February 21, 2024

Aside from the Big Bang itself, gamma-ray bursts (GRBs) are the most energetic events in the universe. Astronomers know some of the mechanisms that can produce them, but now a strange GRB hints at an entirely new origin—a stellar “demolition derby.”

As their name suggests, gamma-ray bursts are intense pulses of gamma radiation emitted in beams like lighthouses. The most common cause is when a massive star collapses into a black hole, but they can also occur as a result of collisions between binary star remnants such as neutron stars or white dwarfs, or possibly when a star is swallowed by a black hole. But a recent detection appears to be from a previously unknown source.

This strange thing was discovered on October 19, 2019, and has thus been designated GRB 191019A. It lasted more than a minute, classifying it as a long gamma-ray burst, usually produced by the collapse of a star. However, astronomers didn’t see any flashes of light, which would signal a supernova from a star’s collapse.

Its location suggests another origin. GRB 191019A has been tracked near the center of an ancient galaxy, where there are often a million or more stars packed into a relatively small region of space. As the supermassive black hole spins everything around it, collisions between stars become more likely, creating what the researchers describe as a stellar “destruction derby.” This is what produces gamma-ray bursts like the one detected here.

Giacomo Fragione, co-author of the study, said: “It is certainly exciting to discover these extraordinary phenomena in compact star systems, especially those orbiting supermassive black holes at the core of galaxies. “This remarkable discovery provides a tantalizing insight into the complex dynamics of these cosmic environments, establishing them as factories for events otherwise thought to be impossible.”

Gamma-ray bursts produced in this way may be common, but astronomers may miss them because these environments are often hidden in dust and gas, the team said. Discovering more information will be very valuable in understanding the death of stars and the dynamics of galaxies.

The study was published in the journal natural astronomy.

source: Northwest University