what types of black holes are there

Gravitational Singularities and Event Horizons: A Classification

Celestial objects characterized by immense gravitational fields that prevent anything, including light, from escaping. Their classification is based primarily on mass and formation mechanisms.

Stellar-Mass Objects

Formed from the gravitational collapse of massive stars at the end of their life cycle. When a star exhausts its nuclear fuel, it can no longer support itself against its own gravity, leading to a supernova explosion and, under certain conditions, the formation of a dense, compact object.

  • Mass Range: Typically range from a few to several tens of solar masses (M☉).
  • Formation Mechanism: Core-collapse supernova. The core collapses under its own gravity, exceeding the Tolman-Oppenheimer-Volkoff limit.
  • Detection Methods: Often detected through X-ray binaries (where they accrete matter from a companion star) and gravitational waves from mergers.

Intermediate-Mass Objects (IMBHs)

A hypothesized class of objects with masses between stellar-mass and supermassive objects. Their existence is still debated and subject to ongoing research.

  • Mass Range: Roughly 102 to 105 M☉.
  • Formation Hypotheses: May form through runaway collisions of massive stars in dense star clusters, or from the direct collapse of massive gas clouds.
  • Detection Challenges: Difficult to detect due to their relatively small size and lack of strong accretion disks compared to supermassive objects. Searches focus on tidal disruption events and gravitational wave signatures.

Supermassive Objects (SMBHs)

Located at the centers of most galaxies, including our own Milky Way. They play a crucial role in galaxy formation and evolution.

  • Mass Range: Millions to billions of solar masses (M☉).
  • Formation Mechanisms: The exact formation mechanism is not fully understood, but several theories exist, including:
    • Direct Collapse: The direct collapse of massive gas clouds without forming a star.
    • Hierarchical Merging: Mergers of smaller black holes and accretion of surrounding gas and stars.
    • Stellar Black Hole Growth: Gradual growth of stellar objects through accretion over cosmic timescales.
  • Detection Methods: Detected through their gravitational influence on surrounding stars and gas, and by the radiation emitted from accretion disks (active galactic nuclei, or AGN). Event Horizon Telescope observations have directly imaged the shadow of SMBHs.

Primordial Objects

Hypothetical objects that may have formed in the very early universe due to density fluctuations during the inflationary epoch. Their existence is purely theoretical.

  • Mass Range: Could theoretically have a wide range of masses, from very small (Planck mass) to very large.
  • Formation Mechanism: Formed from density fluctuations in the early universe. These fluctuations could have collapsed under their own gravity to form primordial objects.
  • Detection Challenges: Extremely difficult to detect. Searches focus on gravitational lensing effects, gravitational waves, and their possible contribution to dark matter. Their existence remains unconfirmed.