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Magnetars are terrifying.
Fast spinning neutron stars with gravity a billion times the magnetic and Earth fields quadrillion times more powerful than that of Earth, every thing about them scares me. If you get too close, it’s hard to know which part of them is the scariest: the tides tear you to pieces, the fierce heat vaporizing you, the magnetic field tearing your atoms apart, or the intense gravity crushing you into pieces. a thin paste of a high atom. .
They can also detonate explosions of energy so powerful that they can physically affect our planet halfway through the galaxy. This did happen in 2004, so I’m not kidding when I say it’s in our best interests to understand them.
For example: we don’t know exactly how they are formed. This could happen when a massive star explodes and the nucleus collapses into an ultra-dense neutron star. Or maybe they were born when two relatively light white dwarfs merge.
But it’s also possible that they are born when two previously formed neutron stars collide. Normally this would create a black hole, but if the two neutron stars have a lower mass than usual, they might be able to avoid this fate.
What would be this look like?
On May 22, 2020, the orbiting Swift satellite detected a bright flash of gamma rays. Locked on impulse, he quickly observed this spot in the sky with his x-ray, ultraviolet and optical telescopes. At the same time, he sent an alert to astronomers on Earth below, saying he had found a gamma-ray burst (or GRB) – designated GRB200522A, given the date.
Gamma rays are the most energetic form of light, and their bursts can come from a variety of objects. But this one lasted less than a second, so that’s what we call a short gamma-ray burst – I know, lame name, but it’s descriptive – that usually happens when two neutron stars collide.
Swift launched in 2004 and has seen a lot of these short bursts. But this one got weird.
Follow-up observations revealed that GRB200522A occurred in a small galaxy producing stars, and that light took 5.5 billion years to reach Earth. So that’s more than a third of the way through the observable Universe! Surprisingly, it’s about equal for the course; most GRBs are observed in distant galaxies. And 70% of all short GRBs occur in galaxies like this.
It was what happened next that was so strange.
When two neutron stars collide, the resulting explosion expels many extremely hot extremely dense material to extremely high speed. Strong magnetic fields concentrate this material into two beams, powerful cones of matter and radiation exploding up and down from the collision. This substance slams into the material around the crash, making it glow as well.
The expelled matter is so hot that it undergoes a fusion, creating what is called r-process elements: gold, platinum, strontium, etc. This fusion releases even more energy, so that the material heats up and shines even more. The energy released in this kind of event is more powerful than a nova, but less than a supernova. Since this is about a thousand times more than a nova, we call it a Kilonova.
Normally, these glow in the infrared. Astronomers therefore pointed the Hubble Space Telescope at GRB200522A and received a shock: the glow in the infrared was easily 10 times which is generally seen from a kilonova. It’s really weird.
In addition, the X-rays and radio emissions also attenuated in a strange way, unlike what is usually seen in a short gamma-ray burst. To top it off, models have shown that in order for this GRB to function like a normal GRB, the exploded jets would have to be unusually wide cones, wider than ever in previous GRBs.
It was clearly no ordinary event. Too weak for a gamma-ray burst, but the afterglow of GRB200522A was much more powerful than a regular kilonova… as if something was left behind adding energy to the material.
A black hole can’t do that. But a magnetar can.
And that’s what astronomers think happened here.
So here’s the story they put together:
Long ago, two massive stars orbiting each other. Over time, one exploded, leaving behind a neutron star, and then the second did the same. Both neutron stars were probably light for their type. Over the next few billion years, they slowly spun together, until, in a cataclysmic event, they collide and merge. A huge explosion ensued, detonating an incredibly dense material, which fused to form elements of r-process: the kilonova.
Left behind was not a black hole but rather a magnetar, a massive single neutron star with extremely powerful magnetism. As it spun rapidly, its extremely strong magnetic field transferred energy to the material around it, making it glow much brighter than if a black hole had formed.
5.5 billion years later, in May 2020, astronomers watch in awe of realizing what they saw.
Magnetars are rare, with only about half a dozen known in our galaxy. But they’re believed to be the engines of mysterious Rapid Radio Bursts (FRBs), brief pulses of intense radio energy that until recently baffled astronomers as to their origin. One of these was seen from a known Milky Way magnetar, so they are likely the source of at least a few FRBs. And they can also send superfluous ones, like the one that hit us in 2004.
Although rare in a galaxy, there are a lot of galaxies, so we see their shenanigans quite often. If GRB200522A was in fact the birth cry of a powerful magnetar, it will be the first ever, and a breakthrough in the understanding of these amazing objects.
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