How does a black hole form from a massive star
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Formation of Black Holes from Massive Stars
Collapse of Massive Stars into Black Holes
Stellar Evolution and Core Collapse
Black holes form from the remnants of massive stars that have exhausted their nuclear fuel. When a star with a mass greater than approximately 20 times that of the Sun reaches the end of its life, it undergoes a supernova explosion. The core of the star collapses under its own gravity, leading to the formation of a black hole if the remaining mass is sufficient .
Pair-Instability Supernovae
In some cases, very massive stars (with masses between 140 and 260 times that of the Sun) undergo pair-instability supernovae. This process involves the production of electron-positron pairs in the star's core, leading to a partial collapse and subsequent explosion. If the star's mass is within a certain range, the explosion can be so powerful that it leaves no remnant. However, if the mass is higher, the core can collapse directly into a black hole .
Direct Collapse Black Holes
Formation in Metal-Free Halos
In the early universe, direct-collapse black holes can form from the rapid collapse of pre-galactic gas clouds. These clouds, which are metal-free, can collapse under their own gravity if they are exposed to a sufficient level of Lyman-Werner radiation, which prevents the formation of molecular hydrogen and thus star formation. This process leads to the formation of supermassive stars, which eventually collapse into black holes 38.
Role of Lyman-Werner Radiation
Lyman-Werner radiation plays a crucial role in the formation of direct-collapse black holes by destroying molecular hydrogen, which is necessary for cooling the gas and forming stars. This radiation can come from nearby star-forming regions, creating an environment where the gas cloud can collapse directly into a black hole without fragmenting into stars .
Black Hole Formation in Star Clusters
Dynamical Interactions in Dense Clusters
In dense star clusters, black holes can form through dynamical interactions. Massive stars in these clusters can collide and merge, forming more massive stars that eventually collapse into black holes. These interactions can lead to the formation of intermediate-mass black holes, which are larger than those formed through isolated stellar evolution .
Repeated Mergers
Black holes formed in star clusters can undergo repeated mergers. When two black holes merge, they form a new, more massive black hole. This process can continue, especially in dense environments, leading to the formation of very massive black holes. These repeated mergers are influenced by the initial spin of the black holes and the dynamics of the cluster .
Conclusion
The formation of black holes from massive stars involves complex processes that depend on the initial mass of the star, the environment in which it evolves, and the interactions it undergoes. From the collapse of massive stellar cores to the direct collapse of pre-galactic gas clouds and the dynamical interactions in star clusters, these processes highlight the diverse pathways through which black holes can form in the universe.
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