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Unveiling the first-ever image of a black hole [video]

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Re: Unveiling the first-ever image of a black hole [video]

#291

Post by LolWolf »

nonbel wrote: post #267
LolWolf wrote: post #257

Earlier quoted context omitted.

As far as I know K. Bouman [0] was the scientist leading the charge on the image processing/reconstruction. A few of her later papers probably have hints [1, 2] about how this is done, but I haven't seen the official release. [0] http://people.csail.mit.edu/klbouman/ [1] https://arxiv.org/pdf/1903.08832.pdf [2] https://arxiv.org/pdf/1702.07361.pdf

Thanks, I think I added the link to the paper while you were writing this. From skimming it I can't tell the answer to my question though. How do they know what appears "black" in the image is really black vs. relatively black?

If you observe a very wide band of light (e.g., EM radiation) and there is nothing received from those spots, then, for all intents and purposes, the region of that image is black.

Now, if you're asking if, perhaps, the region isn't really black, but rather it's emitting some sort of small radiation relative to the bright region, it would be essentially impossible to know without much higher resolving powers (since it might even be indistinguishable from the background noise generated by the surrounding region). There is no way to really know if it's "perfectly black" vs. "orders of magnitude darker than the surrounding regions."

Re: Unveiling the first-ever image of a black hole [video]

#292

Post by scottie_m »

dangban wrote: post #285

Is this a 2D slice of the actual spherical black hole? Because if a black hole is a sphere, then shouldn't the whole thing be golden?

The black hole is warping spacetime around it in a severe fashion. The innermost (unstable) orbit is called the photon sphere, and light can make several orbits around the hole before either falling in, or going off to infinity. The result is that (depending on the hole’s rotation relative to your point of view) you’re going to see roughly the same image we have today. You’re actually going to see multiple images of the entire hole, stretched around the outer edge, and those images multiplied and distorted again. If you could somehow “stand” by the photon spehere you’d see the back of your own head many many times.

The other factor is that while the event horizon itself is a spheroid, the accretion disk of bright infalling material is not. The horizon is totally black, so it will always look roughly like seeing a disk face-on no matter where you look at it. The accretion disk is a “hoop” that’s stretched and the image is multiplied and distorted by the strong warping of spacetime in the region. As a result you get smeared and repeated views of the entire disk including portion behind the hole in a kind of bent band. Plus the whole thing is subject to strong Doppler beaming hence the bright and dark regions.

Re: Unveiling the first-ever image of a black hole [video]

#293

Post by codesternews »

It's really amazing that human mind can predict and tell the things without even seeing it.

How come we even know and predicted the radius and things far away in galaxy without even seeing it. It's just amazing. Wow it just amazes you that scientist even have predicted the radius of thing and how it work etc.[1]

[1] https://www.youtube.com/watch?v=zUyH3XhpLTo

Re: Unveiling the first-ever image of a black hole [video]

#294

Post by bdamm »

wallace_f wrote: post #230
bdamm wrote: post #212

Earlier quoted context omitted.

The entire video is his description of the reasons for why it'll look like a fuzzy coffee mug stain. It's "fuzzy" because of the low resolution, not because the black hole itself is fuzzy. Undoubtedly there will be work to improve the best quality photograph of a black hole, now that we have one at all.

That's not correct. Around 25% of the video is discussion around the concept of the radius of photon sphere to the event horizon, and what constitutes the light surrounding the photon sphere (one explanation he gives is that there are infinite reflections). Then he spends the last 30% of the video talking about reflections of the acretion disk. This is the theory that he never included in his original prediction, but…

Uh.. It's the reason that the "shadow" is larger than the Schwarzschild radius. He's describing the ratio of the "rim" to the "hole". So while the picture may be fuzzy, there's information in it anyway about what the pictures means relative to how large/spin we think the black hole is. In fact I wish he'd said more about the Doppler effect.

Re: Unveiling the first-ever image of a black hole [video]

#297

Post by jperras »

pavanred wrote: post #275
a_d wrote: post #266

Previous work on this was done for the movie Interstellar. The resolution of the rendering software was so high that team members were able to examine the black hole very closely - Because Gargantua was spinning at almost the speed of light, the rendering showed that spacetime warped into shapes never seen before. This led to the publication of —> https://arxiv.org/abs/1502.03808 Kip Thorne describes his work not thi…

Sean Caroll has a great podcast, mindscape [0]. One of the recent episode featured Kip Thorne as a guest and had some great discussions about Gravitational Waves, Time Travel, and Interstellar [1]. It's a very informative and entertaining podcast, I recommend it. [0] https://www.preposterousuniverse.com/podcast/ [1] https://www.preposterousuniverse.com/podcast/2018/11/26/epis...

Wow, that brings me back. I studied GR under Robert Brandenberger, and we used Caroll's book. What a wonderful text.

Definitely going to listen to his podcast!

Re: Unveiling the first-ever image of a black hole [video]

#298

Post by nonbel »

LolWolf wrote: post #291
nonbel wrote: post #267

Earlier quoted context omitted.

Thanks, I think I added the link to the paper while you were writing this. From skimming it I can't tell the answer to my question though. How do they know what appears "black" in the image is really black vs. relatively black?

If you observe a very wide band of light (e.g., EM radiation) and there is nothing received from those spots, then, for all intents and purposes, the region of that image is black. Now, if you're asking if, perhaps, the region isn't really black, but rather it's emitting some sort of small radiation relative to the bright region, it would be essentially impossible to know without much higher resolving powers (since i…

Makes sense. So I guess they could probably tell us an upper bound on how bright it is.

Re: Unveiling the first-ever image of a black hole [video]

#299

Post by ProAm »

ken wrote: post #192
sus_007 wrote: post #141

Here's an animated explanation of the process by the Event Horizon Telescope. https://youtu.be/hMsNd1W_lmE

Misspeak? This video says it's 4 million times as massive as the sun, but today's press release and Wikipedia article about it both say it's 6.5 billion times as massive.

The black hole at the center of the milky way is 4 million times the mass of our sun, the one in the photograph is much more massive. Im guessing that is what they were referring to.

Re: Unveiling the first-ever image of a black hole [video]

#300

Post by [deleted] »

JumpCrisscross wrote: post #27

Good video that correctly predicted the image and describes why it looks the way it does [1]. TL; DR The dark area is the entire surface of the event horizon, including the side facing away from us, plus some more due to photons missing the event horizon "directly" being drawn in. One side is brighter due to its being Doppler boosted. [1] https://www.youtube.com/watch?v=zUyH3XhpLTo

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