[CSL] Gravitational Waves (A)

Description: Gravitational-wave astronomy has rapidly evolved into a leading and multi-disciplinary research field. UK-based science heavily contributes to this effort, with participation in the LIGO Scientific and Einstein Telescope Collaborations and the LISA, Pulsar Timing Array and Cosmic Explorer Consortia. Using the instruments pioneered by these groups, we expect to observe gravitational-waves extending from nanohertz to kilohertz frequencies.

The hertz to kilohertz end of the gravitational-wave spectrum is already being unveiled by the LIGO and Virgo detectors: close to 100 gravitational-wave candidates have been discovered. Although these signals span a discrete portion of the full gravitational-wave spectrum, they reveal much about binaries containing black holes and neutron stars: for example, they show structure in the black hole mass distribution, demonstrate that black holes have small spins, and confirm the connection between neutron-star collisions and kilonovae. The origin(s) of these binaries is an open question; various environments including the galactic field, star clusters and active galactic nuclei, have been proposed as possible explanations. Ground-based interferometers can also probe the origins of galaxies with studies investigating the properties of active galactic nuclei and searches for dark matter. The instruments continue to undergo upgrades to reduce the impact of noise, meaning that the fourth gravitational-wave observing run should yield daily detections and the potential for discovery of new source types. A growing catalogue will yield independent and precise constraints on the neutron star equation of state, the Hubble constant and the star formation rate.

The millihertz region of the gravitational-wave spectrum will be analysed by future space-borne detectors including LISA, allowing the detection of thousands of gravitational-wave sources: massive black-hole mergers, extreme mass-ratio inspirals, millions of galactic binaries, and more. These detections will enhance our understanding of stellar and early galaxy evolution, the growth and merger history of massive black holes, and probe the rate of expansion of the Universe. LISA will undergo adoption review by ESA this year and is due to launch in the early 2030s. Still, many challenges in instrumentation and data analysis must be solved before LISA flies. LISA Data Challenges function as a call to test algorithms that will answer numerous questions on black-hole astrophysics, galaxy formation, cosmology, and tests of general relativity. 

Pulsar timing arrays seek to detect nanohertz gravitational-wave signals created by the most massive black holes in the Universe. The pulsar timing array consortia have seen speculative hints of a first detection, and further results are expected this year: the ever-expanding pulsar population and longer observation spans give rise to increasingly sensitive data. There is much to be discovered, including insights into the formation and evolution of massive black hole binaries and their host galaxies. New facilities such as the SKA are expected to be transformative.

These sessions address all areas of astronomy and astrophysics that are affected by gravitational-wave observations, as well as the potential of multi-messenger work. This includes electromagnetic counterparts, cosmic rays, supernovae, extragalactic neutrinos, and more. Anyone whose research is related to gravitational-wave science is encouraged to submit an abstract.