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A rare kilonova explosion, in which two neutron stars appear to have merged to create a larger neutron star called a magnetar, has been observed by astronomers studying short-lived gamma-ray bursts (GRBs).
Wen-fai Fong, an astrophysicist at the University of the Northwest in the United States, has been researching these brief gamma-ray bursts for a decade. “When you think you understand them, they throw you a new twist. The Universe produces such a diversity of explosions”, the expert She said.
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Immense bursts of gamma rays are created by the orbit of binary stars. These GRBs are so powerful that they can be detected light years away. It appears that GRBs can only be created under perfect conditions that allow it.
What is Short GRB?
Short GRBs are short bursts of gamma rays, heralding electrifying events in distant galaxies. According to Fong, experts assume they come from the merger of two neutron stars.
As the name suggests, Fong said that GRBs occur instantaneously – there and gone within seconds. But a residual glow of anything from X-rays to radio and infrared emissions will accompany them.
This means that it is all hands on the bridge to pass as many astronomical instruments as possible over it when a short GRB is detected, until the glow wears off. “It’s a sign that fades quickly,” says Fong. The blast disappears from the time you have lunch to the time of dinner, “(although there is usually time for a few days to research it).
This afterglow, he says, indicates that some short GRBs come from kilonova bursts in which some of those stars’ mass is ejected into space by the merger of neutron stars. (The name suggests they are about 1000 times more powerful than stellar nova explosions, but far less powerful than supernova explosions that mark the deaths of giant stars.)
If you wanted to make a smoothie and didn’t put the lid on the blender, Fong compares it to what might happen, except in this case it’s bits of neutron star that are blown out all over the place.
Can they explain the new GRB?
These neutrons easily fuse into unstable isotopes of heavy elements, which then rapidly decay into more stable ones, releasing heat, light, X-rays and radio waves in the process. But there was something that did not fit the model for a short GRB detected on May 22 (called GRB 200522A).
Three and a half days after the GRB, when the Hubble Space Telescope was free to pause other observations and head towards the source of GRB 200522A, astronomers noticed that it released ten times more infrared light than a typical kilonova. It just didn’t align, considering what we know about the radio and the X-rays of this explosion, “Fong says.”
His team gradually realized that they had seen something really strange.
Mergers of neutron stars usually create black holes. His team was able to find the only reason they had witnessed the birth of a magnetar is that such a merger could create a ten times brighter glow in the infrared.
Magnetars are neutron stars with incredibly high magnetic fields. As it rotated rapidly after the collision that formed it, this magnetar’s field transferred energy to the debris produced by the kilonova explosion, heating it and causing it to glow exactly the way Hubble observed.
In itself it is already exciting enough. But while GRB 200522A is a long way off in a galaxy, the discovery is also important to our lives here on Earth.
Scientists once believed that what produced elements heavier than iron, many of which later made their way to planets, were nuclear reactions in supernova explosions.
Past hypothesis
But this hypothesis has passed. Now, scientists think, if you have a gold ring, the atoms are likely to have been forged from a long-ago kilonova in one short stroke. Fong says, “We believe a lot of our heavy elements come from these neutron star mergers.”
The launch of NASA’s James Webb Space Telescope in October 2021 will be the next step. He says the instrument will be sensitive enough that if there is another burst like GRB 200522A. Not only will he be able to observe its afterglow, but he will also be able to obtain a spectrum of it, identifying the unique elements generated in the kilonova.
Meanwhile, Fong’s team report is expected to be published in The Astrophysical Journal and now available on pre-print arXiv.
READ ALSO: Scientists say Jupiter’s frozen moon Europa “glows in the dark” due to radiation
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