says Martin-Carrillo. The aftereffects of the explosion were analyzed using various instruments.
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If the gamma-ray burst is due to the explosion of a massive star, “this is a collapse the likes of which we have never seen before,” says Levan, assessing the scale of the event. It should have lasted a maximum of seconds. Alternatively, the outburst could have been caused by a star being torn apart by a black hole. This could explain the duration, but not other properties. For this, “an unusual star would have to be destroyed by an even more unusual black hole.” According to the preferred hypothesis, a white dwarf star was torn apart by an intermediate-mass black hole, the team writes. The research was published in the Astrophysical Journal Letter.
(mho)
