For several years, astronomers and cosmologists have theorized about the existence of an additional planet with a mass 10 times greater than that of Earth, situated in the outermost regions of the solar system. This hypothetical planet, dubbed Planet 9, could be the source of gravitational effects that would explain the unusual patterns in the orbits of trans-Neptunian objects (TNOs) highlighted by existing cosmological data. TNOs are celestial bodies that orbit the sun and are located beyond Neptune.

Building on studies conducted over the past few years, Jakub Scholtz and James Unwin, two researchers at Durham University and the University of Illinois at Chicago, have recently carried out an investigation exploring the possibility that Planet 9 is a primordial black hole. Their paper, published in Physical Review Letters, hypothesizes that the anomalous orbits of TNOs and an excess in microlensing events observed in the 5-year Optical Gravitational Lensing Experiment (OGLE) dataset could be simultaneously explained by the existence of a specific population of astrophysical bodies (one of which would be Planet 9). More specifically, it introduces the idea that Planet 9 and the rest of these bodies may be primordial black holes (PBHs).

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