Astronomers link ‘starquakes’ to mysterious radio signals from space

Research from the University of Tokyo links fast radio bursts (FRBs) to “starquakes” on neutron stars, providing new insights into earthquakes and nuclear physics.

Fast radio bursts, or FRBs, are an astronomical mystery, and their cause and origins remain uncertain. These intense bursts of radio energy are invisible to the human eye, but appear brightly on radio telescopes. Previous studies have observed broad similarities between the energy distribution of recurring fast radio bursts and the energy distribution of earthquakes and solar flares.

However, new research at the University of Tokyo has looked at the time and energy of FRBs and found clear differences between FRBs and solar flares, but there are many notable similarities between FRBs and earthquakes. This supports the theory that FRBs result from “starquakes” on the surface of neutron stars. This discovery could help us better understand earthquakes, the behavior of high-density materials, and aspects of nuclear physics.

China’s Five-Hundred-Meter Aperture Radio Telescope (FAST). The FRB data were provided by the Five Hundred Meter Aperture Spherical Telescope (FAST) in China and the Arecibo Telescope in Puerto Rico, two of the largest single-dish telescopes in the world. Unfortunately, the Arecibo telescope was damaged and decommissioned later in 2020. Source: Bojun Wang, Jinchen Jiang & Qisheng Cui

The mystery of fast radio bursts (FRBs).

The vastness of space holds many mysteries. While some people dream of boldly going somewhere no one has gone before, there is much we can learn from the comfort of the land. Thanks to technological advances, we can explore the surface MarsWonders of Saturnrings, picking up mysterious signals from deep space. Fast radio bursts are extremely powerful, bright bursts of energy that can be seen on radio waves.

First discovered in 2007, these bursts can travel billions of light-years but typically last only milliseconds. It is estimated that up to 10,000 FRBs could occur every day if we could observe the entire sky. While most burst sources discovered so far appear to emit a one-time event, there are about 50 fast burst sources that emit bursts repeatedly.

Seismic data were taken from the Kanto region of Japan (including Tokyo and Narita) and Izumo in the Chugoku region (north of Hiroshima). The black dots represent the epicenters of earthquakes recorded between May 6, 2010 and December 31, 2012. Source: ©2023 T. Totani & Y. Tsuzuki

Theories behind the cause of fast radio bursts

Why fast radio bursts occur is unknown, but some ideas have been put forward, including that they may be alien in origin. However, the current prevailing theory is that at least some fast radio bursts are emitted by neutron stars. These stars form when a giant star collapses, ranging in mass from eight times the mass of our Sun (on average) to an ultra-dense core just 20 to 40 kilometers across. Magnetars are neutron stars with extremely strong magnetic fields, and have been observed to emit FRBs.

“Theoretically, it was thought that the surface of a magnetar could experience a starquake, an energy release similar to earthquakes on Earth,” said Professor Tomonori Totani from the Department of Astronomy at the Graduate School of Science. “Recent observational advances have led to the discovery of thousands more fast radio bursts, so we took the opportunity to compare the large statistical datasets currently available for fast radio bursts with data from earthquakes and solar flares, to explore potential similarities.”

The researchers analyzed the time and energy distribution of fast radio bursts and seismic events, and by plotting the probability of aftershocks as a function of the time difference, they found that the two are very similar. Credit: ©2023 T. Totani & Y. Tsuzuki

Statistical analysis and results

Until now, statistical analysis of fast radio bursts has focused on the distribution of waiting times between two successive bursts. However, Totani and co-author Yuya Tsuzuki, a graduate student in the same department, point out that calculating only the waiting time distribution does not take into account correlations that may exist across other bursts. So the team decided to calculate the correlation across 2D space, analyzing the time and energy of the emission of nearly 7,000 bursts from three different fast radio burst sources. They then applied the same method to examine the relationship between earthquakes, time and energy (using data from Japan) and solar flares (using records from… Hinode International Mission to Study the Sun) and compare the results of the three phenomena.

Totani and Tsuzuki were surprised that, unlike other studies, their analysis showed a striking similarity between FRBs and seismic data, but a distinct difference between FRBs and solar flares.

“The results show remarkable similarities between fast radio bursts and earthquakes in the following ways: first, the probability of an aftershock for a single event is 10-50%; second, the incidence of aftershocks decreases over time, as the force of time; third, the rate of aftershocks is Always constant even if the FRB earthquake activity (average rate) changes significantly; and fourth, there is no relationship between the energies of the main shock and its aftershocks.

This strongly suggests that there is a solid crust on the surface of neutron stars, and that starquakes that occur suddenly on these crusts release huge amounts of energy that we see as FRBs. The team plans to continue analyzing new data on fast radio bursts, to verify that the similarities they have found are universal.

“By studying stellar quakes on distant, ultra-dense stars, which are very different environments from Earth, we may gain new insights into earthquakes,” Totani said. “Interior A Neutron star It is the densest place in the universe, compared to the interior of the atomic nucleus. Stellar quakes in neutron stars have opened the possibility of gaining new insights into high-density matter and the fundamental laws of nuclear physics.

Reference: “Fast radio bursts trigger earthquake-like aftershocks, but not solar flares” by Tomonori Totani and Yuya Tsuzuki, October 11, 2023, Monthly Notices of the Royal Astronomical Society.
doi: 10.1093/manras/stad2532