Powerful, rapid-fire radio waves emanating from deep space confound scientists
Scientists have gathered more data on a series of mysterious, intermittent radio waves emanating from a distant object in space but are still only able to theorise what causes them.
The radio waves are so bright that they’re supposedly visible across much of the nearby universe and are nearly 100 per cent linearly polarised, an indication that the source of the bursts is embedded in strong magnetic fields like those around a massive black hole.
Scientists at UC Berkley’s Breakthrough Listen project have been speculating about the nature of the source of the waves, which has been called FRB 121102.
The project began last year and is tasked with searching for intelligent, extra-terrestrial communications in the Universe. It has already raked in $100m in funding and used thousands of hours of dedicated telescope time on state-of-the-art facilities.
More than 200 high-energy bursts have been observed coming from the source, which is located in a dwarf galaxy about 3 billion light years from Earth.
The near-100-per-cent polarisation 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 centres of galaxies.
The team has suggested that the fast radio bursts (FRBs) may come from a highly magnetised 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 kilometres 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 magnetised wind from a rotating neutron star, or a pulsar.
“At this point, we don’t really know the mechanism. There are many questions, such as, how can a rotating neutron star produce the high amount of energy typical of an FRB?” 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 SETI and other types of astronomy,” said Andrew Siemion, director of the Berkeley SETI Research Center and of the Breakthrough Listen programme. “We look forward to working with the international scientific community to learn more about these enigmatic and dynamic sources.”
Another possibility, though remote, is that the FRB is a high-powered signal from an advanced civilisation. “We cannot 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.
Breakthrough Listen allotted tens of hours of observational time on the Green Bank Telescope to recording radio emissions from FRB 121102, and on 26 August 2017 detected 15 bursts over a relatively short period of five hours.
The team plans a few more observations of FRB 121102 before moving on to other FRB sources. Gajjar said that they want to observe at higher frequencies - up to 12GHz, versus the present Green Bank observations in the 4-8GHz range - to see if the energy drops off at higher frequencies. This could help narrow the range of possible sources, he said.
A team of researchers recently debunked a theory that aliens could be responsible for the unusual dimming and brightening of a distant star, although they still don’t understand its odd behaviour.