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NASA / ESA / D. Participant (STScI)
It seems, two neutron stars don’t essentially make a black gap.
Neutron star collisions are seemingly on the coronary heart of brief gamma-ray bursts (GRBs), flashes of gamma radiation that final lower than two seconds however carry extra energy than the Solar will produce in its lifetime. Basic math means that when two neutron stars come collectively on this approach, they must have sufficient mass to make a black gap — supplied they don’t lose an excessive amount of materials within the technique of merging.
Observing the glow that follows these explosive mergers is tough, however with the assistance of the Hubble House Telescope, astronomers have caught the afterglow of 1 such burst, GRB 200522A. Its fading radiation carries an essential message: Violent as these blasts is perhaps, they’re not essentially cataclysmic. At the very least on this case, a extremely magnetized neutron star, or magnetar, seems to have survived the occasion.
Wen-Fai Fong (Northwestern College) and colleagues have posted observations of this GRB on the arXiv preprint server, and the examine will seem within the Astrophysical Journal later this 12 months.
An Odd Burst
NASA’s Neil Gehrels Swift Observatory first detected the burst after the radiation had traveled for five.47 billion years to Earth. Fong’s group noticed it once more with Hubble House Telescope and a large number of different ground-based observatories following the preliminary GRB. However when it got here time to grasp the relation between radiation throughout the electromagnetic spectrum — from radio to infrared to X-rays — the group at first couldn’t make sense of what they have been seeing.
After two neutron stars collide, producing the preliminary burst of gamma-rays, there’s an afterglow of emission that comes from the shock wave that follows. Because the shock wave blasts out, electrons from the exploding plasma spiral across the shock’s magnetic fields. Identified to astronomers as a kilonova, this emission explains many of the afterglow from different GRBs. However it didn’t work for this one — the infrared emission was 10 occasions brighter than anticipated.
“The truth that we see this infrared emission, and that it’s so brilliant, exhibits that brief gamma-ray bursts certainly type from neutron star collisions,” says group member Edo Berger (Heart for Astrophysics, Harvard & Smithsonian), “however surprisingly the aftermath of the collision might not be a black gap, however reasonably seemingly a magnetar.”
A Magnetar Survives
The group actually contemplate two situations: One is that the neutron star collision birthed a magnetar. The second is that the collision produced a black gap, accompanied by a jet of plasma touring at relativistic pace away from the collision with a surprisingly vast angle.
“In my view, the magnetar situation supplies a extra simple rationalization for the observations,” says Maria Grazia Bernardini (Nationwide Institute of Astrophysics, Rome), a GRB professional who was not concerned within the examine. It’s unlikely, she provides, relativistic jet would spray plasma so broadly; such jets are usually fairly slim. A jet additionally wouldn’t make the correct amount of X-rays, Fong’s group notes.
“GRB 200522A is a outstanding instance of how brief GRB afterglows can nonetheless shock and puzzle us 15 years after their discovery,” Bernardini says.
If a magnetar survived the collision, it’s going to nonetheless be round for a very long time to come back. Inside a couple of years, Fong and his colleagues write, the magnetized remnant ought to produce observable radio emission.
“If detected, this is able to not solely break the degeneracy between the 2 potential explanations on this particular case,” Bernardini says, “however it will present the long-sought smoking gun of the magnetar situation, and the primary direct proof of a secure magnetar related to a GRB.”
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