Scientists Are Hunting for Ancient Black Holes Made of Dark Matter

artwork of black holes merging, illustration
Scientists Are Hunting Dark Matter Black HolesMARK GARLICK/SCIENCE PHOTO LIBRARY - Getty Images
  • Researchers have recently pioneered a new way to look for tiny, ancient black holes called primordial black holes, or PBHs.

  • These things have enough gravity to throw off the orbits of objects in our solar system, and even if we couldn’t see the PBHs, we could detect the changes in orbits.

  • Right now, PBHs are theoretical objects, but some scientists believe they could be the key to understanding dark matter.

Rarely in science do we give something a name based on how much we don’t know about it. But that is exactly the case with dark matter. We call it dark because we have no way of using light to look at it, and as such, we know almost nothing about it.

What we do know is that dark matter has gravitational effects—namely, it can bend light around in ways we can detect. Its gravitational affinity is the only sign we’ve had that it’s there at all, and its lead to a lot of theories about what this stuff could be.

The leading theory is that dark matter is made up of Weakly Interacting Massive Particles, or WIMPS. But there’s another theory. Popularized and detailed by Stephen Hawking and associates in the 70s, it proposes that some (or even all) dark matter is contained in what are called primordial black holes (PMBs)—small black holes that theoretically formed immediately after the Big Bang and litter the universe.

The most promising PMBs for this theory are the ones that are about the size of asteroids. The thing is, it’s not exactly easy to find these things either. While we’ve gotten some encouraging results from LIGO and Virgo, we’ve still never seen one for certain. At the moment, they remain theoretical objects.

But recently, in a new and not-yet-peer-reviewed paper from MIT and the University of California Santa Cruz, a group of researchers has proposed a new way to look for these elusive PMBs.

If there are as many as the team thinks there should be, and they interact with gravity as we expect them to, they should be zooming around in a way that some of them should pass close by various objects in our Solar System—including Earth. And if that happens, it should actually be enough to disturb the natural orbits of these objects in a way that we can measure. As the team told LiveScience, if a PBH passes by a planet closely enough (within the distance between the Earth and the Sun), “it starts that planet wobbling or rocking slightly around the path it was taking before the flyby.”

And that is something we can spot.

That rocking will move orbits of closer towards or further away from the Sun very slowly over time. So, the researchers took to the JPL Horizons data base to get information on as many orbital paths as they could. They then ran simulations for each one to see how the orbits would change if a PBH passed by. The results showed that these tiny black holes could shift orbits by inches or even feet.

Now that we know what these things could do, we just have to look for those results to show up in real life to finally spot PBHs for the first time. But “just” is maybe unfair here—that process won’t be easy, even if it turns out to be possible. Using this new method requires incredibly precise measurements of all of the orbits in our Solar System, and we only have data with that kind of accuracy for a few objects, like Mars and the Moon.

But it’s still a new way to look, as long as we can get a better grip on the rest of our Solar System’s orbits in the near future. That’s going to be hard, but if this is the way we finally crack the case of PBHs—and maybe even dark matter—it’s worth pretty much any amount of effort.

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