Recent observations of a mysterious and distant object that emits intermittent bursts of radio waves so bright that they’re visible across the universe provide new data about the source but fail to clear up the mystery of what causes them.
The observations by the Breakthrough Listen team at UC Berkeley show that the fast radio bursts from this object, called FRB 121102, are nearly 100 percent linearly polarized, an indication that the source of the bursts is embedded in strong magnetic fields like those around a massive black hole.
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Fast radio bursts are brief, bright pulses of radio emission from distant but so far unknown sources and FRB 121102 is the only one known to repeat: more than 200 high-energy bursts have been observed coming from this source, which is located in a dwarf galaxy about 3 billion light-years from Earth.
The nearly 100 percent polarization of the radio bursts is unusual and has only been seen in radio emissions from the extreme magnetic environments around massive black holes, such as those at the centers of galaxies. The Dutch and Breakthrough Listen teams suggest that the fast radio bursts may come from a highly magnetized rotating neutron star – a magnetar – in the vicinity of a massive black hole that is still growing as gas and dust fall into it.
The short bursts, which range from 30 microseconds to 9 milliseconds in duration, indicate that the source could be as small as 10 kilometers across – the typical size of a neutron star.
Other possible sources are a magnetar interacting with the nebula of material shed when the original star exploded to produce the magnetar; or interactions with the highly magnetized wind from a rotating neutron star, or pulsar.
“At this point, we don’t really know the mechanism. There are many questions” said UC Berkeley postdoctoral fellow Vishal Gajjar of Breakthrough Listen and the Berkeley SETI Research Center.
“This result is an excellent demonstration of the capabilities of the Breakthrough Listen instrumentation and the synergies between and other types of astronomy,” said Andrew Siemion, director of the Berkeley SETI Research Center and of the Breakthrough Listen program. “We look forward to working with the international scientific community to learn more about these enigmatic and dynamic sources.”
Are FRBs signals from advanced civilizations?
Another possibility, though remote, is that the FRB is a high-powered signal from an advanced civilization. Hence the interest of Breakthrough Listen, which looks for signs of intelligent life in the universe, funded by $100 million over 10 years from internet investor Yuri Milner.
“We can not rule out completely the ET hypothesis for the FRBs in general,” Gajjar said.
Breakthrough Listen has to date recorded data from a dozen FRBs, including FRB 121102, and plans eventually to sample all 30-some known sources of fast radio bursts.
“We want a complete sample so that we can conduct our standard SETI analysis in search of modulation patterns or narrow-band signals – any kind of information-bearing signal emitted from their direction that we don’t expect from nature,” he said.
