Astronomers link ‘starquakes’ to mysterious radio signals from space | ultragr

Starquake Art Concept
Starquake Concept Art

Fast radio bursts (FRBs), intense bursts of radio energy, are a perplexing astronomical mystery. Recent research from the University of Tokyo has found similarities between FRBs and earthquakes, suggesting they could be caused by “stellar shocks” on neutron stars. These findings could reshape our understanding of earthquakes, high-density matter, and nuclear physics.

University of Tokyo research links fast radio bursts (FRBs) to “stellar shocks” in neutron stars, offering new insights into earthquakes and nuclear physics.

Fast radio bursts, or FRBs, are an astronomical mystery, their exact cause and origin still unconfirmed. These intense bursts of radio energy are invisible to the human eye, but clearly visible in radio telescopes. Previous studies have noted broad similarities between the energy distribution of repeated FRBs and that of earthquakes and solar flares.

However, new research at the University of Tokyo looked at the timing and energy of FRBs and found distinct differences between FRBs and solar flares, but some notable similarities between FRBs and earthquakes. This supports the theory that FRBs are caused by “stellar shocks” on the surface of neutron stars. This discovery could help us better understand earthquakes, the behavior of high-density matter, and aspects of nuclear physics.

Chinese telescope FAST

China’s Five Hundred Meter Spherical Radio Telescope (FAST). The FRB data were provided by the Five Hundred Meter 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 subsequently decommissioned in 2020. Credit: Bojun Wang, Jinchen Jiang & Qisheng Cui

The enigma of the FRB

The vastness of space hides many mysteries. While some people dream of boldly going where no one has gone before, there is much we can learn from the comforts of Earth. Thanks to technological advances, we can explore the surface Marswonder Saturn‘s rings and pick up mysterious signals from deep space. Fast radio bursts are extremely powerful, bright bursts of energy that are visible on radio waves.

These bursts were first discovered in 2007 and can travel billions of light-years, but usually last only thousandths of a second. It is estimated that up to 10,000 FRBs could happen every day if we could observe the entire sky. While the sources of most of the flares detected so far appear to emit a one-time event, there are about 50 FRB sources that emit flares repeatedly.

Japan earthquake map

Earthquake data was taken from Japan’s Kanto region (including Tokyo and Narita) and Izumo in the Chugoku region (north of Hiroshima). Black dots represent the epicenters of earthquakes recorded between 6 May 2010 and 31 December 2012. Credit: ©2023 T. Totani & Y. Tsuzuki

Theories behind the cause of FRBs

The cause of FRBs is unknown, but some ideas have been put forward, including that they may even be of alien origin. Currently, however, the prevailing theory is that at least some FRBs are emitted by neutron stars. These stars form when a supergiant star collapses from eight times the mass of our Sun (on average) into a superdense core just 20-40 kilometers in diameter. Magnetars are neutron stars with extremely strong magnetic fields and have been observed to emit FRBs.

“Theoretically, the surface of the magnetar could experience a stellar earthquake, a release of energy similar to earthquakes on Earth,” said Professor Tomonori Totani of the Graduate School of Science’s Department of Astronomy. “Recent observational advances have led to the detection of thousands of additional FRBs, so we took the opportunity to compare the now large statistical datasets available for FRBs with data from earthquakes and solar flares to explore possible similarities.”

Comparison of FRBs and Earthquakes

The researchers analyzed the time and energy distributions of FRBs and earthquakes, and by plotting the probability of an aftershock as a function of time lag, they found that the two are very similar. Credit: ©2023 T. Totani & Y. Tsuzuki

Statistical analysis and findings

So far, FRB statistical analysis has focused on the distribution of waiting times between two consecutive 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 might exist between other bursts. So the team set out to calculate the correlation across two-dimensional space and analyzed the emission time and energy of nearly 7,000 flashes from three different repeater FRB sources. They then used the same method to examine the temporal and energy correlation of earthquakes (using data from Japan) and solar flares (using records from Hinode international mission to study the sun) and compared the results of all three phenomena.

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

Totani explained, “The results show remarkable similarities between FRBs and earthquakes in the following ways: First, the aftershock probability of a single event is 10–50%; second, the frequency of occurrence of aftershocks decreases with time, as a power of time; third, the rate of aftershocks is always constant, even when FRB (median rate) earthquake activity varies significantly; and fourth, there is no correlation between the energies of the main discharge and its after discharge.’

This strongly suggests the existence of a solid crust on the surface of neutron stars, and that stellar shocks that suddenly occur on these crusts release huge amounts of energy that we see as FRBs. The team plans to continue analyzing new FRB data to verify that the similarities they found are universal.

“By studying stellar quakes on distant ultradense stars, which are a completely different environment than Earth, we can gain new insights into earthquakes,” Totani said. “Interior and neutron star is the densest place in the universe, comparable to the interior of an atomic nucleus. Stellar tremors in neutron stars have opened up new insights into very 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, 11 Oct 2023, Monthly Notices of the Royal Astronomical Society.
DOI: 10.1093/mnras/stad2532

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