SMBH

SMBH stands for supermassive black hole, a class of black holes with masses ranging from about one million to several billion solar masses. They are believed to reside at the centers of most massive galaxies, including the Milky Way. Observational evidence comes from stellar and gas dynamics showing a compact, very massive object in galactic nuclei, as well as luminous active galactic nuclei when material accretes onto the black hole, producing strong electromagnetic emission across the spectrum and, in some cases, relativistic jets.

Mass measurements are obtained by tracking orbits of stars near the center (stellar dynamics), motion of gas and maser emission, and, for active nuclei, reverberation mapping and broad emission line properties. The M-sigma relation links black hole mass to the velocity dispersion of the host galaxy's bulge, suggesting coevolution.

Formation and growth occur via accretion of gas and mergers with other black holes. Seed black holes may form in early galaxies and grow rapidly in gas-rich environments, giving rise to quasars in the early universe.

Prominent examples include Sagittarius A*, the ~4 million solar mass SMBH at the center of the Milky Way; and M87*, the several-billion-solar-mass SMBH in the elliptical galaxy M87, imaged by the Event Horizon Telescope. SMBHs power active galactic nuclei and, in some cases, relativistic jets.

During active phases, accretion disks radiate efficiently, with luminosity capped by the Eddington limit. Through feedback processes, such as winds and jets, SMBHs influence star formation and the evolution of their host galaxies.