An anonymous reader quotes Forbes:
Conventional theory has it that Planet 9 — our outer solar system’s hypothetical 9th planet — is merely a heretofore undetected planet, likely captured by our solar system at some point over its 4.6 billion year history. But Harvard University astronomers now raise the possibility that orbital evidence for Planet 9 could possibly be the result of a missing link in the decades-long puzzle of dark matter. That is, a hypothetical primordial black hole with a horizon size no larger than a grapefruit, and with a mass 5 to 10 times that of Earth.
In a paper accepted for publication in The Astrophysical Journal Letters, the co-authors argue that observed clustering of extreme trans-Neptunian objects suggest some sort of massive super-earth type body lying on the outer fringes of our solar system. Perhaps as much as 800 astronomical units (Earth-Sun distances) out…

If they exist, such primordial black holes would require new physics and go a long way towards solving the mystery of the universe’s missing mass, or dark matter.

Their argument also constitutes a “new method to search for black holes in the outer solar system based on flares that result from the disruption of intercepted comets,” according to a statement from the Harvard-Smithsonian Center for Astrophysics. The paper was co-authored by Avi Loeb, chair of Harvard’s astronomy department, who points out that “Because black holes are intrinsically dark, the radiation that matter emits on its way to the mouth of the black hole is our only way to illuminate this dark environment.”
And in an explanatory video, Mike Brown, a planetary astronomy professor at CalTech, suggests another way it could be significant. “All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found.”

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Source:: Slashdot