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

A wierd flash of gamma rays from area 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 forms of GRBs: quick ones, which final two seconds or much less, and lengthy ones. Long GRBs are typically thought to happen when an enormous star explodes in a supernova, whereas most quick GRBs appear to come back from binary neutron stars – extremely dense stellar corpses – smashing collectively.

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

Anya Nugent at Northwestern University in Illinois and her colleagues used knowledge from six observatories to dig into the small print of highly effective blast, which occurred in 2019 and lasted a bit 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.

Those supernovae are usually extra widespread in younger, lively galaxies, however this galaxy is extraordinarily previous. Most of its large stars have already gone by the principle section of their lives and advanced into neutron stars, white dwarfs and black holes. Because 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 probably 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 sort of setting earlier than, says Nugent. “With binary neutron stars, we think they’re born together, they die together, and eventually merge together,” she says. “This is our first observational evidence that these stars weren’t born together: they were born, they died, and eventually in their death they found each other.”

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

“The idea that long GRBs could come from mergers is really throwing a lot of astronomers for a loop – we still need to figure out how we could even be getting this much emission,” says Nugent. The crew hopes that recognizing extra GRBs like this might assist unravel the thriller.