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Two neutron stars snapped together away from Earth. The energy of their collision illuminated their corner of the sky with a brief flash of gamma radiation, followed by a softer, longer lasting glow on electromagnetic spectrum. Looking into this fading light, the researchers spotted a infrared signal – the very first recorded signature, they think, of a newborn cosmic juggernaut, a magnetar.
A magnetar is a neutron star with an unusually strong magnetic field. Astronomers have spotted magnetars elsewhere in the universe, but they have never seen one emerge. This time, researchers suspected they spotted a newborn magnetar because of an unusual pattern of blinking light. First, there was a short ultra-bright burst of gamma radiation (GRB). Then there was a bright, long-lasting ‘kilonova’, a telltale sign of the collision of neutron stars. And that glow was much brighter than usual, suggesting a phenomenon astronomers had never seen before.
To detect neutron star collisions, scientists are looking for both short GRBs and more durable light sources from the collision.
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Under normal circumstances, said Wen-fai Fong, a Northwestern University astrophysicist who led the research, the glow left by a neutron star collision has two parts: There is “afterglow.” short-lived, lasting a few days and resulting from matter moving away from the collision and slamming at high speed in the dust and gas between the stars. And then there is the “kilonova” glow from the agitated particles swirling around the collision site.
The recent event, called GRB 200522A, had a visible kilonova, but something was different.
Scientists know from their models and previous observations how bright a kilonova should be. GRB 200522A was much brighter, especially in the infrared portion of the electromagnetic spectrum.
“I can count on my hands the number of kilonovas that have been discovered from short gamma-ray bursts,” Fong told Live Science. “But it was 10 times brighter than any of them.”
To explain why the kilonova was so bright, the researchers had to determine what new ingredient was present as a result of the neutron star collision.
“We settled on a very large magnetar,” Fong said.
Like a whirling figure skater bringing his arms closer to his body, the two orbiting neutron stars combined to form a faster spinning magnetar. Its powerful magnetic fields acted like the blades of a blender, stirring the already energized kilonova particles, making them even brighter.
There are also other explanations, according to the researchers.
One possibility is a “reverse shock”. Two waves of rapid afterglow particles could have shattered into each other. If the conditions were right, this accident could mimic a newborn magnetar. Likewise, some unexpected decaying radioactive particles in the kilonova could have made GRB 200522A brighter. But Fong said both of these scenarios were unlikely.
Assuming it is a magnetar, Fong said, future observations should reveal radio remote site broadcasts. And one day, the not yet launched James Webb Space Telescope should be able to scan the short GRB sites further, revealing still unseen details of these collisions.
The article describing the work of Fong and his colleagues was published today (November 12) in The Astrophysical Journal.
Originally posted on Live Science.
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