Say you're an alien civilization with advanced technology looking to communicate with other civilizations throughout the Milky Way galaxy. Where would you be setting up your beacon? Probably close to home, right?
The galactic center – that crowded, fascinating region around supermassive black hole Sagittarius A* – is one of the best spots in the Milky Way for sending sweeping, repeating radio signals out to whoever might be listening.
That's according to a team of scientists led by astronomer Akshay Suresh of Cornell University, who have devised a way to look for these signals.
The Breakthrough Listen Investigation for Periodic Spectral Signals (BLIPSS) project is designed to seek and amplify strangely pulsed radio emission from the galactic center that may be messages from extraterrestrial intelligences.
"BLIPSS showcases the cutting-edge potential of software as a science multiplier for SETI," Suresh explains.
The galactic center is a very hectic place, filled with all sorts of stars, and thick clouds of dust and gas that obscure much of whatever is in there. In addition, there are natural objects that do send out repeating radio signals.
However, it's also very cluttered, compared to other regions of the sky; statistically, given the large number of stars in the galactic center line-of-sight, it offers the greatest potential for being the direction in which a habitable exoplanet lies.
If we're going to find an alien signal, that's one of the best places to look, but it's not without its challenges. Teasing out an artificial signal from the natural cacophony of light emanating from the galactic center is quite a monumental task.
Periodic pulsed beacons would be an inexpensive way of transmitting signals across vast tracts of interstellar space. Here on Earth, we use pulsed signals for applications such as remote radar sensing and aircraft navigation, but scaled up by sufficiently advanced technology, they could be sent much farther.
BLIPSS uses what is known as a fast folding algorithm, which is a highly sensitive search technique for identifying periodic signals. In the past, for example, scientists have used it to search for a type of star called a pulsar, which emits periodic pulses of light.
Suresh and his colleagues set the fast folding algorithm to a different task. They deployed BLIPSS on radio surveys of data of the galactic center collected as part of the SETI Institute's Breakthrough Listen initiative, which took 7-hour and 11.2-hour observations of the galactic center using the Murriyang radio telescope in Parkes in Australia, and the Green Bank Telescope, respectively.
BLIPSS was run on 4.5 hours' worth of Green Bank Telescope data between the ranges of 4 and 8 gigahertz.
The researchers tested their software on pulsars to make sure it was capable of detecting the sorts of signals they were looking for, and narrowed the frequency range, refining it to less than a tenth of the range occupied by an FM radio station, with pulse periodicities between 11 and 100 seconds.
They found no signals that matched their search parameters, but the effort demonstrated the effectiveness of their techniques, and the team feels confident using it across different search parameters in the future.
"Until now, radio SETI has primarily dedicated its efforts to the search for continuous signals," says astronomer Vishal Gajjar of the SETI Institute.
"Our study sheds light on the remarkable energy efficiency of a train of pulses as a means of interstellar communication across vast distances. Notably, this study marks the first-ever comprehensive endeavor to conduct in-depth searches for these signals."
A paper describing the results has been published in The Astronomical Journal.