An international assembly of astronomers has detected a long gamma-ray burst emanating from an ancient galaxy, suggesting that this occurrence was likely a result of the merger of two separate neutron stars. This discovery challenges established beliefs about the origins of such bursts. By utilizing an array of telescopes, the team analyzed the gamma-ray burst of 2019, and while they are contemplating other possible causes, they believe future observations will shed more light on the source of this event.
For the first time, astronomers worldwide have noted a long gamma-ray burst located near the core of an ancient galaxy, a remarkable discovery as such bursts are usually attributed to the collapse of massive stars or long-duration orbits of neutron stars, occurrences not expected in the heart of an ancient galaxy. The findings, led by Andrew Levan of Radboud University, have been reported in the journal Nature Astronomy.
Until recently, the consensus was that long gamma-ray bursts, lasting several seconds, could only result from a very massive star’s collapse into a supernova at its life’s end. A second possible trigger for these bursts was identified in 2022 when two sizeable stars, having orbited each other throughout their lifespan, transformed into neutron stars and collided, creating a kilonova. As of 2023, a third potential source for long gamma-ray bursts has emerged.
“Our findings point to the merger of two independent neutron stars, not ones that have been in a binary system their entire lives,” explains principal investigator Andrew Levan from Radboud University. “We surmise that the gravitational forces from the abundant stars at the galaxy’s heart drew the neutron stars together.”
The research group studied the aftermath of a gamma-ray burst detected by the Neil Gehrels Swift Observatory on October 19, 2019, utilizing the Gemini South telescope in Chile, the Nordic Optical Telescope on the Canary Island of La Palma, and the Hubble Space Telescope.
Their investigations revealed that the burst originated near the core of an ancient galaxy, offering two compelling reasons to believe that two sources merged to produce it.
Firstly, ancient galaxies typically lack heavy stars that could implode into supernovae, as these stars are more commonly found in younger galaxies. Furthermore, the bright optical light characteristic of supernovae was absent in this instance.
The second line of reasoning is that galaxy cores are crowded regions, home to hundreds of thousands of various stars, white dwarfs, neutron stars, black holes, and dust clouds, all orbiting a supermassive black hole. Collectively, over 10 million stellar and non-stellar objects are packed into an area spanning only a few light-years. “This space is roughly equivalent to the distance between our Sun and its nearest star,” explains Levan. “Therefore, the odds of a collision at the center of a galaxy are far greater than in its peripheries, where our location would be.”
The scientists remain open to other explanations, acknowledging that the lengthy gamma-ray burst could also be the result of collisions involving other compact objects like black holes or white dwarfs. They hope to simultaneously observe long gamma-ray bursts and gravitational waves in the future, enabling them to make more definitive conclusions about the radiation’s source.
Read more about this discovery:
Star Annihilation: A New Approach
Reference: “A long-duration gamma-ray burst of dynamical origin from the nucleus of an ancient galaxy” by Andrew J. Levan, et al., 22 June 2023, Nature Astronomy.
Frequently Asked Questions (FAQs) about Gamma-Ray Burst
What is the new discovery about gamma-ray bursts?
An international team of astronomers has discovered a long gamma-ray burst in an ancient galaxy, likely caused by the merger of two separate neutron stars. This challenges conventional understanding about the causes of such bursts.
Who led the research team that made the discovery?
The research team was led by Andrew Levan of Radboud University.
Where was the gamma-ray burst detected?
The gamma-ray burst was detected near the center of an ancient galaxy.
What are the typical causes of long gamma-ray bursts?
Long gamma-ray bursts are typically caused by the collapse of massive stars or when neutron stars orbit each other for a long time.
What’s different about this gamma-ray burst?
Unlike typical bursts, the researchers believe this one occurred due to the merging of two independent neutron stars, drawn together by the gravitational forces at the galaxy’s heart.
What are the potential alternative causes of the gamma-ray burst?
The researchers propose that the prolonged gamma-ray burst could also result from the collision of other compact objects, like black holes or white dwarfs.
What are the researchers’ future hopes?
The researchers hope to be able to observe long gamma-ray bursts simultaneously with gravitational waves in the future, which would help them make more definitive conclusions about the origin of the radiation.
More about Gamma-Ray Burst
- Long-duration Gamma-ray Burst of Dynamical Origin
- About Gamma-Ray Bursts
- Neil Gehrels Swift Observatory
- Hubble Space Telescope
- Gemini South Telescope
- Nordic Optical Telescope