Intermediate-Mass Black Holes

Jenny E. Greene, Jay Strader, Luis C. Ho

Research output: Contribution to journalReview articlepeer-review

316 Scopus citations


We describe ongoing searches for intermediate-mass black holes with MBH≈ 10-105M⊙. 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 109-1010M⊙ galaxies hosting black holes with MBH∼ 105M⊙. 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 MBH≈ 100-104M⊙. ▪Considering low-mass galaxies with dynamical black hole masses and constraining limits, we find that the MBHrelation continues unbroken to MBH∼105M⊙, 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.

Original languageEnglish (US)
Pages (from-to)257-312
Number of pages56
JournalAnnual Review of Astronomy and Astrophysics
StatePublished - 2020

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • active galactic nuclei
  • globular clusters
  • gravitational waves
  • tidal disruption
  • ultraluminous X-ray sources


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