How is a supermassive black hole formed
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Formation of Supermassive Black Holes
Supermassive black holes (SMBHs) are colossal entities, often found at the centers of galaxies, with masses ranging from millions to billions of times that of the Sun. Understanding their formation, especially in the early universe, remains a significant challenge in astrophysics. Various theories and models have been proposed to explain their rapid emergence and growth.
Direct Collapse Model
One of the most plausible scenarios for the formation of SMBHs is the direct collapse of massive gas clouds in the early universe. This model suggests that self-gravitating gas in dark matter haloes can lose angular momentum rapidly through global dynamical instabilities, leading to the formation of a dense core. This core, supported by gas pressure and surrounded by a radiation pressure-dominated envelope, contracts and eventually forms a black hole through catastrophic cooling by thermal neutrino emission Latif2013Begelman2006. Simulations have shown that such conditions can lead to the formation of black holes with initial masses around 20 solar masses, which can grow rapidly to reach masses between 10^4 and 10^6 solar masses .
Seed Black Holes from Massive Stars
Another pathway involves the formation of seed black holes from the core-collapse of massive stars or the dynamical evolution of dense nuclear star clusters. These seed black holes, formed early in the universe, can grow through rapid accretion or mergers with other black holes and galaxies . Supermassive stars, with masses around 10^6 solar masses, are also considered potential progenitors of SMBHs. These stars can form in environments where matter accumulates at rates exceeding 1 solar mass per year, leading to the formation of black holes with masses in the range of 10^4 to 10^5 solar masses .
Role of Turbulence and Accretion
Turbulence plays a crucial role in the formation and growth of SMBHs by regulating accretion and transporting angular momentum. High-resolution cosmological simulations have shown that turbulence can lead to the formation of massive seed black holes in atomic cooling haloes with virial temperatures above 10^4 K. These simulations indicate that while fragmentation can occur, it does not prevent the growth of a central massive object through turbulent accretion and occasional mergers .
Galaxy Mergers and SMBH Binaries
Galaxy mergers are another significant factor in the formation of SMBHs. When two massive galaxies merge, their central black holes can form a binary system. Hydrodynamical simulations have demonstrated that such mergers can lead to the formation of a massive, turbulent nuclear gaseous disk, which facilitates the rapid formation of an eccentric SMBH binary. This process can occur within a million years, driven by gravitational drag from the gas .
Influence of Supersonic Gas Streams
Supersonic gas streams, resulting from velocity offsets between gas and dark matter components, can also enhance the formation of massive black holes. These streams prevent early gas cloud formation until rapid gas condensation is triggered in a protogalactic halo. This leads to the formation of a protostar, which grows through sporadic mass accretion and eventually collapses into a black hole with tens of thousands of solar masses, providing a promising seed for SMBHs .
Conclusion
The formation of supermassive black holes is a complex process influenced by various factors, including direct collapse of gas clouds, seed black holes from massive stars, turbulence, galaxy mergers, and supersonic gas streams. Each of these mechanisms contributes to our understanding of how these colossal entities emerged and grew rapidly in the early universe. Further research and advanced simulations continue to shed light on this fascinating aspect of cosmic evolution.
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