Black Holes and Planets

Life Imitates Art?

Remember the movie Interstellar? It portrayed an adventure involving a black hole, some planets, and an intrepid crew who traveled via the black hole to rescue some scientists on the “other side”. While it had some obvious gaffes in the story, the science was more or less vetted by physicist Kip Thorne. He described his thought process in the book The Science of Interstellar, which I bought as soon as I got home from the movie. It was interesting to read about the interactions he had with the filmmakers, as well as the decisions he had to make to help them tell their story. ‘

One of the planets in the movie is situated near a black hole, and that proximity alters time and space not just for the region around the singularity, but for the planet itself. Dr. Thorne finds a way to scientifically justify the action on and near the planet, which makes the story all the more interesting.

Could a Planet and Black Holes Co-Exist?

I thought about that book when I saw a recent story about Japanese astronomers postulating the formation of planets around black holes. At first glance, I thought, “That’s gotta be impossible.” But, as it turns out, the possibility of planets forming around such monsters isn’t all that far-fetched. I’m a sucker for black holes (excuse the pun) because they’re just such fascinating objects. It’s why I notice stories about them and often write about these monsters.

Think about what you need to form planets: a cloud of dust and gas and an energy source. Throw in some magnetic field action, and other activities that would stir up a disk of material and you have a planet-making machine. Of course, all the planets we KNOW about have formed around stars. But, nothing says they can’t form in other places with the proper materials. And, that, according to professor Eiichiro Kokubo of the National Astronomical Observatory of Japan, could result in tens of thousands of massive planets orbiting safely outside the event horizon of a black hole. How massive? Probably ten times the mass of planet Earth, according to the professor.

Black Holes and Planets, Oh My

What kind of black holes could support such planet-building activity? In the computer models that Professor Kokubo did, supermassive black holes are good candidates. Some of them are surrounded by disks that could have a hundred thousand solar masses of dust. To put it in perspective, that is about a billion times the dust mass of a typical protoplanetary disk.

Conditions around the black hole do, of course, have to be supportive of planetary formation. In a typical protoplanetary disk, planet formation takes place in low-temperature regions where icy dust grains collide and stick together. They make sort of “fluffy” clumps that eventually collide to make bigger “pieces” of planets. The process continues to make bigger and bigger objects until planets are born.

So, could such a region exist around a black hole? Probably so. Here’s why. First of all, the central region around a black hole emits a large amount of energy. And, you’d think that radiation would destroy any chances for planets to form. However, the dust disk is very dense, and that can block the radiation. So, Kokuba and the team of researchers at NAOJ applied typical planetary formation theory to those black hole disks and it turns out it could work!

The models show that low-temperature regions could exist where ices could exist. Those places could allow the formation of those “fluffy” clumps that are the seeds of planetary formation. If it actually works, planets could form in a few hundred million years.

Black Holes and Planets and Possibilities

Nobody has found those planets yet, but theoretically, they could exist — and I would bet, in reality, they’re out there. It could be the start of a new section of planetary science, which would be pretty cool. The next thing to think about is what those planets would be like? Would they be able to support life? All interesting things to consider!

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