How is a black hole formed
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Formation of Black Holes: Mechanisms and Processes
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 is the collapse of large amplitude perturbations in the early Universe. These perturbations, characterized by a specific threshold amplitude, collapse under their own gravity when they reenter the cosmological horizon during the radiative era . The shape of the initial energy density profile plays a crucial role in determining the threshold for PBH formation .
Stellar Black Holes Formation
Direct Collapse of Massive Stars
Stellar black holes can form directly from the collapse of massive stars without a supernova explosion. For instance, the black hole in the x-ray binary Cygnus X-1 formed in situ from a progenitor star with an initial mass greater than 40 solar masses. This process involves minimal mass ejection, suggesting that high-mass stellar black holes may form promptly when massive stars collapse silently .
Implosion and Delayed Formation
Another pathway involves a proto-neutron star undergoing a supernova explosion with insufficient energy to unbind the stellar envelope. The remaining material falls back onto the neutron star, leading to the delayed formation of a black hole. Observational evidence supports this mechanism, showing that some black holes form without significant matter ejection or natal kicks .
Supermassive Black Holes Formation
Direct Collapse in Protogalactic Halos
Supermassive black holes (SMBHs) can form directly in the nuclei of protogalaxies through the rapid loss of angular momentum in self-gravitating gas within dark matter halos. This process, known as the "bars within bars" mechanism, leads to the formation of a dense core that collapses under its own gravity, forming a black hole. The initial mass of these black holes can be around 20 solar masses, with potential growth to quasar-size masses through super-Eddington accretion .
Turbulent Accretion and Mergers
In the early Universe, SMBHs can also form through the direct collapse of gas in atomic cooling halos with high virial temperatures. Turbulence regulates accretion and angular momentum transport, allowing the central object to grow rapidly. Simulations show that these black holes can reach masses of up to 10^6 solar masses within a million years through accretion and mergers .
Conclusion
Black holes can form through various mechanisms, including the collapse of cosmological perturbations, direct collapse of massive stars, and the rapid accretion of gas in protogalactic halos. Each pathway involves unique physical processes and conditions, contributing to the diverse population of black holes observed in the Universe.
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