(ORDO NEWS) — The second time astronomers discovered a fast radio signal (FRB), which repeats in a regular cycle. This may mean that – in some cases – the unpredictability of mysterious signals from deep space may actually be a problem with our detection capabilities.
FRB 121102 is already known for being the most active of the detected radio signals since its discovery in 2012. It was believed that there was no reason for this – but a new analysis of the bursts revealed a pattern.
According to a thorough study of new and previously published observations, FRB 121102 exhibits repeated bursts over a period of 90 days, and then lulls for 67 days. Then this entire 157-day cycle is repeated again. If this analysis is correct, the source should have entered a new activity cycle on June 2 of this month.
This is an amazing discovery that can help find the possible causes of these mysterious signals. But at the same time, this is a demonstration of how strange and difficult to analyze these signals are.
“This is an amazing result because it is just the second system in which we see repeatability in explosive activity,” explained astronomer Kaustubh Rajwad of the University of Manchester.
“The detection of periodicity provides an important limitation on the origin of the bursts, and activity cycles may contradict the precession of neutron stars.”
Fast radio signals, one of the most exciting things that space throws at us, are extremely energetic bursts of radiation in the radio frequency spectrum, lasting only a few milliseconds. During this time, they can radiate as much energy as hundreds of millions of Suns.
Most of them flash only once, by chance, and astronomers never detect them again. This makes signals impossible to predict, although scientists are improving their skills in tracking these one-time bursts from sources.
Fewer sources show re-activity. This activity was also considered random – until this year, when it was discovered that a source called FRB 180916 was repeated cyclically. For four days, it could explode once or twice per hour, and then subside for 12 days. In general, its cycle is 16.35 days.
This, as you can see, is almost 10 times shorter than the FRB 121102 cycle. But if we assume that these two sources are similar and that the periodicity is caused by orbital motion, this range can be compared with known objects and find what causes them.
“If we now believe that orbital motion is the cause of the observed periodicity in FRB 121102, a large range of observed periods (16–160 days) can limit the possible binary systems,” the researchers write in their article.
So far, possible explanations for these powerful signals have included neutron stars, black holes, pulsars with companion stars, exploding pulsars, a hypothetical type of star called blitz, a connection with gamma-ray bursts (which, as we now know, can be caused by colliding neutron stars ), magnetars emitting gigantic flashes, and alien civilizations (unlikely).
The discovery at the end of April of a magnetar inside the Milky Way galaxy, spewing an extremely powerful radio signal, convincingly indicates that magnetars are the source of some fast radio bursts.
It is also possible that we cannot detect all the activity from each source — that they all repeat, but with different strengths, with weaker signals below our detection threshold.
“This exciting discovery highlights how little we know about the origin of fast radio signals,” said physicist and astronomer Duncan Lorimer of the University of West Virginia. “Further observations of a large number of likely sources are needed in order to get a clearer picture and find out their origin.”
The study is published in the Royal Astronomical Society Monthly Notices.
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