There’s new evidence that the mysterious flashes of radio light that blaze out across the Universe are caused by the massive shudders of dead stars.
An analysis of thousands of flashes from three repeating fast radio burst sources has revealed a similarity – not to solar flares as has been proposed – but to earthquakes.
This similarity, according to astronomers Tomonori Totani and Yuya Tsuzuki of the University of Tokyo, bolsters support for a starquake source for these colossal outbursts.
“It was theoretically considered that the surface of a magnetar could be experiencing a starquake, an energy release similar to earthquakes on Earth,” Totani explains.
“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.”
Fast radio bursts are one of the fascinating mysteries of the cosmos. As the name suggests, they are sudden releases of insanely powerful radio waves… but they last just milliseconds in length. In that time, they discharge as much energy as 500 million Suns. Most of them flare just once, making them unpredictable and difficult to study.
In recent years we’ve had some significant breakthroughs. A handful of fast radio burst sources repeat, allowing astronomers to watch them and analyze the signals they spit out. And, in 2020, for the first time, a fast radio burst was found coming from inside the Milky Way – which meant that astronomers could trace it to the very star that emitted it.
That star was a magnetar, a type of neutron star – the collapsed core that remains after a massive star has gone supernova. Magnetars have much more powerful magnetic fields than normal neutron stars though; in fact, they’re the most powerful known magnetic objects in the Universe.
This offers an explanation for these colossal eruptions. The magnetic field is so powerful that it distorts the magnetar’s shape, exerting an outward pull. Meanwhile, the density of the collapsed stellar core results in a powerful inward gravitational pull.
The tension between these two opposite forces causes the magnetar to rupture and quake, releasing powerful flares and perhaps, large amounts of electromagnetic energy in the form of radio waves – fast radio bursts.
Totani and Tsuzuki thought that a statistical analysis of the pattern of repeating fast radio sources might yield some clues – but not like such analyses have been previously performed.
Rather than concentrating just on the wait time between bursts, the two astronomers focused their attention on the time and emission energy of nearly 7,000 bursts from three sources.
Then, they applied the same time-energy correlation analysis to earthquake data here on Earth. And they also used it to analyze solar flares, another mechanism proposed to explain fast radio bursts.
“The results show notable similarities between FRBs and earthquakes,” Totani says.
“First, the probability of an aftershock occurring for a single event is 10-50 percent; second, the aftershock occurrence rate decreases with time, as a power of 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.”
Meanwhile, there was no notable similarity with solar flares. This suggests that, for those three fast radio burst sources at least, the starquake model is plausible.
There could be other explanations for other sources, so the bursts still retain some mystery; but the findings mean that these particular bursts could be studied to understand starquakes in general, and magnetars and neutron stars in particular.
“By studying starquakes on distant ultradense stars, which are completely different environments from Earth, we may gain new insights into earthquakes,” Totani says.
“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.”
The research has been published in the Monthly Notices of the Royal Astronomical Society.
