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Space Interferometer Constellation To Reveal Elusive Gravitational Wave Sources and Unravel the Universe

LISA – Laser Interferometer Space Antenna. Credit: Simon Barke – University of Florida

A new SISSA study proposes an array of interferometers in space to detect subtle fluctuations in the background gravitational signals that may reveal the secrets of black holeA black hole is a place in space where the gravitational field is so strong that not even light can escape it. Astronomers classify black holes into three categories by size: miniature, stellar, and supermassive black holes. Miniature black holes could have a mass smaller than our Sun and supermassive black holes could have a mass equivalent to billions of our Sun.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>black hole mergers.

Researchers at SISSA have proposed using a constellation of three or four space interferometers to detect anisotropies in the stochastic gravitational wave background (SGWB), which could reveal valuable information about the distribution of black holes, neutron stars, and other gravitational wave sources in the universe. Current and next-generation detectors, like the Einstein Telescope and LISA, lack the high level of angular resolution needed to measure these anisotropies. However, a constellation of space interferometers orbiting the Sun could achieve better angular resolution, enhancing our understanding of the universe on a larger scale.

Every year, hundreds of thousands of pairs of black holes merge in a cosmic dance that emits gravitational waves in every direction. Since 2015, the large ground-based LIGOThe Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory supported by the National Science Foundation and operated by Caltech and MIT. It's designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. It's multi-kilometer-scale gravitational wave detectors use laser interferometry to measure the minute ripples in space-time caused by passing gravitational waves. It consists of two widely separated interferometers within the United States—one in Hanford, Washington and the other in Livingston, Louisiana.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>LIGO, Virgo and KAGRA interferometers have made it possible to detect these signals, although only about a hundred such events, an infinitesimal fraction of the total, have been observed. Most of the waves remain ‘indistinguishable’, superimposed and added together, creating a flat, diffuse background signal that scientists call the ‘stochastic gravitational wave background’ (SGWB).

New SISSA research, published in The Astrophysical JournalThe Astrophysical Journal (ApJ) is a peer-reviewed scientific journal that focuses on the publication of original research on all aspects of astronomy and astrophysics. It is one of the most prestigious journals in the field, and is published by the American Astronomical Society (AAS). The journal publishes articles on a wide range of topics, including the structure, dynamics, and evolution of the universe; the properties of stars, planets, and galaxies; and the nature of dark matter, dark energy, and the early universe.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Astrophysical Journal, proposes using a constellation of three or four space interferometers to map the flat and almost perfectly homogeneous background in a search for ripples. These small fluctuations, known to scientists as anisotropies, hold the information needed to understand the distribution of gravitational wave sources on the largest cosmological scale.

Researchers are convinced that next-generation detectors, such as the Einstein Telescope and the Laser Interferometer Space Antenna (LISA), will make direct measurement of the gravitational wave background possible in the foreseeable future. “Measuring these background fluctuations, known more correctly as anisotropies, will however continue to be extremely difficult, as identifying them requires a very high level of angular resolution not possessed by current and next-generation survey instruments,” explains Giulia Capurri, a SISSA PhD student and first author of the study.

Capurri, supervised by Carlo Baccigalupi and Andrea Lapi, has suggested that this problem could be overcome by means of a ‘constellation’ of three or four space interferometers in solar orbit and covering a distance approximating that between Earth and the Sun. With increasing separation, interferometers achieve better angular resolution, improving their ability to distinguish sources of gravitational wavesGravitational waves are distortions or ripples in the fabric of space and time. They were first detected in 2015 by the Advanced LIGO detectors and are produced by catastrophic events such as colliding black holes, supernovae, or merging neutron stars.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>gravitational waves. “A constellation of space interferometers orbiting the Sun could enable us to see subtle fluctuations in the gravitational background signal, thus allowing us to extract valuable information about the distribution of black holes, neutron stars, and all other sources of gravitational waves in the universe,” states Capurri.

Following the success of the LISA project’s space mission test, there are currently two proposals for the creation of space-based interferometer constellations: one European – the Big BangThe Big Bang is the leading cosmological model explaining how the universe as we know it began approximately 13.8 billion years ago.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Big Bang Observatory (BBO), and one Japanese – the Deci-hertz Interferometer Gravitational-wave Observatory (DECIGO). “This represents one of the earliest work to provide specific predictions of the size of the stochastic background of gravitational waves by a constellation of instruments orbiting the Sun. Together with further similar projects whose details will be published in due course, they will be crucial for developing an optimal design for future observational instruments that we hope will be built and commissioned in the coming decades” concludes Carlo Baccigalupi, professor of theoretical cosmology at SISSA.

In the era of multimessenger astronomy, which began with ground-based interferometers such as LIGO and Virgo, the gravitational-wave background could pave the way to a new understanding of the universe on the large scale, as has already happened with the cosmic microwave background.

Reference: “Searching for Anisotropic Stochastic Gravitational-wave Backgrounds with Constellations of Space-based Interferometers” by Giulia Capurri, Andrea Lapi, Lumen Boco and Carlo Baccigalupi, 27 January 2023, The Astrophysical Journal.
DOI: 10.3847/1538-4357/acaaa3

Source: SciTechDaily