Artist’s impression of a gamma-ray burst that will have come from useless stars crashing into one another
Worldwide Gemini Observatory/NOIRLab/NSF/AURA/M. Garlick/M. Zamani
An odd 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 totally different origin from different occasions prefer it.
There are two kinds of GRBs: brief ones, which final two seconds or much less, and lengthy ones. Lengthy GRBs are usually thought to happen when a large star explodes in a supernova, whereas most brief GRBs appear to come back from binary neutron stars – extremely dense stellar corpses – smashing collectively.
The one in query, known as GRB191019A, was a protracted GRB, however however 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 information from six observatories to dig into the main points 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 mild years away, however noticed no trace of the supernova anticipated to be required for a protracted GRB.
These supernovae are typically extra frequent in younger, lively galaxies, however this galaxy is extraordinarily previous. Most of its huge stars have already gone via the primary section 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 type of setting earlier than, says Nugent. “With binary neutron stars, we expect they’re born collectively, they die collectively, and finally merge collectively,” she says. “That is our first observational proof that these stars weren’t born collectively: they have been born, they died, and finally of their demise 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 fast flare typical of brief GRBs.
“The concept lengthy GRBs might come from mergers is de facto throwing a number of astronomers for a loop – we nonetheless want to determine how we might even be getting this a lot emission,” says Nugent. The staff hopes that recognizing extra GRBs like this might assist unravel the thriller.
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