Scientists found evidence of a whole new way for stars to die

A recently-observed gamma-ray burst points to a long-hypothesized but never-before-observed way for stars to die.
Chris Young
Artist's impression of a gamma-ray burst.

An international team of astrophysicists set out to investigate the origins of a powerful gamma-ray burst (GRB) and stumbled upon a long-hypothesized but never-before-observed type of star death, a press statement reveals.

Most GRBs originate from exploding stars or neutron star mergers, but the newly observed example came from a GRB designated 191019A that formed when stars or stellar remnants in the environment surrounding a supermassive black hole collided near the core of an ancient galaxy.

Never-before-seen star collapse

A Gamma-ray burst is the strongest and brightest type of explosion ever observed by scientists. They most often occur during neutron star mergers and supernovas, and they typically signal the formation of a black hole. They also only typically last for a few seconds, making them hard to detect. The brightest ever observed to date was GRB 221009A, which was captured in October last year.

Now, the researchers behind the new discovery, who published their findings in a paper in the journal Nature Astronomy, explained that the never-before-seen type of GRB sheds new light on the diversity of the cosmos.

"For every hundred events that fit into the traditional classification scheme of gamma-ray bursts, there is at least one oddball that throws us for a loop," Northwestern University astrophysicist and study co-author Wen-fai Fong explained in the press statement. "However, it is these oddballs that tell us the most about the spectacular diversity of explosions that the universe is capable of."

Stars typically evolve in one of three predictable ways after their death, which is determined by their mass. Relatively lower-mass stars like our sun shed outer layers to eventually become white dwarf stars. Larger stars, meanwhile, explode into a supernova, creating a super-dense neutron star or black hole. Lastly, dead stars can also form a binary system that eventually collides.

The new study suggests the existence of a fourth scenario. "Our results show that stars can meet their demise in some of the densest regions of the universe, where they can be driven to collide," lead author Andrew Levan, an astronomer with Radboud University, explained in the statement. "This is exciting for understanding how stars die and for answering other questions, such as what unexpected sources might create gravitational waves that we could detect on Earth."

New GRB is 'not a typical massive star collapse'

The new GRB, which lasted a relatively long one minute, was first observed by NASA's Neil Gehrels Swift Observatory on October 19, 2019. Astronomers then carried out follow-up observations of the event's afterglow using the Gemini South telescope in Chile. Using these observations, they were able to pinpoint the location of the GRB to a relatively small region near the core of its ancient host galaxy — very near the galaxy's black hole. They discovered no evidence of a corresponding supernova.

"The lack of a supernova accompanying the long GRB 191019A tells us that this burst is not a typical massive star collapse,” Rastinejad explained. "The location of GRB 191019A, embedded in the nucleus of the host galaxy, teases a predicted but not yet evidenced theory for how gravitational-wave emitting sources might form."

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