The hottest topic of 2020 may have been magnetars, and that trend seems to be carrying over to 2021. These Manhattan-sized stars, back in more than a Sun’s worth of mass into a sphere roughly 20 miles across. This, by itself, just makes them dense objects called neutron stars. Add in some of the most powerful magnetic fields in the universe, and now you have a special kind of monster capable of releasing bursts of gamma rays capable of overexposing a camera from half a galaxy away and maybe even further.
On Wednesday, magnetar-studying scientists from around the world came together to present their work at the AAS meeting. These presentations were done over Zoom.
Random fact – the last time I was on a plane was to come home from last year’s AAS meeting.
In work presented by UC Berkeley researcher Kevin Hurley, we got the details on a high energy burst from a magnetar that occurred on April 15, 2020. Here I quote from the release:
Shortly before 4:42 a.m. EDT on that Wednesday, a brief, powerful burst of X-rays and gamma rays swept past Mars, triggering the Russian High Energy Neutron Detector aboard NASA’s Mars Odyssey spacecraft, which has been orbiting the planet since 2001. About 6.6 minutes later, the burst triggered the Russian Konus instrument aboard NASA’s Wind satellite, which orbits a point between Earth and the sun located about 930,000 miles (1.5 million kilometers) away. After another 4.5 seconds, the radiation passed Earth, triggering instruments on NASA’s Fermi Gamma-ray Space Telescope and the European Space Agency’sINTEGRAL satellite.
That burst lasted only 140 milliseconds, but thanks to how it affected so many different instruments, at specifically measured times, scientists were able to figure out where it came from even though no instrument had time to focus on it while it was happening.
Hurley and his collaborator Dimitry Svinkin of the Ioffe Institute were able to pinpoint the source as being in the galaxy NGC 253, which is located 11.4 million light-years away. This distance was actually a good thing. Back in 2004, a burst in our own galaxy overwhelmed all our detectors in a way that allowed us to catch hints at how it flickered, but that didn’t really let us see any details. This new 2020 burst was too far away to have the same effect, and the team could see how the fluctuations were the same, but this time could see the details.
And it is in the details that the awesomeness is hidden.
For about 50 years, astronomers have known that our universe is periodically blasting us with bursts of gamma rays. Our atmosphere keeps us safe, but spacecraft can see these blasts going off in all directions. These blasts come in a couple of different varieties: short ones lasting at most seconds with a fairly smooth profile, shorter ones that flicker a bit super fast, and longer ones. The longer ones are associated with exploding massive stars, the short and smooth ones are from merging, plain, boring neutron stars. The flickering ones, those were a mystery until now.
The distinctive flickering and energy distribution observed in 2004 matches this new 2020 event, and we know that these short flickering bursts are from magnetars and the thinking is that all these rare events are from these tiny magnetars.
I’m not sure how to explain just how powerful these events are. You may have heard that the northern lights or aurora are caused by solar flares. Periodically, we see our sun’s magnetic field lines snap and rearrange in ways that release particles and energy that can put on these amazing shows in our sky.
Magnetars can have magnetic fields trillions of times stronger than the sun. If one of these was nearby in the galaxy, this kind of event could destroy our atmosphere. Luckily, these objects are very rare, and we don’t seem to have any nearby.
The thing I love about this research is it proves once again that the universe is more complex than we give it credit for. Up until a few years ago, astronomers confidently said, there are two kinds of gamma-ray bursts: short and long. Then we realized, as we observed neutron stars merging for the first time, that the short ones didn’t all fit together, and now, we realize there are at least three kinds of gamma-ray bursts. I look forward to the universe doing some even more unusual things that expand this list even further.
“A bright γ-ray flare interpreted as a giant magnetar flare in NGC 253,” D. Svinkin, D. Frederiks, and R. Starr, 2021 January 13, Nature
“Rapid spectral variability of a giant flare from a magnetar in NGC 253,” O.J. Roberts et al., 2021 January 13, Nature
“High-energy emission from a magnetar giant flare in the Sculptor galaxy,” The Fermi-LAT Collaboration, 2021 January 13, Nature Astronomy