Gamma-ray bursts don’t always come from black holes


Some short-lived cosmic gamma-ray bursts (GRBs) are triggered by the birth of a supermassive star -a neutron star remnant-and not by a black hole.

Until now, space scientists have largely agreed that the “engine” that drives such short-lived, energetic bursts must always come from a newly formed black hole: a region of space-time where gravity is so strong that nothing, not even light, can escape it.

However, new research from an international team of astrophysicists, led by Dr Nuria Jordana-Mitjans of the University of Bath, challenges this scientific orthodoxy. They publish results in The AstrophysicalJournal.

Dr. Jordana-Mitjans said it’s a statement: “These findings are important as they confirm that newborn neutron stars can power some short-lived GRBs and the bright emissions across the electromagnetic spectrum that have been detected accompanying them. This discovery may offer a new way to locate neutron mergers.” neutron stars, and therefore gravitational wave emitters, when we look for signals in the heavens.”

Much is known about short-lived GRBs. They begin life when two neutron stars, which have been spiraling closer and closer, accelerating steadily, finally collide. And from the crash site, a launched explosion releases the gamma-ray radiation that produces a GRB, followed by a longer-lasting afterglow. A day later, radioactive material that was ejected in all directions during the explosion produces what researchers call a kilonova..

However, precisely what remains after the collision of two neutron stars, the “product” of the collision, and consequently the energy source that gives a GRB its extraordinary energy, has been a matter of debate for a long time. weather. Scientists may now be closer to settling this debate, thanks to the findings of the Bath-led study.

Space scientists are torn between two theories. The first theory says that neutron stars merge to briefly form an extremely massive neutron star, only for this star to collapse into a black hole in a fraction of a second. The second argues that the two neutron stars would result in a lighter neutron star with a longer life expectancy.

So the question that has been plaguing astrophysicists for decades is this: are short-lived GRBs powered by a black hole or by the birth of a long-lived neutron star?

To date, most astrophysicists have supported the black hole theory and there was agreement that to produce a GRB it is necessary for the massive neutron star to collapse almost instantaneously.

Astrophysicists learn about neutron star collisions by measuring the electromagnetic signals of the resulting GRBs. The signal originating from a black hole would be expected to differ from that from a neutron star remnant.

The electromagnetic signal from the GRB explored for this study (named GRB 180618A) made it clear to Dr. Jordana-Mitjans and her collaborators that a neutron star remnant, rather than a black hole, must have caused this outburst.

Elaborating, Dr Jordana-Mitjans said: “For the first time, our observations highlight multiple signals from a surviving neutron star that lived for at least a day after the death of the original neutron star binary.”