We tend to think of the solar system as our little corner of the universe, but there are still a lot of things we don’t know about it. For example, what’s perturbing the orbits of small space rocks out past the orbit of Neptune? Some scientists believe there’s another planet out there, often called Planet Nine. What if it’s not a planet, though? Researchers from Harvard University have published a paper that explores the possibility that our solar system is home to a tiny, ancient black hole.
For decades, the solar system had nine official planets, but Pluto was kicked out of the planet club and demoted to dwarf planet status. Astronomers felt that was the only logical conclusion after learning more about other Pluto-like objects far out in the Kuiper Belt, a ring of icy rocks out past Neptune. That also goes to show you how much there still is to learn about this region of space and how a planet, or even a black hole, could be hiding in the void.
Scientists began taking Planet Nine seriously several years ago when researchers from Caltech published compelling evidence that something had nudged the orbits of many Kuiper Belt Objects (KBOs) into alignment. The team suggested a small gas giant roughly ten times Earth’s mass could do the trick, but no one has been able to confirm such a planet exists yet.
Harvard professor Avi Loeb and undergraduate student Amir Siraj contend a small black hole would also account for the effect on KBOs. However, this wouldn’t be your run-of-the-mill stellar-mass black hole but a hypothetical primordial black hole. Today, black holes only form when stars exhaust their nuclear fuel and collapse into a singularity, but in the early universe, scientists speculate that high-density regions of space could have formed smaller singularities without beginning as a star.
A small black hole hanging out in our solar system would be perfectly dark, at least most of the time. Loeb and Siraj say it should be possible to detect such an object by watching for “accretion flares” as small bodies approach the black hole and are torn apart by the gravitational forces. The team believes there would be at least a few of these every year as rocks from the Kuiper Belt and Oort Cloud spiral toward the unseen mass. We might even see these flashes in the next 10 years as the Vera C. Rubin Observatory runs the Legacy Survey of Space and Time (LSST) project. The LSST will scan the entire southern sky every three nights with a wide-angle lens that should be sensitive enough to spot accretion flares.
The primordial black hole hypothesis is admittedly less plausible than a planet or group of small objects causing the orbital anomalies in our solar system. Still, it’s worth investigating. Confirming such an object in our own backyard would be a watershed moment for science.
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- NASA Chief and Jerry Agree: ‘Pluto is a Planet’
- New Study Casts Doubt on Planet Nine Hypothesis