Circumbinary disk accretion

Gaseous accretion disks are common throughout the Universe, forming around both single and multiple systems, including binary stars and black holes. Circumbinary disks, shaped by the gravitational influence of two central bodies, exhibit distinctive short- and long-term dynamics. These disks often feature a central cavity cleared by the binary's orbital motion, as well as asymmetries, spirals, or eccentric shapes. The complex gravitational interactions influence both the disk and binary evolution, with important implications for the formation and early evolution of stellar binaries, and the orbital dynamics and mergers of massive black hole binaries in galactic nuclei. The distinct morphology, variability, and radiation emitted by these disks can be used to infer the presence of binaries, even when the central objects remain unresolved. In particular, electromagnetic radiation from the disk can signal the presence of weakly relativistic binaries long before their coalescence. Understanding the intricacies of circumbinary accretion is essential for uncovering the formation of binary and multiple stellar systems and for advancing our knowledge of massive black hole evolution in the era of multi-messenger astronomy.