Is it a hidden planet, or is there a black hole in our back yard?
Even before Pluto was demoted from “planet” to “dwarf planet” back in 2006, astronomers had been looking for another, massive, object out beyond Pluto’s orbit.
The reason is simple: There’s something out there that’s messing with the orbits of known objects in the outer solar system. We can’t see it, but, because it’s pushing things around, we know it’s there.
(Neptune and Pluto were both discovered by astronomers looking for the cause of similar disturbances in the orbit of Uranus.)
Of course, the outer solar system is dark. Very little sunlight reaches it, and lots of the objects out there are covered in dark materials that reflect very little of the light that actually reaches them. Also, it’s cold out there, with almost no heat being radiated by those objects. So, it’s sort of like looking for an icy black cat in a coal mine. Tricky.
Still, based on the amount of gravitational influence this thing has, it’s pretty big…somewhere between 5 and 15 times the mass of Earth! You’d think something that size would be visible to at least one of the many satellites that have been looking for it over the years. Unless, of course, it’s not a planet at all.
That Got Dark Quickly
Several weeks ago, a couple of scientists published a paper that caused quite a stir. What if, they asked, Planet 9 isn’t a planet at all? What if it’s a black hole? Better yet, what if it’s a primordial black hole?
Now, most of us are familiar with the concept of a black hole. Basically, a black hole happens when a star’s nuclear fuel gets spent, and it collapses under its own gravity. The resulting object is so compact and has a gravitational field so intense that nothing can escape it, not even light.
This type of black hole, what you might think of as a “traditional” black hole, is massive. Typically it’s at least 10 times as massive as our Sun. Super-massive black holes, like the ones we think are at the center of almost every galaxy, can be millions or even billions of times more massive than that!
And, contrary to popular belief, a black hole isn’t a dimensionless “point” in space; they have width and volume and a generally spherical shape that can be millions of kilometers wide.
So, why then wouldn’t we be able to spot a black hole at the edge of our own solar system?
Well, here’s the thing: while we’re used to studying black holes with these stellar masses, in truth, pretty much anything can become a black hole if you compress it enough!
You could, for example, take a typical person, compress them, and turn them into a black hole! However, since you started with a relatively small amount of mass, the resulting black hole would be correspondingly small. For a typical person, the resulting black hole would have a radius of about 1.04 ×10−25 m. So, yeah, very tiny.
A “primordial” black hole is basically one of these tiny black holes, possibly left over from the creation of the universe and formed from a relatively small “knot” of matter that collapsed quickly after the Big Bang. In this case, that “tiny” black hole would have a mass about 5 to 15 times that of the Earth, and be about the size of a grapefruit.
So, let’s see. Tiny. Dark. Swallows light…yeah, that would be very tough to spot all the way out past Pluto.
Still, it’s important to remember that all of this is speculation and hypothesis. We’ve never seen any black holes this small, and don’t even really know how such a thing would form. (My “knot of matter” hypothesis is just that, a hypothesis.) In all likelihood, Planet 9 is just another very dark ball of rock and ice, waiting to be glimpsed by some next-generation camera.
The only way to be sure, of course, is to keep looking! Black hole, icy Super-Earth, or killer alien battle station…who knows what we’ll find along the way!
Steven W. Disbrow is the proprietor of “Improv Chattanooga” on the South Side of town. He also creates e-commerce systems and reads comic books when he’s not on stage acting like a fool.