Mysterious flashes of radio waves from space might be caused by interstellar asteroids and comets crashing into neutron stars.
Astronomers detected the first fast radio burst (FRB) in 2007, and several thousand have since been found. They are thought to come from neutron stars, the ultra-dense cores left behind after some stars explode as supernovae, but exactly what causes them is unclear.
The favoured explanation for FRBs is that they come from twisted and powerful magnetic fields snapping together around magnetars, highly magnetised neutron stars.
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at the University of Toronto and his colleagues propose a different solution 鈥� interstellar objects such as asteroids and comets hitting neutron stars.
Solar systems like our own are thought to eject interstellar objects at various points in their lives. Two such objects have been seen drifting through our solar system to date, 鈥極umuamua in 2017 and Comet Borisov in 2019.
Based on those two objects, astronomers have previously calculated there are 10 trillion trillion trillion interstellar asteroids and comets drifting through the Milky Way. When combined with the 1 billion known neutron stars in our galaxy, that would suggest a rate of one collision every 10 million years per neutron star, Pham and his colleagues calculated. That is consistent with the rate of FRBs observed across all galaxies.
As the objects hit the neutron star鈥檚 magnetic field, they would be vaporised in a millisecond, turning into plasma and 鈥渟ped up to close to the speed of light鈥�, says Pham. 鈥淭his ball of plasma is fired along the magnetic field and creates a beam of radiation that might produce an FRB.鈥�
at Queen鈥檚 University Belfast, UK, says it is a 鈥渘eat idea鈥� that we might be able to test by observing the rate of FRBs over the history of the universe. When we look at very distant galaxies, the light reaching us left those galaxies billions of years ago, so we are seeing further back in time. The number of interstellar objects in a galaxy should grow over time, meaning that as you look further back in time, the number of FRBs should decrease, says Fitzsimmons.
The process could account for some FRBs but not all of them, particularly not repeating FRBs that can methodically repeat for months. Each collision would be 鈥渁n inherently random event鈥�, says Pham. That means there would still be other FRB-producing mechanisms taking place. 鈥淲e should not be trying to find a single model that explains them all,鈥� says at the University of Amsterdam in the Netherlands. 鈥淭here鈥檚 a diversity in the types of bursts we see.鈥�
If the interstellar object idea is correct, Pham says we could use this knowledge to probe the nature of some of these objects. 鈥淚f you can say which events are attributed to this mechanism, you can infer the size of these rocks and their tensile strength, which can tell you a lot about how they were formed,鈥� he says.
arXiv
