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For over a decade, the phenomenon known as fast radio bursts has excited and bewildered astronomers. These extraordinarily bright but extremely short bursts of radio waves – lasting a few milliseconds – reach Earth from galaxies billions of light years away.
In April 2020, one of the explosions was first detected from inside our own galaxy, the Milky Way, by CHIME and STARE2 radio telescopes. The unexpected glow was traced to a previously known source just 25,000 light-years from Earth in the constellation of Vulpecula, the Fox, and scientists from around the world have coordinated their efforts to track the discovery.
In May, a team of scientists led by Franz Kirsten (Chalmers) aimed four of Europe’s best radio telescopes, known as SGR 1935 + 2154, at the source. Their results are published today in an article in the journal Nature Astronomy.
‘We didn’t know what to expect. Our radio telescopes had only rarely been able to see fast radio bursts, and this source seemed to be doing something entirely new. We were hoping to be surprised! ‘Said Mark Snelders, team member of the Anton Pannekoek Institute of Astronomy, University of Amsterdam.
Radio telescopes, one dish each in the Netherlands and Poland and two at the Onsala Space Observatory in Sweden, monitored the source every night for more than four weeks after the first flash was discovered, for a total of 522 hours of observation.
On the evening of May 24, the team got the surprise they were looking for. At 11:19 pm local time, the Westerbork telescope in the Netherlands, the only one of the group in service, caught a dramatic and unexpected signal: two short bursts, each one millisecond long but 1.4 seconds apart.
Kenzie Nimmo, an astronomer at the Anton Pannekoek Institute for Astronomy and ASTRON, is a member of the team.
“We clearly saw two volleys, extremely close in time. Like the flash seen from the same source on April 28, this one looked just like the fast radio bursts we had seen from the distant universe, only fainter. The two explosions we detected on May 24 were even weaker than that, ‘he said.
This was strong new evidence linking fast radio bursts with magnetars, scientists thought. As more distant sources of fast radio bursts, SGR 1935 + 2154 appeared to produce bursts at random intervals and over a huge range of brightness.
“The brightest flashes of this magnetar are at least ten million times brighter than the faintest ones. We asked ourselves, could this also be true for fast radio burst sources outside our own galaxy? If so, then the universe’s magnetars are creating beams of radio waves that could traverse the cosmos all the time – and many of these could be within reach of small telescopes like ours, ” the team member said. Jason Hessels (Anton Pannekoek Institute for Astronomy and ASTRON, The Netherlands).
Neutron stars are the tiny and extremely dense remnants left over when a short-lived star over eight times the mass of the Sun explodes as a supernova. For 50 years, astronomers have studied pulsars, neutron stars that emit pulses of radio waves and other radiation with clock-like regularity. All pulsars are believed to have strong magnetic fields, but magnetars are the strongest magnets known in the universe, each with a magnetic field hundreds of trillions times stronger than that of the Sun.
In the future, the team aims to keep radio telescopes monitoring SGR 1935 + 2154 and other nearby magnetars, in hopes of pinpointing how these extreme stars actually produce their brief bursts of radiation.
Scientists have presented many ideas about the speed of generation of radio bursts. Franz Kirsten, astronomer at the Onsala Space Observatory, Chalmers, who led the project, expects the rapid pace in understanding the physics behind fast radio bursts to continue.
“The fireworks from this fantastic nearby magnetar have given us exciting clues as to how quickly radio bursts could be generated. The explosions we detected on May 24 could indicate a dramatic disturbance in the star’s magnetosphere near its surface. Other possible explanations, such as shock waves further away from the magnetar, seem less likely, but I’d be glad to be proven wrong. Whatever the answers, we can expect new measurements and new surprises in the months and years to come, “he said.
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