admin While searching for the origins of a powerful gamma-ray burst (GRB), an international team of astrophysicists may have stumbled upon a new way to destroy a star.
Although most GRBs come from massive stellar explosions or neutron star mergers, the researchers concluded that GRB 191019A instead formed from the collision of stars or stellar remnants in the densely populated environment around a supermassive black hole at the heart of an ancient galaxy. A demolition derby-like environment suggests a hypothetical but never-before-seen possibility of destroying a star and creating a GRB.
The study was published in the journal Nature Astronomy. The research team, led by Radboud University in the Netherlands, consisted of astronomers from Northwestern University.”For every 100 events that fit the traditional gamma-ray burst classification scheme, there is at least one weirdo that puts us in a loop,” said Wen-fai Fong, a Northwestern astrophysicist and co-author of the study. whether these monsters can tell us more about the spectacular variety of explosions the universe is capable of.
“The discovery of these extraordinary phenomena in dense star systems, particularly those surrounding supermassive black holes at the heart of galaxies, is undeniably exciting,” said Giacomo Fragione, a Northwestern astrophysicist and co-author of the study. “This remarkable discovery gives us an enticing glimpse into the complex dynamics at work in these cosmic environments, turning them into factories for events that would otherwise be thought impossible.
“Fong is an assistant professor of physics and astronomy at the Weinberg College of Arts and Sciences in the Northwest and a member of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). Fragione is a professor at CIERA. Other Northwest contributors include Anya Nugent and Jillian Rastinejad, both Ph.D.D. Astronomy students and members of Fong’s research team.
Most stars die in one of three predictable ways, depending on their mass. As relatively low-mass stars like our Sun reach old age, they shed their outer layers and eventually disappear, becoming white dwarfs. On the other hand, more massive stars burn brighter and explode faster in catastrophic supernova explosions, creating ultradense objects like neutron stars and black holes.
The third scenario is that two of these stellar remnants form a binary star system and eventually collide.
However, a new study shows there may be a fourth option.”Our results show that stars can die in some of the densest regions of the Universe, where they can collide,” said lead author Andrew Levan, an astronomer at Radboud University. “It’s exciting to understand how stars die and to answer other questions like unexpected sources that can generate gravitational waves that we might detect on Earth.”Long after star formation, old galaxies have few or no massive stars. However, their cores are full of stars and a menagerie of ultradense stellar debris such as white dwarfs, neutron stars, and black holes.
Astronomers have long suspected that in the turbulent frenzy surrounding a supermassive black hole, it will only be a matter of time before two stellar objects collide and GRBs form. However, there is still no evidence for this type of fusion.
On October 19, 2019, astronomers spotted the first signs of such an event when NASA’s Neil Gehrel’s Swift Observatory spotted a bright burst of gamma rays that lasted just over a minute. Any GRB lasting longer than two seconds is considered “long”.
“These flares are typically caused by the collapse of stars at least 10 times the mass of our Sun.Scientists then used the Gemini South Telescope in Chile, part of the Gemini International Observatory operated by the National Science Foundation’s NOIRLab, to conduct long-term observations of the afterglow of the GRB’s disappearance.
These observations allowed astronomers to locate the GRB in a region less than 100 light-years from the core of the old galaxy, very close to that galaxy’s supermassive black hole. Interestingly, scientists have also found no evidence that an actual supernova left its mark in the light captured by Gemini South.
“The lack of a supernova accompanying the long GRB 191019A tells us that this explosion is not a typical massive star collapse,” said Rastinejad, who performed the calculations to ensure the supernova wasn’t hiding in the data.
“The position of GRB 191019A, embedded in the core of its host galaxy, suggests a predicted but as yet unproven theory of how gravitational-wave emission sources might form.”In typical galactic environments, the production of long GRBs from colliding stellar remnants such as neutron stars and black holes is extremely rare. However, the cores of old galaxies are not typical, and a million or more stars can reside in a region a few light-years across.
Such extreme population densities could be so great that there could be occasional collisions between stars, particularly under the gigantic gravitational pull of a supermassive black hole, that would disrupt the motions of the stars and send them flying in random directions. Eventually the paths of these unruly stars would cross and merge, triggering a gigantic explosion that could be observed from vast cosmic distances.
“This event exceeds almost all of our expectations for the surroundings of the short and long GRB,” said Nugent, who performed key modeling of the host galaxy.
“While long GRBs have never been found in old and dead galaxies like the parent galaxy GRB 191019A, short GRBs with their fusion origins have not been observed to be associated with their host nuclei. The discovery of this event at the center of its “The ancient galaxy at rest opens the door to promising new avenues for binary star formation that have rarely been observed before.
“It is possible that such events occur regularly in similarly populated regions of the Universe, but have so far gone unnoticed. One possible reason for their darkness is that the galaxies’ centers are filled with dust and gas, which can obscure both the initial GRB flash and the afterglow.
Possibly the rare exception, GRB 191019A allows astronomers to spot the flare and study its aftermath.”Although this event is the first of its kind to be detected, it’s possible there are others that are obscured by large amounts of dust near their galaxies,” Fong said. “If this long-lived event results from the merging of compact objects, it actually contributes to a growing population of GRBs that challenges our traditional classifications.”
By working to discover more of these events, the researchers hope to match a GRB detection with a corresponding gravitational-wave detection, which would reveal more about their true nature and confirm their origins—even in the murkiest of environments. The Vera C. Rubin Observatory, when it comes online in 2025, will be invaluable in this kind of research.
The study, “A long-duration gamma-ray burst of dynamical origin from the nucleus of an ancient galaxy,” is published in Nature Astronomy.
