An international team of astrophysicists may have discovered a novel method for destroying a star while looking for the origins of a powerful gamma-ray burst (GRB).
Albeit most GRBs begin from detonating enormous stars or neutron-star consolidations, the specialists reasoned that GRB 1910-19A rather came from the impact of stars or heavenly remainders in the tough, pressed climate encompassing a supermassive dark opening at the center of an old cosmic system. The environment that resembles a demolition derby points to a long-hypothesized but never-before-seen method for destroying a star and producing a GRB.
Nature Astronomy was the journal that published the study. The astronomers from Northwestern University were a part of the research team, which was led by Radboud University in the Netherlands.
“For every hundred gamma-ray burst events that fit into the traditional classification scheme, there is at least one oddball that throws us for a loop, but it is these oddballs that tell us the most about the spectacular diversity of explosions that the universe is capable of.”
Northwestern astrophysicist and study co-author Wen-fai Fong,
According to Northwestern astrophysicist and study co-author Wen-fai Fong, “there is at least one oddball that throws us for a loop.” However, “it is these oddballs that tell us the most about the spectacular diversity of explosions that the universe is capable of,” Fong said. “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.”
Giacomo Fragione, a Northwestern astrophysicist and co-author of the study, stated, “The discovery of these extraordinary phenomena within dense stellar systems, especially those encircling supermassive black holes at the cores of galaxies, is undeniably exciting.” This remarkable finding provides us with a tantalizing glimpse into the intricate dynamics at work within these cosmic environments, establishing them as factories for events that would otherwise be thought impossible.”
Fong is a member of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and an assistant professor of physics and astronomy at Northwestern University’s Weinberg College of Arts and Sciences. At CIERA, Fragione works as a research assistant professor. Anya Nugent and Jillian Rastinejad, both Ph.D. students in astronomy and members of Fong’s research group, are two additional Northwestern co-authors.
Depending on their mass, most stars die in one of three predictable ways. White dwarf stars eventually form when relatively low-mass stars like our sun reach old age and shed their outer layers. In contrast, in cataclysmic supernova explosions, massive stars burn brighter and explode faster, resulting in extremely dense objects like neutron stars and black holes. The third scenario is when two of these stellar remnants collide and form a binary system.
However, the new study suggests that there may be a fourth choice.
Lead author Andrew Levan, an astronomer at Radboud University, stated, “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.” This is exciting for figuring out how stars die and answering other questions, like what unidentified sources might produce gravitational waves that could be detected on Earth.
Few, if any, massive stars are still present in ancient galaxies, which have outlived their star-forming potential. White dwarfs, neutron stars, and black holes are just a few of the extremely dense remnants of stars that can be found in their cores. Astronomers have known for a long time that it would only be a matter of time before two stellar objects collided to produce a GRB in the tumultuous beehive of activity surrounding a supermassive black hole. However, there remains a lack of evidence for that kind of merger.
A brief burst of gamma rays lasting just over a minute was detected by NASA’s Neil Gehrels Swift Observatory on October 19, 2019, giving astronomers their first indication of such an event. “Long” refers to any GRB lasting longer than two seconds. The collapse of stars with masses at least ten times that of our sun typically causes such bursts.
The researchers then used the Chilean Gemini South telescope, which is part of the International Gemini Observatory and is operated by the NOIRLab of the National Science Foundation, to observe the GRB’s waning afterglow over time.
The astronomers were able to locate the GRB in a region less than 100 light-years from the nucleus of an ancient galaxy, very close to the galaxy’s supermassive black hole, thanks to these observations. Curiously, the researchers also didn’t find any evidence of a matching supernova, which would have affected the light that Gemini South picked up.
Rastinejad, who conducted calculations to ensure that the data did not conceal a supernova, stated, “The lack of a supernova accompanying the long GRB 191019A tells us that this burst is not a typical massive star collapse.” GRB 191019A’s location, embedded in the host galaxy’s nucleus, suggests a theory for the formation of gravitational-wave emitting sources that has been predicted but not proven.”
Long GRBs from colliding stellar remnants like neutron stars and black holes are extremely uncommon in typical galactic environments. However, the cores of ancient galaxies are anything but typical, with up to a million stars packed into a few light-years-wide areas.
Under the massive gravitational pull of a supermassive black hole, which would cause the motions of stars to be disrupted and send them careening in any direction, such a high population density may allow for occasional stellar collisions. At some point, these errant stars would come together, causing a titanic explosion that could be seen from far away in the universe.
Nugent, who was responsible for crucial modeling of the host galaxy, stated, “This event confounds almost every expectation we have for the environments of short and long GRBs.”
“Short GRBs, with their merger origins, have not been observed to be so connected to the nuclei of their hosts, whereas long GRBs are never found in galaxies as old and dead as the host of GRB 191019A.” The discovery of this event in the core of its old, dormant galaxy opens up promising new possibilities for the formation of rarely observed binary systems.”
It’s possible that such occurrences have gone unnoticed up to this point in similarly populated regions of the universe. The galactic centers’ overabundance of dust and gas may have obscured both the GRB’s initial flash and its subsequent afterglow, which could account for their obscurity. Astronomers may be able to observe the burst and its effects thanks to the possible exception of GRB 191019A.
According to Fong, “even though this event is the first of its kind to be discovered, it’s possible that there are more out there that are hidden by the large amounts of dust close to their galaxies.” Indeed, if compact objects combine during this long-lasting event, it contributes to the expanding population of GRBs that defy our conventional classifications.”
By attempting to find a greater number of these occasions, the scientists desire to coordinate a GRB discovery with a related gravitational-wave identification, which would uncover more about their real essence and affirm their beginnings—eeven in the murkiest of conditions. The Vera C. Rubin Observatory, when it comes online in 2025, will be significant in this sort of exploration.
The review, “A long-span gamma-beam eruption of dynamical beginnings from the core of an old world,” is distributed in Nature Cosmology.
More information: Levan, A.J., et al. A long-duration gamma-ray burst of dynamical origin from the nucleus of an ancient galaxy. Nature Astronomy (2023). DOI: 10.1038/s41550-023-01998-8.
