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Already in 1906 Percival Lowell sensed the presence in the solar system of a large planet in a very external orbit, which would disturb the movement of the planets Uranus and Neptune, which were not understood based on the masses of the remaining planets.
Lowell named it Planet X, with X from unknown and not number 10 in Roman, among other things because Pluto was not discovered until 1930, so the planets were 8. This sparked a lot of debate during the late 19th century and early twentieth.
Although later scientific advances were able to explain the anomalies in the movement of Neptune and Uranus, the subsequent discoveries of transneptunian objects put the existence of a new planet, called Planet 9, back in fashion.
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In 1984 the Nemesis hypothesis arises that postulates that planet 9 is actually a failed star, a brown dwarf, with an orbit hundreds of times greater than that of Pluto.
Even the most creative have associated this planet with the planet Nibiru, from which the Anunnaki would come, gods who according to Sumerian mythology, would be the creators of the human race some 450,000 years ago.
Well, to settle all this, a group of scientists have set out to solve the issue once and for all, demonstrating that, in reality, planet 9 is nothing more than a black hole in our outermost solar system.
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To demonstrate this, scientists from Harvard and the "Black Hole Initiative" intend to use the LSST (Legacy Survey of Space and Time) telescope, which will come into operation in Chile in 2022.
In order to locate this black hole, scientists will try to detect the light flashes that some objects in the Oort cloud can produce, when they are engulfed by the black hole.
The Oort cloud is an enormous envelope of the solar system formed by frozen objects that, when passing near the black hole, would be absorbed by it, emitting some flashes in its destruction.
More information:
https://www.ambito.com/informacion-general/ciencia/el-supuesto-planeta-9-del-sistema-solar-podria-ser-realidad-un-agujero-negro-n5117939
https://astronomy.com/news/2020/07/is-planet-nine-a-black-hole-or-a-planet-harvard-scientists-suggest-a-way-to-find-out
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