How to Understand the Image of a Black Hole

How to Understand the Image of a Black Hole

We are about to see the first image of a black hole, the supermassive black hole Sagittarius A* at the center of the Milky Way galaxy. But what is that image really showing us?

This is an awesome paper on the topic by J.P. Luminet:
Image of a spherical black hole with thin accretion disk
Astronomy and Astrophysics, vol. 75, no. 1-2, May 1979, p. 228-235
https://ve42.co/luminet

Using my every day intuition I wondered: will we see the “shadow” of the black hole even if we’re looking edge on at the accretion disk? The answer is yes because the black hole warps space-time, so even if we wouldn’t normally be able to see the back of the accretion disk, we can in this case because its light is bent up and over the black hole. Similarly we can see light from the bottom of the back of the accretion disk because it’s bent under the bottom of the black hole. Plus there are additional images from light that does a half turn around the black hole leading to the inner rings.

What about the black hole “shadow” itself? Well initially I thought it can’t be an image of the event horizon because it’s so much bigger (2.6 times bigger). But if you trace back the rays, you find that for every point in the shadow, there is a corresponding ray that traces back to the event horizon. So in fact from our one observing location, we see all sides of the event horizon simultaneously! In fact infinitely many of these images, accounting for the virtually infinite number of times a photon can orbit the black hole before falling in. The edge of the shadow is due to the photon sphere – the radius at which light goes around in closed orbits. If a light ray coming in at an oblique angle just skims the photon sphere and then travels on to our telescopes, that is the closest ‘impact parameter’ possible, and it occurs at sqrt(27)/2*r_s

Huge thanks to:
Prof. Geraint Lewis
University of Sydney https://ve42.co/gfl
Like him, I’m hoping (predicting?) we’ll see some moving images of black holes tomorrow

Prof. Rana Adhikari
Caltech https://ve42.co/Rana

Riccardo Antonelli – for excellent images of black holes, simulations and ray-tracing code, check out:
https://ve42.co/rantonels

The Event Horizon Telescope Collaboration
Check out their resources and get your local link for the livestream here: https://ve42.co/EHT

Special thanks to Patreon supporters:
Donal Botkin, Michael Krugman, Ron Neal, Stan Presolski, Terrance Shepherd, Penward Rhyme

Filming by Raquel Nuno
Animation by Maria Raykova

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56 Responses

  1. Stefano Morandi says:

    MIND BLOWN!
    so happy that i watched this video BEFORE watching the actual image, now the hype is 10x!

  2. Mukund Bhanot says:

    what if we look inside the black hole…
    *and Matthew McConaughey looks back at us*
    “Alright, alright, alright…”

    • Mad Dog says:

      Muuuuuuurphhh

    • Mukund Bhanot says:

      okay guys, i did my research on this @Joe Chang fellow here. He’s pretty much a conspiracy theorist spreading lies and false information on the internet, and the platform of his choice is Quora.

      WHAT I DO NOT UNDERSTAND ABOUT THIS GUY IS WHY IS HE REPLYING TO MY COMMENT TO PREACH BS? Seriously dude, join a club or something. Or better yet cancel your internet subscription and walk of the edge of the earth because it is most certainly flat. AMMIRITE? XD
      (I am warning you, do not see his profile. You will start questioning reality itself. 😉 )

    • Real says:

      Hears: Alright, Alright Alright!

      Instantly replies:
      Let’s see what we got… Hive! Bring a sword!

    • Mad Dog says:

      +Joe Chang that’s some timecube level shitposting right there.

    • Volvox says:

      +Joe Chang you takin about the Doom Slayer bruh?

  3. Gubzs says:

    Scientists end up releasing a blank purely white image with the title “Oops! All Photons!!”

  4. Rohum Sahil says:

    Derek: Hey are you excited to see the new black hole image?
    Michael: But…what is an image?
    Derek: (Face palms)

  5. Kaustubh Gupta says:

    Beautiful…
    Physics is love❤️❤️

  6. Kean Giledaks says:

    Amazingly edible video, great visualizations and pacing, thanks!

  7. Chaitanya Singh says:

    I totally forgot about the accretion disk! Thanks for reminding

    This event is on the top list to witness, with the likes of (hopefully and Fortunately) Betelguese going supernova, I’m super pumped

  8. Ibakon Ferba says:

    I did not even know that we are about to take a picture of “our” Black Hole 😮 this is freaking exciting!!!

    • Hector Athan says:

      Well you’re lucky cause I’ve been waiting for 2 years since I first learned about the whole situation….

  9. Tsihoarana Randimbivololon says:

    “Misses the gravity of the situation” pun clearly intended

  10. J.B. Dazen says:

    All I could think while watching your installation was: ¯_(ツ)_/¯

  11. Nicu Stoian says:

    The first image of a black hole will be my best birthday present on april 10th 🙂

  12. Thriller 77 says:

    Doesn’t that mean we’re seeing the shadow in actual three dimensions

  13. Zaeem Atif says:

    Damn amazing…loved it most when you visualised with the graphic picture of a black whole(7:36)….!!!!!

  14. The Exoplanets Channel says:

    Can’t wait to see that image !

  15. Joel Witherspoon says:

    Thank you! I had difficulty understanding accreditation disks and event horizons. You’ve explained it well

  16. Nice Jungle says:

    That’s the most epic explanation about black hole picture I’ve ever seen : AWESOME !

  17. Sasan Amari-Amir says:

    30 sec in, I realize Hawking missed this image 😕

  18. Guillermo M. Serrano says:

    8 days late for April Fool’s Day. Wait, that was me being late.
    ._.

  19. Andrew Kovnat says:

    The universe “simulator” Space Engine quite accurately depicts black holes in this manner, and live! I suggest looking up a recent video of a black hole in Space Engine. Crazy stuff!

  20. William Shreckengost says:

    Black holes: “Neat.”
    The prop work in this video: “OH MY GOD, THAT’S AMAZING!”

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