Astrophysicists have long believed that only massive star collapses could generate long gamma-ray bursts. Now, a new finding shows that long gamma-ray bursts can be generated by neutron star mergers.
Gamma ray bursts are the brightest and most energetic explosions occurring in the universe since the Big Bang. These are divided into two classes – short (2 seconds or less) or long (above 2 seconds). Scientists have generally held the view that these two types have very different origins. The new finding disproves this.
The evidence for the new assumption is from what is known as a ‘kilonova’, an event that is only generated from neutron star mergers, is followed a long gamma-ray burst. This new information is not only of interest in terms of astronomical events for it provides new clues in the search for heavy elements.
Kilonovae produce gamma-ray bursts and strong electromagnetic radiation due to the radioactive decay of heavy r-process nuclei. The level of brightness produced from the event is 1000 times that of a classical nova.
There is a difference between a supernova and a kilonova. This is that kilonovae are formed when two neutron stars collide whereas a supernova occurs when either a white dwarf that is 1.44 (or greater) solar masses or a star that is 8 (or greater) solar masses explodes, producing a neutron star.
The research arose after Northwestern University scientists detected a 50-second-long gamma-ray burst in December 2021 (named GRB211211A and located some 1.1 billion light-years away in a galaxy named SDSS J140910.47+275320.8). The team began searching for the long GRB’s afterglow, which is an incredibly luminous and fast-fading burst of light that often precedes a supernova.
However, contrary to expectations, the scientists uncovered evidence of a kilonova. This in itself is a rare event. The kilonova recorded a burst of similar luminosity, duration and colour to that which accompanies previously described gravitational wave detected binary neutron star mergers.
One of the lead scientists. Jillian Rastinejad states: “This event looks unlike anything else we have seen before from a long gamma-ray burst…This event represents an exciting paradigm shift for gamma-ray burst astronomy.”
The consequence of the discover may later how astrophysicists approach the search for heavy elements, such as platinum and gold, and with this offer new clues to the formation of the cosmos.
The research has been published in the science journal Nature. The paper is titled “A kilonova following a long-duration gamma-ray burst at 350 Mpc.”
