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  • In April of 2019, scientists unveiled the first image ever taken of a black hole.

  • The photo of the supermassive black hole M87* was possible thanks to the Event Horizon Telescope,

  • or EHT.

  • Comprised of eight radio telescopes around the world working together, the EHT is effectively

  • a telescope the size of the planet.

  • But M87* may have layers that are yet to be seen, and taking a snapshot may mean extending

  • the EHT's footprint beyond that of Earth.

  • As you probably know, black holes get their name because they're so massive that light

  • that crosses the event horizon can't escape their gravitational pull.

  • They are, by their nature, invisible, so technically we didn't really take a picture of a black

  • hole but rather its shadow.

  • We can, however, see what's outside the event horizon.

  • In fact that area can be very bright, as matter being pulled into the black hole rubs together,

  • gets superheated and gives off electromagnetic radiation.

  • The hottest part of that so-called accretion disk is represented by the orange halo in

  • the famous photo of M87*.

  • Knowing the size of the black hole's shadow against the accretion disk can help determine

  • the mass of the black hole, and currently the EHT is accurate to within about 10%.

  • But between the accretion disk and the black hole's shadow, Einstein's theory of General

  • Relativity predicts there is another layer, called the photon ring.

  • These photons passed the black hole at just the right distance and inclination to orbit

  • it before escaping and reaching an observer.

  • Really the photon ring consists of an infinite stack of subrings, each ring getting sharper

  • and fainter.

  • Photons that have orbited the black hole more belong to higher numbered subrings, so the

  • first subring is made up of photons that have made at least one half an orbit of the black

  • hole.

  • Subring 2 is made up of photons that have made at least one full orbit before escaping,

  • and so on and so forth.

  • Each successive ring is made up of photons that were shot into an exponentially narrower

  • window.

  • Imaging these rings would be yet another feather in Einstein's “I was right about General

  • Relativitycap, which at this point must look like a peacock.

  • It would be the first time we've seen space bent so much that it curves light

  • into complete loops.

  • But they would also give us more useful information about the black hole, providing a better estimate

  • of its mass and telling us information about its spin as well.

  • So, now the question is, how do we go about detecting the photon ring?

  • If we've already made a telescope the size of the whole Earth, what's next?

  • Well, making one bigger than Earth.

  • Obviously.

  • It was once thought that meaningfully upping the EHT's power would require putting many

  • instruments in orbit.

  • But astronomers were surprised by how strong and clear the signals from M87*'s subrings

  • were.

  • They have since proposed that the EHT's resolution could be dramatically increased

  • with just one instrument, even one that's piggybacking on another mission.

  • And the farther away that instrument is, the more powerful the telescope becomes.

  • One placed in low earth orbit could detect the photon ring's first subring.

  • If it was on the moon, detecting the second subring would be possible.

  • Over a vast enough distance, the EHT's resolving power could be increased a hundredfold.

  • My nerd heart is already all aflutter imagining the pictures we could take with a hundred

  • times the power of the telescope that first photographed M87* in 2019.

  • But we may have to wait a bit longer.

  • Even if everything goes well, the EHT may not get a space based component for another

  • decade.

  • Once that's in orbit we'll have our chance to confirm another prediction of general relativity,

  • and see light that walked on the very edge of a black hole.

  • And this time, nobody better say it's blurry.

  • While the EHT may not be expanding into space for a while, there are plans underway to add

  • more earth-based telescopes to its arsenal

  • M87* is also shooting out gigantic jets of matter at almost light speed and we've taken

  • some stunning pictures of those too.

  • For more on them check out my video here.

  • Thanks for watching, be sure to subscribe and I'll see you next time on Seeker.

In April of 2019, scientists unveiled the first image ever taken of a black hole.

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最初のブラックホールの写真が見せなかった隠された現象 (The Hidden Phenomenon the First Black Hole Photo Didn’t Show You)

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    Summer に公開 2021 年 01 月 14 日
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