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  • [ ♪ Intro ]

  • 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 Pressureor 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 ]

[ ♪ Intro ]

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ブラックホールの写真の撮り方|サイゾーウーマンニュース (How to Take a Picture of a Black Hole | SciShow News)

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    林宜悉 に公開 2021 年 01 月 14 日
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