How hot are black holes
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How Hot Are Black Holes?
Black Hole Temperature and Formation
When a massive star collapses to form a black hole, a significant amount of heat is generated, leading to an increase in the black hole's internal temperature. This process involves nuclear interactions, such as the fusion of quarks, which further elevate the temperature. At a certain point, the thermal energy density of the black hole matches its mass-energy density, stabilizing its structure against further collapse. This concept aligns with Hawking's black hole temperature formula, suggesting that black holes are inherently hot rather than cold .
Hawking Radiation and Primordial Black Holes
Primordial black holes (PBHs) in the early universe emit Hawking radiation, which heats the surrounding plasma. This results in a hot spot around the PBH with a temperature profile that includes a core much larger than the black hole's horizon. The highest temperature of this hot spot is independent of the PBH's initial mass, reaching up to 2 × 10^9 GeV, influenced by fine-structure constants . Additionally, microscopic black holes, which explode due to their inverse temperature-mass relationship, can reach temperatures up to the Planck energy, making them some of the hottest objects in the universe .
Supermassive Black Holes and Coronal Activity
Supermassive black holes, particularly those in active galactic nuclei, host hot plasma regions known as coronae. These coronae can reach temperatures of approximately 10^9 K. The heating mechanism is believed to be magnetic activity, similar to the Sun's corona, although this has not been directly observed. Recent detections of coronal radio synchrotron emissions from nearby Seyfert galaxies support the presence of both thermal and nonthermal electrons in these coronae, contributing to their high temperatures .
Thermodynamic Properties of Black Holes
Black holes exhibit unique thermodynamic properties. They emit thermal radiation at a temperature determined by their surface gravity, as described by the formula involving the surface gravity, Planck's constant, and the speed of light. This emission implies that black holes have a finite entropy, proportional to the surface area of their event horizon. Due to their negative specific heat, black holes cannot maintain stable thermal equilibrium unless the available energy is less than a quarter of their mass .
Conclusion
Black holes, whether primordial, microscopic, or supermassive, are characterized by extremely high temperatures. The formation process, Hawking radiation, and coronal activities all contribute to their thermal properties. These findings underscore the complex and dynamic nature of black holes, making them some of the hottest and most intriguing objects in the universe.
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