How a Stellar Collision Created a Gamma-Ray Burst and a Magnetar
Gamma-ray bursts (GRBs) are the most energetic explosions in the universe, releasing more energy in a few seconds than the sun will in its entire lifetime. They are usually caused by the collapse of massive stars or the merger of neutron stars, but a recent discovery suggests that there might be another way to produce these cosmic fireworks.
The Mystery of GRB 191019A: A New Way to Destroy a Star
On October 19, 2019, NASA’s Neil Gehrels Swift Observatory detected a bright flash of gamma rays that lasted for about a minute. This was GRB 191019A, an unusual event that puzzled astronomers. Unlike most GRBs, which come from young and star-forming galaxies, this one came from an old and quiescent galaxy with a supermassive black hole at its center.
An international team of astrophysicists, led by Radboud University in the Netherlands and including researchers from Northwestern University, investigated the origin of this oddball GRB using data from various telescopes. They concluded that GRB 191019A was not caused by a single star or a binary system, but by the collision of stars or stellar remnants in the crowded environment around the black hole.
This scenario had been long-hypothesized but never observed before. It suggests that stars can meet their demise in some of the densest regions of the universe, where they can be driven to collide by the strong gravitational forces and high velocities. The collision can then trigger a powerful explosion that emits gamma rays and other radiation.
Cosmic Fireworks: The Collision of Stars in an Ancient Galaxy
The researchers also found evidence that GRB 191019A produced a magnetar, a highly magnetized neutron star that spins rapidly and emits intense beams of radiation. Magnetars are rare and exotic objects that can also result from massive star explosions or neutron star mergers. The formation of a magnetar in this case adds another layer of complexity and mystery to this remarkable event.
“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,” said Northwestern astrophysicist and study co-author Wen-fai Fong. “However, it is these oddballs that tell us the most about the spectacular diversity of explosions that the universe is capable of.”
The study was published on June 22, 2023, in the journal Nature Astronomy12.
