UIC physicist suggests there may be a black hole in our solar system

James Unwin

Earlier astrophysics research has noted that sets of asteroids well beyond the orbit of Neptune, called trans-Neptunian objects, exhibit unusual orbital characteristics. This has been interpreted as evidence of a new astrophysical body in the outer solar system.

Speculation among researchers in the field is that the orbits of these chunks of rock and ice have been influenced by a new planet, which is commonly referred to as Planet 9, that is about five to 15 times larger than Earth.

But, could Planet 9 actually be a small black hole? That is the theory of a new study co-authored by James Unwin, UIC assistant professor of physics.

In a paper posted online to arXiv, Unwin and co-author Jakub Scholtz of the University of Durham in the United Kingdom, showed that the likelihood of capturing a free planet, which is one of the possible explanations for the origin of Planet 9, is very similar to the likelihood of capturing one such black hole, and thus argued that this is a reasonable scenario deserving further consideration.

“We’re not saying that it can’t be a planet,” Unwin said. “We’re saying it need not be a planet and the important point is that this extends the experimental search needed to find this object we believe may be in the outer solar system.”

The researchers point to gravitational anomalies thousands of light-years toward the center of the galaxy that were recently observed by the Optical Gravitational Lensing Experiment, or OGLE, based at the University of Warsaw in Poland.

OGLE reported six microlensing events during which an object bent the light of a star that was under observation. These six unexpected events correspond to objects whose masses are in the range of 5 to 20 times the mass of Earth, such as Primordial Black Holes, which can be thought of as relics of the Big Bang.

Unwin and Scholtz highlighted in their paper that it is “remarkable” that both anomalies point to new objects of mass between 5 to 20 earth masses and argued that the OGLE observation and Planet 9 may be connected.

An important outcome is that it is much harder to look for a black hole than to look for a planet, they note.

While a planet reflects the light from the sun and radiates thermal radiation as well, the black hole alone gives no such radiation. However, Scholtz said it is reasonable to expect a dark matter halo surrounds this black hole.

“If dark matter can annihilate into observable particles, the halo surrounding the black hole would produce high energy photons which could then be observed in searches for X-ray and gamma-ray sources,” he said.