Scientists have been puzzled by the origin of fast radio bursts (FRBs), powerful flashes of radio waves that reach Earth from distant galaxies.
A new study suggested that some of these bursts may be caused by violent tremors on the surface of neutron stars, the remnants of massive stars that exploded in supernovas.
What are fast radio bursts and why are they mysterious?
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Fast radio bursts are brief but intense pulses of radio waves that last only a few milliseconds. They were first detected in 2007, and since then, hundreds of them have been observed by radio telescopes around the world.
Some FRBs repeat while others seem to occur only once. They come from extragalactic sources, meaning they travel across billions of light-years to reach us.
The origin and nature of FRBs are still unknown, despite many theories and observations. Some scientists think they are related to solar flares, or eruptions of plasma from the surface of stars.
Others think they are linked to magnetars, a type of neutron star with extremely strong magnetic fields. Magnetars can produce powerful bursts of gamma rays and X-rays, as well as radio waves.
However, not all FRBs can be explained by magnetars. Some FRBs have different patterns and properties that do not match those of known magnetars.
For example, some FRBs have a low dispersion measure, which means they have not traveled through much intergalactic gas or dust.
This suggested that they come from relatively nearby sources, within our galaxy or its vicinity.
A team of researchers from the University of Tokyo has proposed a new explanation for some of these low-dispersion FRBs.
They suggested that they are caused by starquakes or sudden shifts on the surface of neutron stars.
Starquakes can happen when the crust of a neutron star cracks or slips due to stress from its rotation or magnetic field. This can release a large amount of energy in the form of gravitational waves, heat, and electromagnetic radiation.
The researchers compared the energy distribution of repeating FRBs with that of earthquakes on Earth. They found that they have similar patterns, following a power-law distribution.
This means that there are many small events and few large ones and that the frequency of events decreases as their size increases. This is also known as the Gutenberg-Richter law in seismology.
The researchers also calculated the magnitude of starquakes that could produce FRBs within the observed energy range.
They found that they would be comparable to earthquakes with magnitudes between 15 and 18 on the Richter scale. For comparison, the largest earthquake ever recorded on Earth had a magnitude of 9.5.
The researchers concluded that starquakes could be a plausible source of some low-dispersion FRBs, especially those that repeat.
They also suggested that studying FRBs could help us understand earthquakes better, and vice versa.
"By studying another system which we believe also follows the Gutenberg-Richter law, we may learn more about how this law works and where it applies," said co-author Hiroyuki Narihara in a press release. "Additionally if we can find more FRBs associated with starquakes, we may learn more about the internal structure and magnetic fields of neutron stars."
