International Gemini Observatory/NOIRLab/NSF/AURA/M. Garlic/M. Zamani
When astronomers discovered a powerful gamma-ray burst (GRB) in October 2019, the most likely explanation was that it was produced by a giant, dying star in a distant galaxy in a supernova explosion. It was something However, subsequent observational data showed that the bursts resulted from collisions of stars (or their remnants) in dense regions near supermassive black holes in ancient galaxies. new paper Published in Nature Astronomy. Although such rare events have been hypothesized, this is the first observational evidence.
As previously reported, gamma-ray bursts are very high-energy bursts in distant galaxies lasting only milliseconds to hours. There are two classes of gamma ray bursts. Most (70%) are long bursts lasting more than 2 seconds, often with bright afterglows. These are usually associated with galaxies with rapid star formation. Astronomers believe that long bursts are related to the collapse of massive stars to form neutron stars and black holes (or newly formed magnetars). Baby black holes produce jets of high-energy particles that travel at near the speed of light, powerful enough to pierce the remnants of protostars, and emit X-rays and gamma rays.
Gamma-ray bursts lasting less than 2 seconds (about 30%) are considered short bursts and are usually emitted from regions with very little star formation. Astronomers believe these gamma-ray bursts are caused by the merger of two neutron stars, or a neutron star and a black hole, and form “kilonovas.”
The gamma-ray bursts detected by NASA’s Neil Gerels Swift Observatory in 2019 fell into a long category. But astronomers were puzzled when they found no evidence of a corresponding supernova. “For every 100 events that fit the traditional taxonomy of gamma-ray bursts, there is at least one strange event that keeps us stuck in a loop.” Co-author Wenhui Feng said:, an astrophysicist at Northwestern University. “But it’s these strange things that the universe tells us most about the amazing variety of possible explosions.”
Intrigued, Fong and co-authors tracked the burst’s fading afterglow using the International Gemini Observatory, supplemented by data collected by the Nordic Optical Telescope and the Hubble Space Telescope. This afterglow allowed them to locate the GRB just 100 light-years away from the core of the ancient galaxy, in close proximity to the central supermassive black hole. They concluded that this burst was caused by the collision of two of her stars or star remnants.
This is important because there are three well-known processes for a star to die, depending on its mass. Massive stars explode supernovae, while stars with the same mass as our Sun shed their outer layers, eventually fading into white dwarfs. And stellar remnants (neutron stars and black holes) created from supernovae can form binary star systems and eventually collide.
Now you have a fourth choice. Stars in dense regions of ancient galaxies can collide. This is extremely rare in active galaxies that are not very dense. An ancient galaxy could contain a million stars in a region just a few light years across. And in this case, the gravitational effects of being so close to the supermassive black hole would have altered the motion of those stars, causing them to move in random directions. There will always be conflicts.
In fact, the authors suggest that this kind of collision may not be all that uncommon. Dust and gas obscure the view of the center of the ancient galaxy, so no telltale GRBs and afterglow are detected. In the future, if astronomers can detect gravitational wave signatures associated with such GRBs, they will be able to learn more about this type of star death.
“These new results show that stars can die out in some of the densest regions of the universe where stars can collide.” Co-author Andrew Levan said:, an astronomer at Radboud University in the Netherlands. “This is interesting for understanding how stars die, and for answering other questions, such as what are the unexpected sources of gravitational waves that can be detected on Earth. ”
DOI: Natural Astronomy, 2023. 10.1038/s41550-023-01998-8 (About DOIs).
