Unusually Powerful Gamma-Ray Burst Linked to Neutron Star Merger
Scientists have made a groundbreaking discovery by linking an unusually powerful gamma-ray burst (GRB 211211A) to a neutron star merger. This remarkable event, which emitted an excess of infrared light, was identified as a kilonova, an occurrence that is believed to transpire when neutron stars collide.
The gamma-ray burst, labeled GRB 211211A, was detected in December 2021 by NASA’s Neil Gehrels Swift Observatory and the Fermi Gamma-ray Space Telescope. Typically, gamma-ray bursts last anywhere from a few milliseconds to several hours. However, GRB 211211A persisted for about a minute, differentiating it from the collapse of a massive star into a supernova. Its peculiar qualities, including the abundance of infrared light and its faster-fading nature, hinted at a unique phenomenon.
In a recent study published in the journal Nature, an international team of scientists unveiled that the infrared light emitted during the burst originated from a kilonova. Kilonovae are rare events that occur during the collision of neutron stars or a neutron star and a black hole, producing heavy elements like gold and platinum. Previously, kilonovae had only been associated with gamma-ray bursts that lasted less than two seconds.
The research was led by Jillian Rastinejad from Northwestern University, with contributions from physicists from the University of Birmingham, the University of Leicester, and Radboud University. Dr. Matt Nicholl, an Associate Professor at the University of Birmingham, modeled the kilonova emission and reported that the event produced about 1,000 times the mass of the Earth in heavy elements. This finding supports the notion that kilonovae are major contributors to the production of gold in the Universe.
While it is suspected that up to 10 percent of long gamma-ray bursts are caused by the merging of neutron stars or neutron stars and black holes, no solid evidence in the form of kilonovae had been identified until now. Dr. Gavin Lamb, a post-doctoral researcher at the University of Leicester, explained that by modeling the afterglows of gamma-ray bursts, one can uncover any additional emission components like kilonovae or supernovae.
The significance of GRB 211211A lies in the fact that it is the closest kilonova to have been discovered without gravitational waves. This proximity, in a neighboring galaxy approximately 1 billion light years away, allowed scientists to study the merger’s properties in unprecedented detail. The findings have exciting implications for the upcoming gravitational wave observation run, scheduled to commence in 2023.
Furthermore, the team identified how the jet of high-energy electrons responsible for causing the gamma-ray burst changed over time. The cooling down of this jet was found to be responsible for the longer-lasting emission of GRB 211211A. The researchers believe that studying more events like this one will shed light on other enigmatic gamma-ray bursts that do not align with standard interpretations.
Dr. Benjamin Gompertz, Assistant Professor at the University of Birmingham and lead author of a related paper in Nature Astronomy, described GRB 211211A as a “remarkable” gamma-ray burst. Typically, mergers last no more than two seconds, but this particular event powered a jet for almost a full minute. While it is possible that the behavior is explained by a long-lasting neutron star, the researchers have not ruled out the possibility that what they observed was a neutron star being torn apart by a black hole. The detailed information gathered from GRB 211211A will be pivotal in determining the correct interpretation.
The study was funded by the European Research Council under the KilonovaRank project, which leverages Big Data to investigate significant cosmic events.