Dramatic luminous kilonova is 10 times brighter than predicted

You’ve probably heard of a supernova, when a star reaches the end of its life and explodes in a huge burst of energy. But these aren’t the only dramatic explosions out in space — there are also kilonovas, which occur when two neutron stars or a neutron star and a black hole collide and merge. These epic events throw outbursts of gamma rays and create heavy elements, though there is much we still have to learn about them.

Now, researchers have investigated the most luminous kilonova ever seen, and they think that it could have caused the birth of a massive star called a magnetar.

Artist's conception of short gamma-ray burst 200522A, the result of what scientists have confirmed to be the brightest kilonova ever recorded, at ten times brighter than the next closest observed event.
Artist’s conception of short gamma-ray burst 200522A, the result of what scientists have confirmed to be the brightest kilonova ever recorded, at 10 times brighter than the next closest observed event. NASA, ESA, and D. Player (STScI)

Researchers first observed the burst, called 200522A, on May 22 this year. They estimated the light had traveled for 5.47 billion years to reach us. They then used the Hubble Space Telescope and various ground-based telescopes to observe the phenomenon and found that it had put out 10 times more infrared emission that they expected.

“The Hubble observations were designed to search for infrared emission that results from the creation of heavy elements — like gold, platinum, and uranium — during a neutron star collision, which gives rise to a short gamma-ray burst,” said Edo Berger, an astronomer at the Center for Astrophysics | Harvard & Smithsonian, and principal investigator of the Hubble program. “Surprisingly, we found much brighter infrared emission than we ever expected, suggesting that there was additional energy input from a magnetar that was the remnant of the merger.”

This was unexpected, as previously scientists had believed that when two neutron stars merge, they produce a black hole. But these findings show that the story is more complex, as the gamma-ray burst suggests the birth of a magnetar instead. A magnetar is a type of neutron star with a very powerful magnetic field, which creates a lot of radiation in the form of X-rays and gamma rays.

“Hubble really sealed the deal in the sense that it was the only one to detect infrared light,” explained lead author Wen-fai Fong, an astronomer at Northwestern University in Evanston, Illinois. “Amazingly, Hubble was able to take an image only three days after the burst. You need another observation to prove that there is a fading counterpart associated with the merger, as opposed to a static source. When Hubble looked again at 16 days and 55 days, we knew we had not only nabbed the fading source, but that we had also discovered something very unusual. Hubble’s spectacular resolution was also key in disentangling the host galaxy from the position of the burst and to quantify the amount of light coming from the merger.”

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