Astrophysicists have tracked the location of the source of the recently detected fast radio burst FRB 20200120E. It turned out to be 11.7 million light years away, making it the closest extragalactic radio burst. Moreover, it is associated not with a magnetar, as previously assumed, but with a globular cluster of stars – an unusual place for the origin of fast radio bursts. The research results are published on the arXiv.org preprint server.
Fast Radio Bursts (FRBs) are extremely bright and short radio pulses that last for a fraction of a second and during this time eject into space energy equivalent to that emitted by the Sun over several tens of thousands of years. They were first discovered in 2007, but their nature is still a mystery.
Last year, scientists managed to link several FRBs to magnetars – compact, furiously rotating neutron stars with a very strong magnetic field and powerful emissions of gamma and X-rays. But the fast radio burst FRB 20200120E discovered in 2021 brought new surprises.
Astronomers have tracked its location to a globular cluster of stars in spiral galaxy M81, located 11.7 million light years away, 40 times closer than any other known extragalactic FRB. Since such globular clusters contain old stellar populations, and magnetars cannot be there, scientists at first questioned the correctness of determining the source of the radio burst.
In a new study, the authors argue that FRB 20200120E really comes from the globular cluster M81, that is, the mechanism for the formation of fast radio bursts is broader than previously assumed.
“Because such globular clusters contain old stellar populations, this association challenges FRB models that use core-collapsing supernova magnetars as the source of FRB radiation,” the authors write.
They offer an alternative option for the formation of fast radio bursts. According to the authors, the source of FRB may not be a magnetar at all, but an X-ray binary system with a low mass, such as a white dwarf and a neutron star or a neutron star and an exoplanet. Because globular clusters are so dense, stars in them can interact and even collide with each other, creating objects such as low-mass X-ray binaries and pulsars.
From time to time, rapidly rotating neutron stars known as millisecond pulsars are discovered in globular clusters. A white dwarf interacting with another star and accreting it can gain enough mass to collapse into a neutron star. Or two white dwarfs can merge in the same way. Another option is an accreting black hole.
The researchers note that so far they do not have unequivocal evidence in favor of this or that option. The situation is complicated by the fact that in this case the fast radio burst was not accompanied by X-ray or gamma-ray activity, which is usually observed together with FRB. Scientists are inclined to believe that the source of FRB 20200120E was a young, highly magnetized neutron star, formed either as a result of the collapse of a white dwarf caused by accretion, or as a result of the merger of compact stars in a binary system.