Routing protocol

Globular cluster

Physics

Astronomy

Supermassive black hole

Intermediate-mass black hole

Gravitational wave

Accretion (finance)

Computer network

Binary black hole

Redshift

Computer science

Astrophysics

Black hole (networking)

Routing (electronic design automation)

Link-state routing protocol

Galaxy

Annual Review of Astronomy and Astrophysics

We describe ongoing searches for intermediate-mass black holes with M BH ≈ 10–10 5 M ⊙ . We review a range of search mechanisms, both dynamical and those that rely on accretion signatures. We find the following conclusions: ▪ Dynamical and accretion signatures alike point to a high fraction of 10 9 –10 10 M ⊙ galaxies hosting black holes with M BH ∼ 10 5 M ⊙ . In contrast, there are no solid detections of black holes in globular clusters. ▪ There are few observational constraints on black holes in any environment with M BH ≈ 100–10 4 M ⊙ . ▪ Considering low-mass galaxies with dynamical black hole masses and constraining limits, we find that the M BH –σ * relation continues unbroken to M BH ∼10 5 M ⊙ , albeit with large scatter. We believe the scatter is at least partially driven by a broad range in black hole masses, because the occupation fraction appears to be relatively high in these galaxies. ▪ We fold the observed scaling relations with our empirical limits on occupation fraction and the galaxy mass function to put observational bounds on the black hole mass function in galaxy nuclei. ▪ We are pessimistic that local demographic observations of galaxy nuclei alone could constrain seeding mechanisms, although either high-redshift luminosity functions or robust measurements of off-nuclear black holes could begin to discriminate models.

Intermediate-Mass Black Holes