Remember when scientists were going  to turn on the Large Hadron Collider?

And some people thought it  would make a huge black hole that would swallow up the entire Earth? Luckily that didn’t happen.

And the closest black hole remains a bit farther away than the Franco-Swiss border. It’s not even in our solar system. But on the scale of an entire galaxy, it  might sound a bit too close for comfort.

Because a group of scientists  recently proposed that a few black holes could be hiding  in what's basically our backyard. [♪ INTRO] It’s hard for our puny human minds to  picture just how big space really is. It would take the fastest thing  in the universe about four years to go from our solar system to  Alpha Centauri, the next one over. In other words, it’s about four light years away.

And as far as we know, there’s no  black hole that’s that close to us. But our solar system and Alpha Centauri are  practically sitting on top of one another when you consider the whole Milky Way galaxy. So if you’re looking at our general neighborhood, you’ve got plenty of black holes to choose from.

Or at least it looks that way. Because sometimes, what we think is a  black hole turns out to be something else. For example, in 2020, scientists said they  found a black hole in the system HR6819.

At a mere 1,100 light-years away from us, it would have been the record holder  for “closest known black hole”. But a different science team eventually proved this stellar system had no black hole at all. So why did scientists get fooled?

It turns out, black holes are harder to  find than missing socks in the laundry. On their own, they’re completely invisible. So astronomers have to find them  using other, indirect methods.

For example, they can hunt for light  emitted by stuff around the black hole. If there’s a bunch of gas swirling  around them in a doom spiral, the black hole’s presence will cause that  gas to get so hot it glows in X-rays. Or if the black hole has at  least one companion star, astronomers can infer its presence by watching how that star moves, or how its  light signature changes over time.

And if you want to really get exotic, you  can also use those ripples of space-time called gravitational waves to find black holes. But technically, those ripples  just show something massive is lurking there in the darkness. So many times, the indirect  signs that a black hole may exist turn out to be a  misinterpretation of the data.

But what’s the closest black hole where  the data do seem to be definitive? It’s an object known as Gaia BH1, and it’s  roughly 1,500 light-years away from us! That makes it three times closer  than the previous record-holder, but it’s still over three hundred  times further than Alpha Centauri!

And astronomers are pretty darn sure  this black hole is legit because it wasn’t just one team that discovered it. Two teams discovered Gaia BH1  independently of each other back in 2022. And if two groups can agree on  observations, that’s a home run for science.

If only getting your friends to  agree on a pizza order was that easy. Now as the name suggests, Gaia BH1 was discovered with the the help of a spacecraft called Gaia. And its primary mission is to survey  the whole sky night after night and make super accurate  measurements of where stars are.

This allows Gaia to track stars that  have a strange “wobble” in their motions. That means they have some kind of companion competing in a gravitational tug-of-war. It could be a planet, another  star, or yes, even a black hole.

The more massive the companion is,  and the closer it is to the star, the more influence it will have. In other words, astronomers can  measure the amount of wobble to estimate how massive the companion is. If it’s massive enough to be a star, but  there’s no additional source of light, it’s almost certainly a black hole.

So that’s what astronomers  concluded with Gaia BH1, but it took more observations to confirm it. That finally came when several ground-based  telescopes pulled a superhero team-up and studied the wobbling star using  different scientific instruments. Instead of just watching the star move, they looked at how the color  of its light changed, too.

It’s a phenomenon known as Doppler shift, where the light looks bluer as  the star is moving towards us, and redder as its orbit takes it away. The more extreme the color shift,  the more massive the companion. And this star’s companion was so  massive that, if it had been a star, it would have been 500 times brighter  than the one astronomers could see.

In other words, Gaia BH1 is a black hole. Thanks to Opera for supporting this SciShow video! Opera takes browsing beyond the default.

It’s fully-featured for privacy,  security, and everything you do online, like, for example, watching SciShow! But it is also good for making SciShow. When the SciShow team researches a video topic, we end up with, as you might imagine,  a lot of open tabs for all of the peer-reviewed academic  literature that we sift through.

Opera has a solution for that. Their Tab Islands offer another  approach to research organization. You can arrange and collapse  your open tabs to save space.

And if you are like me and you think you  have enough computer power to sit down and read just one paper and then find  yourself accidentally down a rabbit hole, you’ll probably benefit from Opera’s  battery saver that expands your battery life by up to one hour and can be  turned on with just one click. They also have a free and unlimited  VPN built into the browser so you don’t need to deal with extra  extensions to use the web privately. For everything from tab organization to  AI chat, Opera does things differently.

Download Opera for free at  the link in the description. It turns out, it’s not just  the closest known black hole. It’s also a bit of a weird  one, meaning astronomers aren’t just going to pin a proverbial ribbon  on it and move onto other targets.

For one thing Gaia is a dormant  stellar mass black hole. And “dormant” black holes of  that size are way harder to spot because they’re not actively  feeding off of a companion, throwing out a bunch of x-rays  that our telescopes can see. So it’s a total coincidence that the  closest known black hole to Earth is the kind that’s way less abundant in astronomers’  catalog of known black holes, period.

And it suggests there may be way  more of them in our general vicinity. But the Gaia BH1 system is also weird because, given how close the star and the  black hole get to one another, astronomers can’t figure out why the  star that turned into the black hole didn’t eat its companion and get  torn to shreds in the process. They do have some hypotheses, though.

So a closer examination of the system  may eventually reveal the answer, and provide an updated look  at the nuances of black holes and how they interact with  other astronomical bodies. In the meantime, other astronomers are  on the hunt for even closer black holes. And if Gaia BH1 is down the proverbial block, we may have found multiple black  holes hiding under the porch.

In 2023, a team of astronomers published  the results of some computer simulations they ran to model the Hyades star cluster,  which is roughly 150 light years away. In order for their digital stars to replicate  how the real ones were moving around, they needed to add two or  three black holes to the mix. If the real Hyades cluster  really has any black holes, they’d blow the record for the  closest black hole out of the water.

It’d be 10 times closer to us than Gaia BH1. But can astronomers actually prove it? Well, according to the team  that proposed they exist, observational evidence might be a no-go.

Since these black holes would also be  dormant, you could try to find them through a technique called  gravitational microlensing. It would involve watching the cluster  and waiting for a luminous body… basically a background star…to  pass behind a black hole. Then, the black hole’s gravity will act  like a magnifying glass and temporarily distort the star’s light on its way to us.

The greater and longer the magnification,  the more massive the black hole. Unfortunately, the Hyades cluster isn’t  in a great location for this technique. There aren’t enough background  stars in that patch of sky.

The team also acknowledged searching  for any gravitational waves that the black holes would create as  they accelerated through space. But our modern detectors  aren’t sensitive enough to detect the ripples coming  from black holes that small. So as we’re filming this episode,  the closest black hole is still over a thousand light years away.

But with a little bit of  time, and maybe a lot of luck, that record will eventually be broken. And in the meantime, we can all  thank the Large Hadron Collider for not churning out a mini black hole that would destroy the earth  every time scientists turn it on. [♪ OUTRO]