An odd 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 totally different origin from different occasions prefer it.
There are two forms of GRBs: brief ones, which final two seconds or much less, and lengthy ones. Lengthy GRBs are usually thought to happen when an enormous star explodes in a supernova, whereas most brief GRBs appear to return from binary neutron stars – extremely dense stellar corpses – smashing collectively.
The one in query, referred to as GRB191019A, was a protracted GRB, however however appears to have come from two lifeless 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 a bit of 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 frequent in younger, energetic galaxies, however this galaxy is extraordinarily previous. Most of its large stars have already gone by way of the principle 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 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 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 loss of life they discovered one another.”
But it surely’s nonetheless puzzling how certainly one of these stellar collisions may produce a full minute of radiation as an alternative of the fast flare typical of brief GRBs.
“The concept that lengthy GRBs may come from mergers is basically throwing plenty of astronomers for a loop – we nonetheless want to determine how we may even be getting this a lot emission,” says Nugent. The group hopes that recognizing extra GRBs like this might assist unravel the thriller.