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On April 10th, 2019 the world saw, for the first time ever, visual confirmation that black holes actually exist. Technically, up until now they only existed in theory.

We were pretty sure they were there based on stuff like stars with weird orbits at the center of our galaxy, and really strong radio and other electromagnetic signals coming from really small points in space. But we never actually saw one. Which is why it made such a big splash when researchers released this image of M87*, the supermassive black hole at the center of the galaxy M87, 55 million light years away from Earth.

It's all thanks to the Event Horizon Telescope, or EHT, a collaboration of over 200 individuals spanning 13 institutions and the globe. Last week, they published their findings in six papers in The Astrophysical Journal Letters. In this now famous fuzzy photo, we can't actually see the black hole of course.

Or, rather, its event horizon, the final point of no return for light and matter. The black shadowy blob at the center is actually about 2.5 times bigger than the event horizon. That's as close as the laws of physics will let us get.

Turns out it's hard to take a picture of something that light cannot escape from. Now to snap this picture, we needed a telescope with a resolution of 2,500 times better than the Hubble Space Telescope. In astronomy, angular resolution refers to the ability to see two objects that appear close together in space as their own distinct sources.

But it really just comes down to how much detail you get in to an image. And there are really only two ways to improve it. One is to study light that has a shorter wavelength.

The other is to make your telescope bigger, specifically, increase its collection area, or the size of whatever it uses to collect light. Radio waves are really the best waves to use for studying supermassive black holes, because that's where they, or rather, the material around them, emit most of their light. Also, longer wavelength light does better at penetrating all that gas and dust between us and what we're trying to look at.

So to study a black hole like this, astronomers are interested in radio wavelengths of about 1 millimeter. But there's a catch. At those wavelengths, the telescope you need to resolve a black hole would have to be, like, as big as a planet.

So the EHT collaboration came up with one. They turned the entire Earth into a telescope. Now, just ‘cause you didn't notice any construction in your particular backyard, that doesn't mean it didn't happen.

Here's a weird thing about telescopes: you can take a bunch of small ones, spread them out, and get computers to link them all up, and pretend to have a telescope that's as big as the distance between them. And this actually works. You get gaps in the images, but the same amount of resolution.

This technique is called interferometry. Say you have two telescope dishes spaced a kilometer apart. They're both pointed at the same target in the sky.

Light coming from that source is going to hit the two at slightly different times, but if you have super accurate clocks to keep track of that, you can combine the two signals. The light waves from the two telescopes will interfere with one another, like ripples from two different sources in a pond. But with some sophisticated computer programs, you can use that interference to generate an image.

And suddenly, it's like you had one dish a kilometer across. The more telescopes you have, the more complex it gets, but the better your image will be. To create the EHT, astronomers had to upgrade, link, and synchronize eight pre-existing telescopes around the world, from Hawai'i to Spain to Antarctica.

They collected petabytes worth of data, which was flown on hard drives to supercomputers in the US and Germany to be processed into a picture. Which requires the programs not to just stitch together separate images, but eliminate all the noise coming from stuff that's not the black hole, and then to fill in all the gaps due to us not having a single telescope dish the size of a planet. Filling in those gaps is kind of like inferring the melody of a well-known song when you can only hear some of the notes.

But it might be difficult to narrow it down to just one song. Like, maybe it's “Under Pressure” or maybe it's “Ice Ice Baby.” That's why EHT didn't produce just one image. Initially, there were actually four.

Four separate teams worked independently from one another to produce the first images to avoid potential bias. They used two different classes of algorithms, but in the end they all came out relatively the same. Most importantly, you can see the shadow in the middle of all of them.

That proved their techniques were working. After some more refinement, the now-famous final image was made by averaging three different processing methods. And the Internet, rightly, went wild.

We are, like, way late to this party. Sorry. Now in the future, there are several ways to improve images like these.

One is to simply look at the object for longer. The collaboration observed M87* over 4 nights, between 7 and 25 times each night, collecting data for just three to seven minutes apiece. Another is to collect data at other wavelengths of light, which will require upgraded technology with faster processing speeds.

We could also add in more telescopes, as well as add ones that have larger collecting dishes. Which EHT is working on. Naturally, astronomers want to apply this method to study other supermassive black holes.

Like Sagittarius A*, the strong radio source at the center of our galaxy, the Milky Way. It's also about a thousand times less massive than M87*, but way, way closer. But it's hiding behind a lot of stuff that will interfere with the signal we receive, which future observations will need to account for.

The first ever black hole picture took the internet by storm. But when you understand how much work went into making it, and how many talented scientists were involved, and how they turned our planet into a telescope? It only gets cooler.

Thanks for watching this episode of SciShow Space News, which we couldn't make without the support of our patrons. If you like what we do here, and you're interested in being a part of it, check out patreon.com/scishow. [ ♪ Outro ].