How do black holes form
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How Do Black Holes Form?
Black holes are one of the most fascinating and enigmatic objects in the universe. Their formation can occur through several mechanisms, each contributing to the diverse population of black holes observed today. This article explores the primary pathways through which black holes form, including primordial black holes, stellar collapse, and the formation of supermassive black holes.
Primordial Black Holes Formation
Electroweak Phase Transition
Primordial black holes (PBHs) can form during the early universe through mechanisms such as 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 called Fermi-balls. These solitons collapse into PBHs due to internal Yukawa forces, potentially contributing to dark matter .
Inflaton Fragmentation
Another mechanism for PBH formation is the fragmentation of the inflaton field into long-lived spatially localized configurations known as oscillons. These oscillons can collapse into black holes, producing PBHs of sublunar mass, which could account for all dark matter. This process is particularly relevant for gravitational wave astronomy .
Numerical Relativity Simulations
Numerical relativity simulations have shown that PBHs can form from subhorizon and superhorizon perturbations in a matter-dominated universe. The formation can occur via direct collapse of the initial overdensity or through post-collapse accretion of ambient dark matter. This process results in rapid mass growth of the PBH beyond the self-similar limit .
Stellar Collapse
High-Mass Stellar Collapse
Black holes can also form from the collapse of massive stars. For instance, the black hole in the x-ray binary Cygnus X-1 was formed in situ without a supernova trigger. The progenitor star had an initial mass greater than 40 solar masses, and the collapse resulted in a black hole of approximately 10 solar masses. This suggests that high-mass stellar black holes may form promptly when massive stars disappear silently .
Supermassive Black Holes Formation
Direct Collapse in Protogalactic Halos
Supermassive black holes (SMBHs) can form directly in the nuclei of protogalaxies without the need for seed black holes from early star formation. In this scenario, self-gravitating gas in dark matter halos loses angular momentum rapidly through global dynamical instabilities, leading to the formation of a dense core. This core undergoes catastrophic cooling by thermal neutrino emission, resulting in the formation and rapid growth of a central black hole .
Gravothermal Collapse of Dark Matter Halos
Another pathway for SMBH formation involves the gravothermal collapse of self-interacting dark matter (SIDM) halos. This process leads to the formation of very massive SMBHs directly from SIDM halos, without the need for baryons or prior star formation. Smaller halos can produce seed black holes that merge and accrete to reach the SMBH range .
High-Resolution Simulations
High-resolution cosmological simulations have shown that direct collapse in atomic cooling halos with virial temperatures above 10,000 K can lead to the formation of massive seed black holes. Turbulence plays a crucial role in regulating accretion and transporting angular momentum, allowing the central object to grow significantly within a short period .
Conclusion
Black holes can form through various mechanisms, each contributing to the diverse black hole population observed in the universe. Primordial black holes can arise from early universe processes like electroweak phase transitions and inflaton fragmentation. Stellar black holes form from the collapse of massive stars, while supermassive black holes can emerge from direct collapse in protogalactic halos or gravothermal collapse of dark matter halos. Understanding these formation pathways provides valuable insights into the evolution and distribution of black holes across cosmic time.
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Most relevant research papers on this topic
Primordial black holes from an electroweak phase transition
Primordial black holes can form through a first-order electroweak phase transition, with potential dark matter candidates and experimental signals including gravitational waves and multi-lepton/jet final states.
Formation of supermassive black holes by direct collapse in pre-galactic haloes
Supermassive black holes can form directly in protogalaxies through rapid collapse in pre-galactic haloes, potentially providing the seeds for all present-day black holes.
A Brief Review on Primordial Black Holes as Dark Matter
Primordial black holes are a potential candidate for dark matter, with their formation, abundance, and signatures potentially impacting the evolution of the Universe and the formation of structures.
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