Mysterious fast radio bursts (FRBs) have been puzzling astronomers since their discovery in 2007.
The cause and origin of these ultra-bright bursts of radio waves is unclear – two prevailing theories are that they either come from solar flares, or from “starquakes” — tremors in super-dense neutron stars.
A pair of Japanese researchers have added weight to the starquake theory, saying the patterns of FRBs resemble those of earthquakes on Earth.
They’ve published their study in Monthly Notices of the Royal Astronomical Society.
FRBs have been observed from “magnetars”: neutron stars with extremely strong magnetic fields.
“It was theoretically considered that the surface of a magnetar could be experiencing a starquake, an energy release similar to earthquakes on Earth,” says co-author Professor Tomonori Totani from the Department of Astronomy at the University of Tokyo.
“Recent observational advances have led to the detection of thousands more FRBs, so we took the opportunity to compare the now large statistical data sets available for FRBs with data from earthquakes and solar flares, to explore possible similarities.”
Totani, along with graduate student Yuya Tsuzuki examined the time and emission energy of 7,000 FRBs, coming from 3 different repeat sources. Then, they used the same analysis on earthquakes and solar flares.
Totani says there are notable similarities between FRBs and earthquakes in 4 ways.
“First, the probability of an aftershock occurring for a single event is 10-50%; second, the aftershock occurrence rate decreases with time; third, the aftershock rate is always constant even if the FRB-earthquake activity (mean rate) changes significantly; and fourth, there is no correlation between the energies of the main shock and its aftershock.”
The researchers believe that this means there’s a solid crust on the surface of neutron stars, and starquakes on these crusts emit huge bursts of energy that our telescopes pick up as FRBs.
“By studying starquakes on distant ultradense stars, which are completely different environments from Earth, we may gain new insights into earthquakes,” says Totani.
“The interior of a neutron star is the densest place in the universe, comparable to that of the interior of an atomic nucleus. Starquakes in neutron stars have opened up the possibility of gaining new insights into very high-density matter and the fundamental laws of nuclear physics.”