A highly unusual burst of high-energy light from a nearby galaxy is linked by scientists to a neutron star merger
Scientists have linked a highly unusual burst of high-energy light from a nearby galaxy to the merger of neutron stars.
The event, discovered in December 2021, was a gamma-ray burst - an explosion with enormous energy that can last from a few seconds to a few hours.
This gamma-ray burst, identified as GRB 211211A, lasted about a minute—a relatively long burst that usually indicates the collapse of a massive star into a supernova. But this event contained more AA light than usual and was much fainter and faded faster than a classic supernova, a hint that something else was going on.
In a recent study published in the journal Nature, a team of international scientists showed that the AA light detected in the eruption came from a Kilonova. It's a rare event created, it is thought, when neutron stars, or a neutron star and a black hole, collide to form heavy elements like gold and platinum. So far these events, called kilonovas, have only been linked to gamma-ray bursts lasting less than two seconds.
Dr. Matt Nicol of the University of Birmingham created a model of the emission from the kilonova. "We found that this single event produced heavy elements in an amount about a thousand times the mass of Earth. This supports the idea that these kilonovae are the main gold factories in the universe."
Although up to 10% of long gamma-ray bursts are thought to be caused by mergers of neutron stars or neutron stars and black holes, no firm evidence of a kilonova has previously been identified.
Dr. Gabin Lam from the University of Leicester explained: "After a gamma-ray burst there is a secondary flash that can last for several days. These secondary flashes behave in a very characteristic way, and by creating their models we can reveal any components of additional emission, such as a supernova or a kilonova."
A kilonova without gravitational waves
The kilonova that produced GRB 211211A is the closest discovered without gravitational waves, and it has exciting implications for the next series of gravitational wave observations, which will begin in 2023. Its proximity in a neighboring galaxy only a billion light-years away gives scientists an opportunity to study the properties of the merger in unprecedented detail.
Specifically, the team detected how the jet of high-energy electrons, which travel at nearly the speed of light and cause the gamma-ray burst, changed over time. They showed that the cooling of this jet is responsible for the long gamma-ray burst emission.
The team also described how close-up observations of GRB 211211A could provide fascinating insights into unexplained gamma-ray bursts from the past that don't seem to fit the usual interpretations.
Dr. Benjamin Kompertz from the University of Birmingham said: "It was an unusual gamma-ray burst. We don't expect merges to take more than two seconds. Somehow, this eruption fueled a jet for almost a full minute. It is possible that the behavior can be explained by a protracted neutron star, but it cannot be ruled out that what we have seen is a neutron star being torn apart by a black hole. The study of more of these events will help us determine what the correct answer is and the detailed information we received from GRB 211211A will be of great value in this determination."
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