Radio waves

Pattern in radio waves: first contact, right?

Periodic radio waves hitting Earth from a nearby galaxy are unlikely to come from extraterrestrials, but the possibility cannot be ruled out.

The CHIME radio telescope in Canada has been recording Fast Radio Burst (FRB) 180916.J0158+65 since 2018. (Inset) Image of the host galaxy with the region containing the FRB source outlined in green (Photographs: Dunlap Institute/CHIME Collaboration, AURA )

All possibilities must be considered, including an artificial origin, says Abraham Loeb, director of the astronomy department at Harvard University, USA, referring to periodic bursts of radio waves emanating from a galaxy located 500 million light-years from Earth.

First noticed in September 2018 by the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope at the Dominion Radio Astrophysical Observatory in British Columbia, Canada, the waves created ripples around the world for a reason: they come in a pattern. This has given rise to theories that they may have originated from an extraterrestrial civilization.

Fast radio bursts (FRBs) are not a new concept. The first was noticed in 2007 and scientists have documented 110 FRBs so far. A large majority of FRBs are isolated, with only 10 so far repeating. Even rarer is the identification of the host galaxy of the source of the FRBs, which occurred with only four FRBs.

But none have been as remarkable as the current signal. In addition to repeating and helping to identify its host galaxy and source (named FRB 180916.J0158+65 by CHIME scientists), it arrived in 16-day cycles, accurate to the nearest second. The wave hits the Earth for a millisecond once or twice an hour for four days, then falls silent for 12 days. Between September 2018 and October 2019, CHIME documented 28 such cycles.

Shriharsh Tendulkar, a postdoctoral fellow in the Department of Physics at McGill University, Canada, and one of the researchers studying FRB 180916.J0158+65 said Down to earth on February 20, 2020, that the signal was still received. He, however, did not reveal whether the pattern also remained, saying the data could not be released since the study was ongoing. Nevertheless, what causes FRBs to repeat remains a mystery that scientists continue to wrestle with.

Initially, it was believed that the collision of black holes or neutron stars (extremely dense and small stars, with a radius sometimes as short as 50 km, composed mainly of neutrons) triggered them. But the discovery of repeating FRBs debunked the theory of colliding objects.

“FRBs are very likely to be the bright analogues of pulsars, which are rotating neutron stars with strong magnetic fields,” Loeb speculates. Another possible source of FRBs could be very young neutron stars (only decades old) with extremely strong magnetic fields, called magnetars, he says. Another possibility is that FRBs are a mixed population, with a variety of source types, he says.

The reason behind the periodicity could also be different. The cyclicity of FRB 180916.J0158+65 suggests something in the source’s orbit is causing the explosions, says Seth Shostak, an astronomer with Search for Extraterrestrial Intelligence (SETI), a nonprofit research institute. profit based in Mountain View, California, USA. “Perhaps an exotic star surrounding a black hole, or the other way around,” adds Shostak.

Loeb says that the periodicity could be due to the origin of the FRB of a binary star system (two stars revolving around each other), the revolution of one blocking the radio wave of the other towards Earth. It could also be caused by the orientation of the radio beam changing due to unknown factors, he says. So how can FRBs be studied?

If we discover an extremely bright and repeating FRB in a nearby source, we could study its surroundings in detail and identify its nature, Loeb says. “Another breakthrough could come from detecting FRBs at other wavelengths besides radio (optical, infrared or X-ray). This could provide an important clue to the nature of their central engine,” says Loeb. To illustrate, if the wave is in the optical spectrum, we will be able to see the source of the FRB.

Extraterrestrial sources

“Could it be that the radio bursts are caused by extraterrestrials trying to either make contact or just make their presence known? Don’t bet on it,” Shostak says. FRBs are an extremely inefficient means of communication because it’s impossible to fit a lot of information into a short radio burst, he says. A civilization trying to make contact is likely to opt for a more informative mode of communication.

Shostak also says that the FRBs whose locations we have identified are all over the universe, separated by billions of light years. “This means that any extraterrestrial memo asking others to make the same type of short transmissions to the cosmos would arrive billions of years apart. A coordinated response seems unlikely,” he says.

Loeb disagrees with Shostak and says the signal might not be coordinated or intentional, but that doesn’t rule out the possibility that its source was an extraterrestrial civilization. The issue is not “cooperation, because strong signals are not necessarily used for communication. A civilization could generate a powerful beam of light to propel cargo and we would detect the leak of that radiation,” he explains.

Despite differing views, scientists say the discovery is huge. Just as the discovery of the multilingual Rosetta Stone in 1799 helped decode Egyptian hieroglyphs, this new member of the cosmic bestiary may unlock an understanding of what FRBs really are,” says Shostak.

In the meantime, no option can be ruled out.