How to Understand the Black Hole Image

We have just seen the first image of a black hole, the supermassive black hole in the galaxy M87 with a mass 6.5 billion times that of our sun. 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
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
Like him, I’m hoping (predicting?) we’ll see some moving images of black holes tomorrow
Prof. Rana Adhikari
Riccardo Antonelli – for excellent images of black holes, simulations and ray-tracing code, check out:
The Event Horizon Telescope Collaboration
Check out their resources and get your local link for the livestream here:
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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38 thoughts on “How to Understand the Black Hole Image

  1. OK, just over an hour to go! This is the link to the Washington DC National Science Foundation livestream:
    Click here for links to other live streams (there are several available in different countries):

  2. Hi, very nice explanation. I have some questions, are the black holes 3D objects? What we see if we are in the back, same if we are in "front"?

  3. 🙋🏻‍♂️ Hello Derrick, I have a question I'd love you to explain! I understand that the gravity past the event horizon of a black hole is so strong that nothing, not even light, can escape it. But in the 70s, Stephen Hawking theorised that black holes radiate energy, until they finally evaporate, by way of quantum processes ("Hawking Radiation"). I'm not a physicist, and to me these two ideas seem contradictory. Radiation would have to be massless, like light, or have mass, like all other fundamental quantum particles, so how can energy in any form escape the singularity's gravity? Could you please do a video about Hawking's Radiation?

  4. I know I'm kinda late but, if we could look at that thin line of light underneath or above the event horizon, the light particles that nearly are captured but released from it's gravity, could we not zoom in far enough on that ring of light to see our past under the right circumstances? (Distance being a huge obstacle)

  5. 👎Тошнило от рекламы перед роликом, но от самого ролика стошнило на много обильнее… хорош фуфло тюхать

  6. Wow, I was doing a research paper on black holes and I started at a paragraph, but this video made my paper almost an entire paper long! Thank you for this! ^^

  7. How can a black hole keep light from escaping since the speed of light is constant and has no mass to be pulled in? Please explain.

  8. Hello. You stated that light could not escape the immense pull of the black hole, but you also stated that it could escape orbit and shoot out into infinity. Could you please clarify?

  9. Почему ролик называется по русски а я при этом нихуя не понимаю о чём речь?

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