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Albert McKeon

Jun 18th 2021

Heavy, Bright Stuff: The First Sighting of a Magnetar Could Unlock Celestial Clues

In space, the death of a big star doesn’t always signify a finale.

The remains of two large stars occasionally produce a magnetar: a showstopper of cosmic activity and a testament to the power of unity. Astronomers might have recently observed such an alliance, although it’s possible the sighting was nothing more than a spectacular light show.

Even if the stars inevitably don’t hold together — or if the observed light turns out to not have been the shaping of a magnetar in the first place — scientists nonetheless hope the event can provide clues about stellar crashes and the workings of astrophysics.

Renewed as a Pulsar or Magnetar

A dying star isn’t just the stuff of songs. In reality, when a massive star reaches its end days and has expended all of its nuclear fuel, it explodes as a supernova. The expiring star’s outer layers erupt, as Astronomy explains, but its core collapses into a dense new object: a neutron star.

Imagine a single atomic nucleus scaled to the size of Chicago. That’s roughly what you’re looking at with a typical neutron star: a force that’s 14 miles across, weighing more than our sun. Some neutron stars, known as pulsars, spin at dizzying speeds as fast as hundreds of times a second, according to Phys.org. A few young neutrons, though, are more movers than shakers and become magnetars. As the name implies, magnetars involve magnetism. They are surrounded by magnetic fields millions of times stronger than any such force found on Earth.

A Spectacular Light Show

In May 2020, NASA’s Neil Gehrels Swift Observatory — with the help of the Hubble Space Telescope, the Very Large Array, W.M. Keck Observatory and the Las Cumbres Observatory Global Telescope network — detected a burst of gamma-ray light.

Soon after, Northwestern University astrophysicist Wen-fai Fong and his colleagues began studying the explosion of light. As with many discoveries in the outer reaches of space, the scientists can’t present their findings with absolute certainty. They can only theorize with the limited evidence on hand — as illustrated by the cautious title of their report in Astrophysical Journal, “A Luminous Kilonova or a Collimated Outflow With a Reverse Shock?”

A kilonova usually coincides with a short gamma-ray burst. The kilonova glows because of the radioactive decay of heavy elements that are ejected during a merger of two compact objects, producing coveted elements such as gold and uranium. This spraying of neutron-rich material is a sight to behold — but one never observed from Earth until the recent viewing. Due to the principles of space and time, what was seen didn’t reflect a recent moment but rather something that happened long ago.

And what a sight it was. The burst of gamma rays unleashed more energy in a half-second than the sun will produce over its entire 10-billion-year lifetime, the astrophysicists told Northwestern Now.

More Observation Needed to Confirm

“When two neutron stars merge, the most common predicted outcome is that they form a heavy neutron star that collapses into a black hole within milliseconds or less,” Fong said in the interview with Northwestern Now. “Our study shows that it’s possible that, for this particular short gamma-ray burst, the heavy object survived. Instead of collapsing into a black hole, it became a magnetar.”

The rapid spinning of the newly formed neutron star might have prevented it from collapsing into itself and becoming a black hole, Fong told Science News. But it also may have succumbed to its own mass and created a black hole that expelled the jet of charged plasma that moved at the speed of light.

If a magnetar was indeed formed — depositing its energy into kilonova material and creating the light show seen last year — within a few years, the ejected material from the explosion will forward light that will appear on radio wavelengths, Fong’s team said. If valid, the observation and study will help to explain how magnetars form.

Fong told Science News that this possible magnetar formation could ultimately shed light on the stability and size of neutron stars.

“We don’t know the maximum mass of neutron stars,” she explained, “but we do know that in most cases, they would collapse into a black hole [after a merger]. If a neutron star did survive, it tells us about under what conditions a neutron star can exist.”

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