Scientists at Northwestern University in Evanston, Illinois, USA have discovered a long burst of gamma rays that has an unknown origin and contradicts what humanity knows about this phenomenon.
Scientists have been studying gamma-ray bursts in the universe for several decades, and so it seemed that almost everything was known about them. Gamma-ray bursts are thought to fall into two groups: short bursts—lasting from 10 milliseconds to 2 seconds—caused by the merger of two neutron stars, a black hole and a neutron star, or two black holes; but this is only a theory, in practice no one has ever seen it before, and long outbursts—lasting from 2 seconds to 6 hours—that occur during a supernova explosion when the rapidly rotating core of a massive star collapses.
The sources of these two types of bursts have never been crossed before. But in December 2021, scientists saw a 50-second burst of gamma rays that was not associated with a supernova. This event, which was numbered GRB211211A, occurred 1.1 billion light-years from Earth. It was seen using the Fermi Gamma-ray Space Telescope and the multispectral telescope at the Neil Gehrels Swift Observatory.
Because long-lasting gamma-ray bursts always occur after a supernova explodes, this event has a long-lasting afterglow that can be found in all electromagnetic belts and last for about a week or even more. Scientists could point optical, infrared, and even radio telescopes at the site of the explosion and collect data on what happened. But this time, when scientists looked at the site of the gamma-ray burst with "optics," they didn't see supernova remnants or anything else. And this means that the cause of the burst of gamma rays is not at all the explosion of a supernova, as it was commonly assumed.
But even with neutron stars and/or black holes, this phenomenon is quite difficult to associate because their mass is usually not enough for long-term emission of energy in the gamma range. Perhaps an exception could be the merger of two black holes; but, as already mentioned, no one has ever observed such a thing.
Either way, the appearance of a long burst of gamma rays under unusual conditions will force scientists to change their understanding of the nature of this phenomenon. Both the James Webb Space Telescope, which has infrared sensors perfectly suited for the search for kilonovae, and the Einstein Probe X-ray telescope, which is scheduled to launch in 2023, will help them in their research in this domain.