Gravitational wave emission from binary supermassive black holes

TL;DR

This paper reviews the role of massive black hole binaries as the strongest gravitational wave sources, discussing their formation, evolution, and the potential for direct detection through space-based interferometry and pulsar timing arrays.

Contribution

It provides a comprehensive overview of MBHBs as GW sources, connecting binary properties with gravitational wave signals and outlining detection prospects.

Findings

MBHBs are key GW sources in the universe.

Direct detection will reveal their physical and astrophysical properties.

Future observations will reconstruct their cosmic history and dynamics.

Abstract

Massive black hole binaries (MBHBs) are unavoidable outcomes of the hierarchical structure formation process, and according to the theory of general relativity are expected to be the loudest gravitational wave (GW) sources in the Universe. In this article I provide a broad overview of MBHBs as GW sources. After reviewing the basics of GW emission from binary systems and of MBHB formation, evolution and dynamics, I describe in some details the connection between binary properties and the emitted gravitational waveform. Direct GW observations will provide an unprecedented wealth of information about the physical nature and the astrophysical properties of these extreme objects, allowing to reconstruct their cosmic history, dynamics and coupling with their dense stellar and gas environment. In this context I describe ongoing and future efforts to make a direct detection with space based interferometry and pulsar timing arrays, highlighting the invaluable scientific payouts of such enterprises.