Fast Radio Bursts are one of the top mysteries facing astronomy today. These energetic events consist of huge bursts of radio waves that last very little time. Astronomers have detected a few repeat events that were observed in nature. There are many theories about the cause of the bursts, ranging from rotating neutron stars to extraterrestrials.
Since the first event was detected fifteen years ago, improvements in our instruments and dedicated array have led to many more detections. An international team of astronomy recently made high-precision measurements of a repeating FRB located in the spiral galaxy M 81. The team's findings have helped answer some questions.
The international team was made up of researchers from the Netherlands Institute for Radio Astronomy, the Onsala Space Observatory, the Max Planck Institute for Radio Astronomy, and the Ventspil.
Their findings were described in two papers published this week. The studies were led by two people, one of which is a graduate student at the University of Amsterdam.
In their papers, the team describes how they set out to make high-precision measurements of a repeating FRB discovered in January 2020. To study the source with the highest possible resolution and sensitivity, the team combined measurements from multiple instruments in the European VLBI Network.
The Karl G. Jansky Very Large Array (VLA) in New Mexico was one of the powerful radio telescopes. They realized the repeating FRB came from the nearby spiral galaxy M 81. This event is the closest to date and is located about 12 million light-years away from Earth. In a recent press release, it was explained that as Kirsten explained.
“We wanted to look for clues to the bursts’ origins. Using many radio telescopes together, we knew we could pinpoint the source’s location [in] the sky with extreme precision. That gives the opportunity to see what the local neighborhood of a fast radio burst looks like.
The team traced the FRB to the outskirts of the galaxy and realized that it was coming from a dense cluster of very old stars. Many FRBs are surrounded by young, massive, short-lived stars and many times the mass of our Sun. These stars end their lives as white dwarfs known as magnetars.
It is amazing to find fast radio bursts from a cluster. Fast radio bursts have been found in places where stars are younger. Astronomers believe that young stars undergoing collapse to become magnetars are the reason for FRBs. A lot of research has been done in recent years.
The findings suggest that they may be linked to magnetars that formed when a white dwarf became massive enough to collapse under its own weight. The professor with the University of Amsterdam and ASTRON is a member of the team.
“We expect magnetars to be shiny and new, and definitely not surrounded by old stars. So if what we’re looking at here really is a magnetar, then it can’t have been formed from a young star exploding. There has to be another way.”
Some stars in a globular cluster get close to one another to collect material from the other. When one star is no longer in its main sequence, it can become a Red Giant. The companion will begin to suck material from the Red Dwarf's outer layers.
If one of the white dwarfs can catch enough mass from its companion, it can turn into a denser star called a neutron star.
After looking for additional clues, the astronomer found something that surprised them. Some of the flashes they observed were shorter in duration than they were expected to be. This is similar to what has been seen from a pulsar in the Crab Nebula, a tiny, dense remnant of a supernova explosion that was seen from Earth in 1054CE. Said Nimmo.
“The flashes flickered in brightness within as little as a few tens of nanoseconds. That tells us that they must be coming from a tiny volume in space, smaller than a soccer pitch and perhaps only tens of meters across. Some of the signals we measured are short and extremely powerful, in just the same way as some signals from the Crab pulsar. That suggests that we are indeed seeing a magnetar, but in a place that magnetars haven’t been found before.”
Astronomers will be able to tell if the source is an unusual magnetar, an unusual pulsar, a black hole, or something else entirely by observing this system and others like it. It is clear that the detection of more FRBs is leading to new and unexpected insights into the life cycle of stars.
Further reading: Nature.
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