[ intro ].

Just in case you need something to keep you up at night. we can't see them directly, astronomers estimate our galaxy is peppered with anywhere from ten million to a billion black holes. They're all remnants of stars whose cores collapsed into infinitesimally small points.

And while each is bizarre and braain-bendy in its own way, models tell us that these objects at least have limits. But, then again… our models are sometimes wrong. Like, picture a star with a composition similar to the Sun's, but much bigger.

According to models, the biggest black hole made from a single star like that couldn't exceed twenty-five solar masses. Except… astronomers just found one weighing in at more than twice that. They published their mystery last week in the journal Nature.

And it might require rethinking exactly how massive stars evolve. This black hole was found while astronomers were looking at data from a star about eight times more massive than the Sun. It's called LB-1, and the paper's authors calculated that it's roughly fourteen thousand light-years away.

Based on patterns in the star's light, they found that the star was moving — getting closer to, then farther from Earth over a period of about seventy-nine Earth days. That indicated it was orbiting something. Something the team couldn't detect.

Still, even though they couldn't see the mystery object, they could use data from LB-1 to estimate its mass. And the results were pretty telling. Based on the calculations, the smallest possible mass for this object — just based on how the star was moving — was about six solar masses.

Technically, that means it could be star. But a star that massive would be bright enough for us to detect it. So, instead, the team proposed this companion had to be a black hole.

After analyzing more data, they estimated that the actual mass of this thing is between fifty-five and seventy-nine times the mass of our Sun. And that's where things get messy. Because those numbers are more than twice the mass we thought possible given the black hole's surroundings.

See, both LB-1 and the surrounding area contain a decent amount of elements other than hydrogen and helium. And according to models, single stars can't form huge black holes in that kind of environment. They should lose too much material at the end of their lives.

So if they do become black holes, they should peak around twenty-five solar masses. Not fifty-five to seventy-nine. So this discovery might mean we need to go back and modify our models for how stars evolve.

But it may also mean that something else is going on. For instance, the authors of this paper have suggested that, well, maybe LB-1's black hole didn't come from a single star after all. Maybe, this system used to have three stars — but after one collapsed into a black hole, it ate one of the remaining two.

Alternatively, maybe there are two, less-massive black holes here, and they're orbiting each other so closely that we can't tell them apart. Of course, it could also turn out that the distance measurements of LB-1 are incorrect, since some of the team's data do disagree with other sources. And that would seriously mess up the math.

But regardless of how that plays out, this black hole will still be special. Right now, it's the only stellar-mass black hole we've found that can't be observed in the X-ray part of the electromagnetic spectrum. That means it's not stealing gas off its companion star, and it's not actively consuming matter.

So this discovery could mean there's an entire population of these secret black hole companions, just waiting to be found. In other black holes news, a group of astronomers published a paper last week in The Astrophysical. Journal with evidence that planets — planets! — could apparently form around supermassive black holes.

And I don't mean, like, the black hole's gravity captured them. I mean planets could form around black holes like they do around stars. Just when you think you understand the universe, black holes show up and ruin everything!] It does give me context though,.

I'm glad that our planet is orbiting ‘not a black hole'. According to the paper, the action happens in what's called the circumnuclear disk. This is a thin disk of dust and gas a ways away from the black hole — much farther than the accretion disk that feeds the thing.

Out there, the black hole's gravity isn't overpowering, so particles could collect into a giant ball of rock. But if you're going to make a planet around a black hole, you don't just need distance. Your circumnuclear disk also needs to be dense.

Partly because, well, you need a lot of stuff to make a planet. But also, because you need something to block radiation from the accretion disk. Otherwise, the outer region of the circumnuclear disk will be too hot, and grains of ice and dust won't be able to stay solid and bind together.

In theory, black holes should be able to check these boxes, no problem. But in the new paper, one team decided to actually test this. They applied current models for planetary formation to the circumnuclear disk of a supermassive black hole that was actively eating matter.

And their model generated eighty-five thousand planets, each about ten times the mass of Earth and orbiting at various distances. Admittedly, the planet-making process didn't happen quite like normal. Among other things, the planets took about four hundred million years to form, which is several times longer than what happened in our solar system.

But hey, they formed around a supermassive black hole. It makes sense that things would happen differently. These results are amazing to think about, but they only came from a model.

We're still a very long way from finding planets like this — if they're really out there. After all, it was only this year that we managed to image the shadow of a supermassive black hole. Finding a planet amongst all of that will be way more difficult.

The authors actually point out the usual methods of finding planets are, and I quote, “hopeless.” But there could… maybe… possibly… be something in X-ray or radio wave data. Still, when you think about it, it used to be impossible to detect any planets around other stars — so who knows what we'll be capable of in the future? Thanks for watching this episode of SciShow Space News!

Before you go, we've got two quick announcements for you. First, this episode is brought to you by our President of Space, SR Foxley! SR is one of our patrons on Patreon and is part of the community that keeps SciShow going.

So, thanks for your support! And also! It's December, which means it's calendar-shopping time!

If you're in the market for a 2020 calendar, consider checking out our lunar calendar. It's super satisfying to look at and displays the phase of the moon for every day of the year. So you can always know what's going on up there.

You can find them in our merch shelf below, or at DFTBA.com. [ outro ].