[Music throughout] A high-energy
outburst seen in April 2020 confirmed the surprising range
of supermagnetized objects called magnetars.
This blast of X-rays and gamma rays triggered instruments on several spacecraft.
The eruption was over in the blink of an eye and originated
from a galaxy about 11 million light-years away.
Magnetars are part of the family of compact objects known as neutron stars,
the crushed, leftover cores of exploded stars.
What makes magnetars special are their incredibly strong
magnetic fields — up to 1,000 times stronger than a typical neutron
star’s. Sudden changes to this ultrastrong field are thought
to drive brief, enormously powerful outbursts called giant flares.
One giant flare in our own galaxy affected Earth’s upper
atmosphere — from 28,000 light-years away.
On April 15th, detectors on NASA’s
Fermi, Swift, Mars Odyssey and Wind missions, as well as
on the European Space Agency’s INTEGRAL satellite, picked up a
rapid surge of X-rays and gamma rays. Using the arrival times of
the signal at different spacecraft, astronomers pinned the burst to
NGC 253, a bright, nearby galaxy.
From start to finish, the event lasted 140 milliseconds — as
fast as a finger snap. Astronomers see
gamma-ray bursts, or GRBs, almost every day. We know that
at least some of the shortest GRBs come from merging neutron stars
more than 100 million light-years away. The April blast
initially looked similar to these events. But a GRB located
in our own galactic neighborhood should have appeared much brighter.
As astronomers explored this new burst in detail, they
found it looked less like a short GRB and more like a magnetar
giant flare. Astronomers have recorded two such
flares inside our own galaxy and a third in a satellite galaxy.
All of these bursts displayed a spikey tail as they faded out.
The spikes form as the flare's hot spot spins in and out of view,
like a lighthouse beam. Current instruments can’t detect
this feature in flares located at great distances, but other
characteristics, such as their extremely fast rise in brightness, are
unmatched by short GRBs. This fueled
astronomers’ growing suspicions that short GRBs associated with galaxies
in our neighborhood might really be magnetar giant flares.
Now, the precise localization of the 2020 event
to the disk of the Sculptor galaxy has unmasked them at last.
Astronomers suspect that a few percent of observed short GRBs
may in fact be giant flares — high-powered eruptions
in our galactic back yard produced by the strongest
magnets in the cosmos.
NASA