Planets and black holes
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Planets and Black Holes: A Comprehensive Overview
Planet Formation Around Supermassive Black Holes
Dust Growth and Planet Formation
Recent research has revealed that planets can form around supermassive black holes (SMBHs) in active galactic nuclei (AGNs). The process begins with submicron-sized icy dust monomers, which grow into Earth-sized bodies outside the "snow line," several parsecs from SMBHs. Unlike protoplanetary disks, the "radial drift barrier" does not hinder the formation of planetesimals in these environments. Initially, low collision velocities between dust particles promote sticking, leading to a decrease in internal density. When the aggregates reach sizes between 0.1 and 1 cm, collisional compression becomes effective, stabilizing the internal density. Once aggregates grow to 10-100 meters, they decouple from gas turbulence, and the aggregate layer becomes gravitationally unstable, leading to planet formation with masses up to ten times that of Earth. The growth timescale is comparable to the AGN's lifetime, particularly for low-mass SMBHs 15.
Black Holes in the Outer Solar System
Planet Nine Hypothesis
The hypothesis that Planet Nine could be a black hole has gained traction. Researchers have proposed that accretion flares resulting from impacts of small Oort Cloud objects could confirm or rule out this hypothesis. The upcoming Legacy Survey of Space and Time (LSST) observing program is expected to provide definitive evidence within a year. Additionally, LSST could confirm or rule out the existence of trapped planet-mass black holes at the edge of the Oort Cloud, indirectly probing the dark matter fraction in subsolar mass black holes and potentially improving current limits significantly 26.
Primordial Black Holes and Trans-Neptunian Objects
Another intriguing possibility is that the anomalous orbits of trans-Neptunian objects (TNOs) and an excess in microlensing events could be explained by a new population of primordial black holes (PBHs) with masses several times that of Earth. If one of these PBHs were captured by the Solar System, it could alter the orbits of TNOs, aligning with the Planet Nine hypothesis. The probability of capturing a PBH is comparable to that of capturing a free-floating planet. This scenario could be confirmed through annihilation signals from the dark matter microhalo around the PBH .
Life Inside Black Holes
Stable Periodic Orbits
Research suggests that stable periodic planetary orbits exist inside rotating or charged black holes. These orbits, classified as "orbits of the third kind," do not exit the black hole or terminate at the central singularity. The existence domain for these orbits is spacious, potentially allowing for life inside supermassive black holes in galactic nuclei. Advanced civilizations could theoretically inhabit these regions, remaining invisible from the outside. Information from the interiors of black holes could be obtained by observing their white hole counterparts 47.
Conclusion
The intersection of planets and black holes presents a fascinating frontier in astrophysics. From the formation of planets around SMBHs to the potential existence of black holes in our outer solar system, and even the possibility of life inside black holes, these studies challenge and expand our understanding of the universe. Future observations and research will continue to unravel these cosmic mysteries, providing deeper insights into the complex dynamics of planets and black holes.
Sources and full results
Most relevant research papers on this topic
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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