How does a black hole form
Pro Research Analysisby 
Searched over 200M research papers
How Does a Black Hole Form?
Primordial Black Holes Formation
Electroweak Phase Transition and Fermi-Balls
Primordial black holes (PBHs) can form through a first-order electroweak phase transition (FOEWPT). This process involves extending the Standard Model with a real singlet scalar, leading to the formation of non-topological solitons known as Fermi-balls. These solitons trap fermions in the false vacuum during the FOEWPT and eventually collapse into PBHs due to internal Yukawa forces .
Cosmological Perturbations
Another mechanism for PBH formation involves the collapse of large amplitude perturbations in the early Universe. These perturbations, characterized by a significant energy density, collapse when they reenter the cosmological horizon. The threshold for this collapse depends on the shape and amplitude of the initial energy density profile, which can be understood through spherical symmetry and gradient expansion approximations .
Black Holes from Stellar Collapse
Condensation of Matter
Black holes can also form when a sufficient amount of matter condenses in a small region, causing gravitational collapse. This process is well-explained by general relativity, where the intense gravitational effects lead to the formation of a black hole .
Formation in Isolated Systems
In isolated systems, such as an insulated box in thermal equilibrium, black holes can form and evaporate in a statistically time-symmetric manner. This process is more likely to occur adiabatically rather than through instabilities like the Jeans instability .
Supermassive Black Holes in the Early Universe
Direct Collapse in Atomic Cooling Halos
Supermassive black holes (SMBHs) in the early Universe can form through direct collapse in atomic cooling halos with high virial temperatures. This process involves the rapid build-up of a dense core supported by gas pressure, which eventually collapses into a black hole due to thermal neutrino emission. This mechanism can produce initial black holes with masses ranging from 20 to 10^6 solar masses 56.
Gravothermal Collapse of Dark Matter Halos
Another pathway for SMBH formation is through the gravothermal collapse of self-interacting dark matter (SIDM) halos. This process leads to the formation of very massive black holes directly from SIDM halos, without the need for baryons or prior star formation. Smaller halos can produce seed black holes that grow through mergers and accretion .
Formation and Evolution of Black Holes
Nonsingular Black Holes
Black holes can also form and evolve in a nonsingular manner. These black holes transition from an initial vacuum region to a static region supported by finite density and pressures, and eventually evaporate back to a vacuum region. This dynamic process involves ingoing and outgoing radiation fluxes, maintaining a smooth trapping horizon .
Formation in X-ray Binaries
In some cases, black holes form in situ without an energetic trigger from a nearby supernova. For example, the black hole in the x-ray binary Cygnus X-1 formed directly from a progenitor star with an initial mass greater than 40 solar masses, collapsing silently into a black hole .
Conclusion
Black holes can form through various mechanisms, ranging from the collapse of cosmological perturbations and stellar matter to the direct collapse in dark matter halos and atomic cooling halos. These processes highlight the diverse pathways through which black holes, including primordial and supermassive ones, can emerge in the Universe.
Sources and full results
Most relevant research papers on this topic