Astronomers studying a powerful gamma-ray burst (GRB) with the International Gemini Observatory, operated by NSF’s NOIRLab, may have observed a never-before-seen way to destroy a star. Unlike most GRBs, which are caused by exploding massive stars or the chance mergers of neutron stars, astronomers have concluded that this GRB came instead from the collision of stars or stellar remnants in the jam-packed environment surrounding a supermassive black hole at the core of an ancient galaxy. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/M. Garlick/M. Zamani. download: Large JPEG
This artist's impression illustrates how astronomers studying a powerful gamma-ray burst (GRB) with the Gemini South telescope, operated by NSF’s NOIRLab, may have detected a never-before-seen way to destroy a star. Unlike most GRBs, which are caused by exploding massive stars or the chance mergers of neutron stars, astronomers have concluded that this GRB came instead from the collision of stars or stellar remnants in the jam-packed environment surrounding a supermassive black hole at the core of an ancient galaxy. Credit:International Gemini Observatory/NOIRLab/NSF/AURA, M. Garlick, M. Zamani, K. O Chul, ESO/L. Calçada, NASA's Goddard Space Flight Center/CI Lab, N. Bartmann. Music: Stellardrone - Airglow. Load Video
Most stars in the Universe die in predictable ways, depending on their mass. Relatively low-mass stars like our Sun slough off their
outer layers in old age and eventually fade to become white dwarf stars. More massive stars burn brighter and die sooner in cataclysmic supernova explosions, creating ultradense objects like neutron stars and black holes.
If two such stellar remnants form a binary system, they also can
eventually collide. New research, however, points to a
long-hypothesized, but never-before-seen, fourth option.
While searching for the origins of a long-duration gamma-ray burst (GRB), astronomers using the Gemini South telescope in Chile, part of the International Gemini Observatory
operated by NSF’s NOIRLab, and other telescopes [1], have uncovered
evidence of a demolition-derby-like collision of stars or stellar
remnants in the chaotic and densely packed region near an ancient
galaxy’s supermassive black hole.
“These new results show that stars can meet their demise in some
of the densest regions of the Universe where they can be driven to
collide,” said Andrew Levan, an astronomer with Radboud University
in The Netherlands and lead author of a paper appearing in the journal Nature Astronomy. “This
is exciting for understanding how stars die and for answering other
questions, such as what unexpected sources might create gravitational
waves that we could detect on Earth.”
Ancient galaxies are long past their star-forming prime and would
have few, if any, remaining giant stars, the principal source of long
GRBs. Their cores, however, are teeming with stars and a menagerie of
ultra-dense stellar remnants, such as white dwarf stars, neutron stars,
and black holes. Astronomers have long suspected that in the turbulent
beehive of activity surrounding a supermassive black hole, it would only
be a matter of time until two stellar objects collide to produce a GRB.
Evidence for that type of merger, however, has been elusive.
The first hints that such an event had occurred were seen on 19 October 2019 when NASA’s Neil Gehrels Swift Observatory
detected a bright flash of gamma rays that lasted for a little more
than one minute. Any GRB lasting more than two seconds is considered
“long.” Such bursts typically come from the supernova death of stars at
least 10 times the mass of our Sun — but not always.
The researchers then used Gemini South to make long-term observations
of the GRB’s fading afterglow to learn more about its origins. The
observations allowed the astronomers to pinpoint the location of the GRB
to a region less than 100 light-years from the nucleus of an ancient
galaxy, which placed it very near the galaxy’s supermassive black hole.
The researchers also found no evidence of a corresponding supernova,
which would leave its imprint on the light studied by Gemini South.
“Our follow-up observation told us that rather than being a
massive star collapsing, the burst was most likely caused by the merger
of two compact objects,” said Levan. “By pinpointing its
location to the center of a previously identified ancient galaxy, we had
the first tantalizing evidence of a new pathway to ‘kill’ a star.”
It is possible that such events occur routinely in similarly crowded regions across the Universe but have gone unnoticed until this point. A possible reason for their obscurity is that galactic centers are brimming with dust and gas, which could obscure both the initial flash of the GRB and the resulting afterglow. This particular GRB, identified as GRB 191019A, may be a rare exception, allowing astronomers to detect the burst and study its after effects.
The researchers would like to discover more of these events. Their hope is 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.
“Studying gamma-ray bursts like these is a great example of how the field is really advanced by many facilities working together, from the detection of the GRB, to the discoveries of afterglows and distances with telescopes like Gemini, through to detailed dissection of events with observations across the electromagnetic spectrum,” said Levan.
“These observations add to Gemini’s rich heritage developing our understanding of stellar evolution,” says Martin Still, NSF’s program director for the International Gemini Observatory. “The time sensitive observations are a testament to Gemini’s nimble operations and sensitivity to distant, dynamic events across the Universe.”
More Information
Reference: Levan, A. J., Malesani, D. B., Gompertz,
B. P., et al. (2023) “A long-duration gamma-ray burst of dynamical
origin from the nucleus of an ancient galaxy.” Nature Astronomy. DOI: 10.1038/s41550-023-01998-8
[1] Additional observations were made with the Nordic Optical Telescope and the NASA/ESA Hubble Space Telescope.
NSF’s NOIRLab, the US center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (operated in cooperation with the Department of Energy’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson,
Arizona. The astronomical community is honored to have the opportunity
to conduct astronomical research on Iolkam Du’ag (Kitt Peak) in Arizona,
on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile.
We recognize and acknowledge the very significant cultural role and
reverence that these sites have to the Tohono O’odham Nation, to the
Native Hawaiian community, and to the local communities in Chile,
respectively.
Links
Contacts:
Andrew Levan
Radboud University
Email: a.levan@astro.ru.nl
Charles Blue
Public Information Officer
NSF’s NOIRLab
Tel: +1 202 236 6324
Email: charles.blue@noirlab.edu
