The hypothetical Planet Nine, theorized to be orbiting somewhere in the outskirts of our solar system, could actually be an ancient black hole.
For decades, scientists have theorized that there is a ninth planet orbiting our Sun. Based on suggestions the planet could be 10 times bigger than Earth and 20 times farther out from the sun than Neptune.
The scientists who predicted the planet’s existence did so based on the strange, highly elliptical orbits of around 30 so-called Trans-Neptunian objects (TNOs). Another weird feature is that the Kuiper Belt – a circumstellar disc full of icy asteroids, comets and dwarf planets which encompasses the solar system – orbits in the opposite direction to the planets within it.
But recently researchers published a paper titled“What if Planet 9 is a Primordial Black Hole?” on arXiv. It suggests that the ninth planet is actually an ancient Primordial black hole (PBH) about the size of a tennis ball.
“We take these objects to be primordial black holes and point out the orbits of TNOs would be altered if one of these PBHs was captured by the Solar System, in line with the Planet 9 hypothesis,” states the paper.
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A lot of scientists accept that this source could be a free-floating planet. But co-authors of the paper, Jakub Scholtz and James Unwin, argue that the PBH scenario is not unreasonable and should be taken into account.
“Capture of a free-floating planet is a leading explanation for the origin of Planet Nine, and we show that the probability of capturing a PBH instead is comparable,” the astronomers wrote in the paper.
PBHs have formed soon after the Big Bang 13.8 billion years ago. Astronomers believe PBHs with the lowest mass have probably evaporated. However, the larger ones may still exist even though we have never directly observed them. Because primordial black holes formed so early on in the existence of the universe, they are much smaller than their modern counterparts.
However, now it could be a very difficult task for scientists to confirm this theory. With a mass of around five Earths and a radius of about five centimeters, the hypothetical PBH would have a Hawking temperature of approximately 0.004 K, making it colder than the cosmic microwave background (CMB). Thus, the power radiated by a typical PBH alone is very small, which makes it pretty hard to detect.
If the hypothetical Planet Nine did turn out to be a black hole, it would also explain why it has been so far impossible to detect as researchers have so far been looking for an object in visible light.
But the researchers now propose examining cosmic rays and gamma rays which could be emanating from the small black hole.