A European LOFAR research on low-frequency extraterrestrial radio signals that have never been explored before has begun. The well-known SETI program for the search of extraterrestrial intelligence has traditionally focused on radio frequencies higher than one gigahertz, such as the frequency of the hydrogen line at 1.42 GHz.
SETI astronomers tend not to consider lower frequencies because the Earth’s atmosphere makes this type of observation noisy. However, the European Low-Frequency Array, or LOFAR for short, is specifically designed to conduct radio astronomy at these frequencies.
Collaboration between LOFAR and SETI
LOFAR is a series of radio antennas that span hundreds of kilometers across Europe. The central facility is in the Netherlands, but additional stations are located in France, Germany, Ireland, Latvia, Poland, Sweden, and the United Kingdom. The stations incorporate two types of antennas. Low-band antennas operate between 10 and 90 MHz, and high-band antennas listen to the universe between 100 and 250 MHz.
In conjunction with the Breakthrough Listen project of SETI, the LOFAR stations in Ireland and Sweden have been used together in the initial phase of the first low-frequency search for extraterrestrial signals. This research used high-band antennas to listen to radio signals at frequencies between 110 and 190 MHz.
The aim is to detect leaks from high-power transmitters, such as planetary radars or communications with spacecraft. To date, the research has involved 1,631,198 stellar systems identified by NASA‘s Transiting Exoplanet Survey Satellite (TESS) and the Gaia probe from the European Space Agency (ESA).
LOFAR array update
Using multiple sites in Ireland and Sweden, astronomers have been able to negate the effects of terrestrial radiofrequency interference and quickly dismiss any false positives. If an anomalous signal is detected only by one station and not the others, it would be considered local interference. Only a signal from space could be detected by all stations simultaneously.
No narrowband radio signals with a characteristic frequency drift caused by the orbital motion of an exoplanet hosting a transmitter emitting signals with a power of at least tens of millions of watts have been detected. However, the low-frequency search is only in its early stages, and improvements in the coming years will increase its sensitivity.
“LOFAR will soon undergo a series of gradual array upgrades throughout Europe, enabling even broader SETI at ranges of 15-240 MHz” said Owen Johnson, lead author of the publication (ref.), in a recent statement (ref.). Among these upgrades will be two new LOFAR stations in Bulgaria and Italy. Additionally, new computer software will be implemented, and artificial intelligence algorithms will accelerate the analysis of the results.
“We have billions of stellar systems to explore, and we will rely on some machine learning techniques to sift through the immense volume of data” Johnson said. “This, in itself, is interesting: it would be quite ironic if humanity were to discover alien life using artificial intelligence.”