Researchers have discovered cosmic flashes in a very surprising place in the universe. And that may also point to a very surprising source.
Since the first fast radio bursts were discovered in 2007, astronomers have been trying to get to grips with these puzzling phenomena. Most of the mysterious radio bursts discovered, however, often came from such far-flung corners of the universe that it was difficult to determine exactly what caused them. Until at the end of 2020 researchers suddenly came across fast radio flashes that seemed to come from our own Milky Way. And now researchers have discovered fast radio bursts at an even closer distance from Earth, bringing us one step closer to solving the mystery.
Fast radio bursts are unpredictable, extremely short but huge bursts in space. During these eruptions, a huge amount of energy is released in a short time. Each flash lasts only one-thousandth of a second. Yet each flash emits as much energy as the sun gives off in a day. The first fast radio burst was discovered in 2007. Since then, many more fast radio bursts have been found scattered across the universe. Most are located at great distances from Earth in galaxies billions of light years away. Only a few have been observed closer.
Astronomers tracked the repetitive eruptions using 12 radio telescopes in the European VLBI Network (EVN) at the edge of the nearby spiral galaxy Messier 81 (M81), about 12 million light-years away from Earth. A surprising discovery. Because it is the closest source of fast radio bursts that has been located so far.
In addition, the researchers had not expected fast radio bursts at this location. The location corresponded exactly to the location of a globular cluster, a dense cluster of very old stars. “It’s amazing to find fast radio bursts in a globular cluster,” said researcher Franz Kirsten. “This is a place in space where you only find old stars. Farther in the universe, fast radio bursts have been found in places where stars are much younger.”
Predicted, but never observed
What causes the fast radio bursts? The scientists suspect that the flashes are coming from an object that has been predicted but never seen before. For example, the repetitive outbursts could be traced to a magnetar formed after a white dwarf star collapsed under its own weight.
The suspicion that fast radio flashes are caused by magnetars has been around for some time. A magnetar is a fairly rare type of neutron star: a super-compact remnant of exploded massive stars. But the magnetar that may have caused the current radio bursts is quite unique. Many stars in clusters form binary stars. Some are so close that one star attracts material from the other. Once one of the white dwarfs has captured enough extra mass from its companion, the star ends its life as a neutron star. “That’s rare, but in a cluster of old stars, it’s the easiest way to cause fast radio bursts,” said researcher Mohit Bhardwaj.
Although the study brings us one step closer to unraveling the source of fast radio bursts, it also raises new mysteries at the same time.
Much to the team’s surprise, some of the observed flashes were shorter than expected. “The flashes flickered in brightness within just tens of nanoseconds,” said study researcher Kenzie Nimmo. “That means they must come from a minuscule volume in space, smaller than a football field and perhaps only tens of meters in diameter.”
It means there’s still plenty of work to do to better understand the mysterious and bizarre phenomena. Future observations of the globular cluster in M81, for example, should determine whether the source is really an unusual magnetar or something else, such as an unusual pulsar or a black hole orbiting a massive star. “These fast radio bursts seem to give us new and unexpected insights into how stars live and die,” concludes Nimmo. “Like supernovas, they could tell us more about the life course of stars in the universe.”
†Cosmic flashes discovered in a surprising location in space” – Dutch Research School for Astronomy (NOVA)
Image at the top of this article: Daniëlle Futselaar