Every year, hundreds of thousands of black hole pairs converge in a cosmic dance that emits gravitational waves in all directions. Since 2015, the large ground-based interferometers LIGO, Virgo and KAGRA have made it possible to detect these signals, but only about a hundred such events have been observed, an infinitesimal fraction of the total. Most of the waves remain “indistinguishable”, overlapping and collecting, creating a flat, diffuse background signal that scientists call the “stochastic gravitational wave background” (SGWB).

A new SISSA study published in Astrophysical Journalsuggests using three or four arrays of space-based interferometers to map a flat and almost perfectly uniform background to look for waves. Known to scientists as anisotropy, these tiny fluctuations contain information necessary to understand the distribution of gravitational wave sources on the widest cosmological scale.

Researchers believe that next-generation detectors such as the Einstein Telescope and Laser Interferometer Space Antenna (LISA) will enable direct measurements of the gravitational wave background in the near future.

“Measuring these background fluctuations, better known as anisotropies, but identifying them will be extremely difficult, as they require very high levels of angular resolution that current and next-generation geodetic devices don’t have,” explains Julia Kapurri, PhD, of SISSA. D. is a student and first author of the study.

Capurri suggested, under the supervision of Carlo Baccigalupi and Andrea Lapi, that this problem could be overcome with a “constellation” of three or four solar-orbiting space interferometers spanning a distance close to that between the Earth and the Sun. As the distance increases, interferometers achieve better angular resolution, improving their ability to distinguish gravitational wave sources.

“A constellation of space interferometers orbiting the Sun can enable us to see subtle fluctuations in the gravitational background signal, thereby gaining valuable information about the distribution of black holes, neutron stars, and all the other gravitational waves in the universe,” Kapurri says.

After the successful testing of the LISA project’s space mission, there are currently two proposals for the creation of space-based interferometer arrays: a European – Big Bang Observatory (BBO) and a Japanese – Gravitational Wave Observatory of Decighertz Interferometer. (DECIGO).

“This is one of the earliest studies to provide specific estimates of the size of the stochastic gravitational wave background using a constellation of instruments orbiting the Sun. Along with other similar projects, details of which will be published over time, it is the most optimal for future observing instruments that we hope will be built and operational in the coming decades.” They will be crucial to the development of suitable designs.” Professor of theoretical cosmology at SISSA.

In the era of multi-messenger astronomy that began with ground-based interferometers like LIGO and Virgo, the gravitational wave background could pave the way for a new understanding of the universe at large scales, just as the cosmic microwave background has already done. .