A Black Hole in Our Solar System
By: Ella Alderson
Tags: Science, Space, Physics, Cosmos, Universe

There are only gentle signs at first. The outer planets would careen off their usual orbits and on Earth we’d notice the night sky is threaded with the metallic glint of more and more comets as the days go on. The comets have been torn out of their silent beds in the Oort cloud, sent towards the belly of the Solar System where they might strike any planet and rend gaping craters on the rocky surfaces. A black hole moving fast enough will be unaffected by the sun’s gravity and will leave without much more damage than that. But if the sun — that massive gold jewel that makes up the majority of our Solar System’s mass — attracts the black hole, a devastating story begins to unfold.

Lunar and planetary orbits deform into wild, tangled paths with the approach of the black hole. Gravitational effects change the landscape all around us with the Earth quite literally parting in extreme earthquakes and the molten fire of volcanic eruptions. Seasons become extreme as our path around the sun grows closer or further away. The tides shift; we are bound to our home planet which could be sent into the sun to burn. Otherwise the Earth might be pushed into the empty, exotic darkness of the cosmos where our fate will be a stony and suffocating freeze without the heat of our star. Jupiter — larger than the black hole but less massive — will have its thick, brass-colored clouds sucked away and made swirling into a hot and luminous disk.

The black hole continues onto the asteroid belt.

Were life still around, we’d now be able to see the nearing monster and the light bending around it. The black hole is drenched in x-ray radiation from the disk of Jupiter’s gas. If our planet hasn’t streamed either into the sun or into space, we will be consumed by the black hole, unable to see its final meeting with the sun. Our star’s gas and light are stolen into the event horizon and this marks the final wound and death of our Solar System.

A simulation shows the gravitational lensing effects of a black hole passing in front of a galaxy and distorting its light. Image by Urbane Legend.

While black holes can traverse the galaxy and disrupt any star systems in their path, the chances of it happening are fortunately small. This is true especially towards the hem of the galaxy where we reside and where the number of black holes greatly diminishes. A nightmarish scenario like the one above is sensational by nature but unlikely. Instead, the black hole which may exist in our Solar System takes on a very different shape.

Data from half a decade of OGLE (Optical Gravitational Lensing Experiment) revealed a large number of lensing events. During these events objects are magnified by large masses in front of them, providing astronomers with a better view of the more distant objects behind. The survey attempts to detect changes in brightness from distant stars and galaxies. It revealed a strange population of small, nearby lenses in the Milky Way with a mass of .5 to 20 times that of the Earth. This aligns perfectly with predictions of Planet Nine. New research suggests Planet Nine and all its disruptions in our Solar System might not be a planet at all, but something much rarer.

The search for the elusive world known as Planet Nine is based primarily on the behavior of a dozen Trans-Neptunian bodies (objects swirling in the outer reaches of the Solar System, past Neptune). The objects have clustered orbits with similar tilts and at their closest to the sun, they pass by the same area. These orbits are clustered, in theory, due to the gravitational influence of a ninth as-yet-undiscovered planet. The probability that the behavior of the TNOs is pure chance is a paltry 0.007%. Neither can Neptune be the answer since the bodies aren’t close enough to the dense, blue giant. The hypothetical orbit of Planet Nine is seen here with the present day orbit of TNOs. Image by R. Hurt/JPL-Caltech.

There are three ways in which Planet Nine could have entered our Solar System: it could have formed as-is, in its current orbit, or it could have formed within the inner Solar System before being ostracized to its current position as much as 120 billion km (75 billion miles) from the sun. At this distance from any starlight, it becomes difficult to see. Both of these are unlikely. The most favorable scenario involves Planet Nine forming outside the Solar System as a free-floating planet before being drawn in by the gravity of the sun. There is speculation, however, that what the sun captured was a rare kind of black hole.

The chances of the sun having ensnared a free-floating planet are roughly the same as it ensnaring a primordial black hole. The gift of the primordial black holes is that not only would it explain the clustering of the TNOs, but it would also explain the lensing events of the OGLE survey.

Primordial black holes are still only hypothetical, but are believed to have formed less than a second after the brazen eruption of the Big Bang. Quantum fluctuations during this early and tentative time would have caused matter to distribute unevenly with the more densely packed regions collapsing and giving way to the first ancient population of black holes. They would have ornamented the universe long before stars, long before any sparkling galaxy. To this day they would remain compact and countless, but difficult to find due to their distance and lack of light.

A black hole with a mass of Planet Nine (about five times that of Earth) would measure only 9 cm (3.5 inches) across. This is thanks to the black hole’s great density, allowing it to have visible, gravitational effects even at the size of a baseball. Calculations and computer simulations can only, after all, tell us the mass and not the composition of any object responsible for the TNO anomalies. The figure above is to scale for the proposed primordial black hole. Image by Jakub Scholtz and James Unwin.

To find this primordial black hole is possible but, requires a very different route than the one we’ve so far taken. Searching for a planet involves infrared and microwave surveys; searching for a black hole is a little more experimental. As dark matter and its antimatter pair met and annihilated around the black hole they would form a distinctive halo lit by flashes of gamma radiation. The halo would stretch and saunter a billion kilometers (621 million miles) out in every direction. This is about the distance between Earth and Saturn. These gamma rays might be picked up by current technology like the Fermi Gamma Ray Space Telescope, though any moving sources in x-rays and high energy cosmic rays should also be considered.

There are even more exotic theories of what may be stringing the TNOs along in their peculiar paths. What lies at the edges of our Solar System could be something as strange as a Bose star — cool, collected orbs of dark matter that would provide a way to better understand our galaxy and every other. Whatever may be the answer to this mystery — a bizarre star or an undiscovered super-Earth — will be something new and something revolutionary. In this way the story of Planet Nine unfolds like the tale of an approaching black hole, its sweeping presence giving us a chance to be part of something tremendous.