Over many decades of observation gamma-ray bursts the universe has a coherent theory. All events were strictly divided into two categories: short bursts (no longer than two seconds) occurred as a result of neutron star mergers, and long bursts (from two seconds to six hours) were observed during the collapse of neutron stars. supernova. Explosive sources never crossed before, but a year ago it happened: a long burst of gamma rays originating from a source clearly outside its category.
Image source: Aaron M. Geller/Northwestern/CIERA and IT Research Computing Services
In December 2021, a team of astronomers led by scientists from Northwestern University (Chicago) discovered a long gamma-ray burst lasting 50 s. The event was numbered GRB211211A and was seen by the Fermi Space X-ray Telescope and the Neil Gerels Swift Earth Observatory Multispectral Telescope. Since long bursts of gamma rays were always recorded after a supernova explosion, an afterglow in all electromagnetic ranges remained at the collapse site of massive stars for a long time.
The prolonged afterglow, up to a week or more, made it possible to point optical, infrared and even radio telescopes at the site of the explosion and collect as much data as possible about the event. But not right now. When they looked there through the “optics”, they saw nothing at the place of the explosion. There were no supernova remnants. This meant that the long burst of gamma rays produced something different from what theory suggests.
Scientists were a little surprised and began to connect everything possible with observation, since the object exploded relatively close – at a distance of 1.1 billion light years from the Earth and it was easy to observe ( apart from interference in the form of thick clouds, which greatly interfered with this particular job).
It should be noted that short bursts of gamma rays with a duration of less than two seconds have always been recorded in binary star systems in the case of a merger of two neutron stars, a neutron star with a black hole, or, which is still a theory pure, in the case of a merger of two black holes. The masses of objects (with the possible exception of the last case) were clearly not sufficient for long-term energy release in the gamma range. The merger and subsequent explosion of such objects since 2010 is commonly called kilonovaas up to 1000 times more energy is released than in a supernova explosion.
A detailed study of the GRB211211A event in other ranges has shown that there is still an afterglow, but it is quite dim and bears signs of a kilonova explosion. In other words, a long gamma-ray burst was born under conditions that were not conducive to it and had never been observed before. This opening, at the very least, will force scientists to change their understanding of the nature of gamma-ray bursts in the Universe. New tools like the upcoming X-ray telescope to be launched next year can help. “Einstein Probe”and “James Webb”, whose infrared sensors are excellent for finding kilonovae.
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