Odd gamma ray burst may be from a smash-up between two dead stars

A wierd flash of gamma rays from house is upending our concepts on stellar collisions. This gamma ray burst (GRB) appears to have come from two stars smashing collectively close to the centre of an previous galaxy, a vastly completely different origin from different occasions prefer it.

There are two sorts of GRBs: quick ones, which final two seconds or much less, and lengthy ones. Long GRBs are usually thought to happen when an enormous star explodes in a supernova, whereas most quick GRBs appear to return from binary neutron stars – extremely dense stellar corpses – smashing collectively.

The one in query, known as GRB191019A, was a protracted GRB, however nonetheless appears to have come from two useless stars, or probably a star and a black gap, colliding.

Anya Nugent at Northwestern College in Illinois and her colleagues used knowledge from six observatories to dig into the main points of highly effective blast, which occurred in 2019 and lasted slightly over one minute. They discovered that the burst got here from near the centre of a galaxy about 3.3 billion gentle years away, however noticed no trace of the supernova anticipated to be required for a protracted GRB.

These supernovae are usually extra widespread in younger, lively galaxies, however this galaxy is extraordinarily previous. Most of its huge stars have already gone by means of the primary part of their lives and developed into neutron stars, white dwarfs and black holes. As a result of GRB191019A got here from so near the centre of its galaxy, the place these stellar corpses whiz round in abundance, the researchers discovered that it’s most definitely two of them collided to create this blast of radiation.

We’ve by no means seen such concrete proof of two stars colliding in this type of surroundings earlier than, says Nugent. “With binary neutron stars, we expect they’re born collectively, they die collectively, and ultimately merge collectively,” she says. “That is our first observational proof that these stars weren’t born collectively: they have been born, they died, and ultimately of their dying they discovered one another.”

However it’s nonetheless puzzling how one among these stellar collisions might produce a full minute of radiation as a substitute of the short flare typical of quick GRBs.

“The concept lengthy GRBs might come from mergers is admittedly throwing a whole lot of astronomers for a loop – we nonetheless want to determine how we might even be getting this a lot emission,” says Nugent. The workforce hopes that recognizing extra GRBs like this might assist unravel the thriller.