In a series of articles published today in “The Astrophysical Journal Letters” and “Astronomy and Astrophysics” researchers from EPTA, InPTA, PPTA, CPTA and NANOGrav have announced the detection of a ultra-low-frequency gravitational wave background.
The signal was isolated in decades of data from arrays of radiotelescopes studying the universe in the nanohertz regime. They observe pulsars and analyse changes in their very regular periodic signal due to the subtle stretching and squeezing of space-time that happens when a gravitational wave passes.
Unlike the signals detected by LIGO and Virgo these have an extremely low frequency, and would require a detector much larger than our planet to be observed. By putting together the information coming from a great number of pulsars astronomers turned our sector of the Milky Way Galaxy into a huge gravitational-wave detector, called pulsar timing array. This type of detector can detect signals with frequencies in the order of the nanoheartz, while LIGO and Virgo’s range goes from 10 Hz to 10kHz, therefore studying completely different sources, such as supermassive black holes, found in the centres of merging galaxies.
“It is remarkable how less than a decade after the first detection of gravitational waves, research in this field continues to open new windows of observation of the most remote and mysterious phenomena in our Universe – stated Gianluca Gemme, Virgo spokesperson – It would be exciting to complement these results in the coming years with new data on the stochastic gravitational wave background in the frequency band accessible to LIGO, Virgo and KAGRA. We will continue looking for it in the next observing runs!”