After decades of observations of gamma-ray bursts in the universe, a neat theory has been developed. All events were strictly divided into two categories: short bursts (no longer than two seconds) occurred due to the merger of neutron stars, and long bursts (from two seconds to six hours) were observed during the collapse of supernovae. The sources of the explosions have never intersected before, but a year ago they passed: a long burst of gamma rays from a source clearly outside its category.

In December 2021, a group of astronomers led by scientists from Northwestern University (Chicago) detected a long burst of gamma rays lasting 50 seconds. The event received the number GRB211211A and was seen by the Fermi Space X-ray Telescope and the Earth-based Neil Gehrels Swift Multispectral Telescope. Since long gamma-ray bursts are always recorded after a supernova explosion, the afterglow of collapsing massive stars long dominated all electromagnetic ranges.

The long — lasting a week or more — flare made it possible to point optical, infrared, and even radio telescopes to the location of the blast and collect as much data about the event as possible. But not this time. When they looked there with optics, they couldn’t see anything where the explosion was. There were no supernova remnants there. This meant that the long gamma-ray burst was produced by something different from what theory predicted.

Scientists were somewhat puzzled and began to attribute everything possible to observation, because the object exploded relatively close – 1.1 billion light-years from Earth, and it was easy to observe it (except for obstacles in the form of thick clouds), which greatly hindered this work.

It should be noted that short gamma-ray bursts lasting less than two seconds have always been recorded in binary star systems, as is the merging of two neutron stars, or the merging of a neutron star with a black hole, which is still pure theory. , if two black holes merge. The mass of the objects (except for the possible last case) was not sufficient for long-term energy emission in the gamma range. The merger and subsequent explosion of such objects has been called kilonova since 2010, as up to 1000 times more energy is released than during a supernova explosion.

A detailed examination of the GRB211211A event in other bands showed that the post-sunset glow was still there, but rather faint, and showed signs of a kilonova explosion. In other words, the long gamma-ray burst was born in conditions never before observed. At the very least, this discovery will force scientists to change their understanding of the nature of gamma-ray bursts in the universe. New tools like the Einstein Probe X-ray telescope, set to launch next year, and James Webb, whose infrared sensors are perfect for looking for kilomons, could help. Source