How to Understand the Black Hole Image

How to Understand the Black Hole Image


On Wednesday April 10th 2019 you will
probably see the first-ever image of a black hole. That’s when the Event Horizon
Telescope will be releasing their results and I haven’t seen them yet but
I think they’re going to look something like this and I can be relatively
confident because well it’s gonna look a bit like a fuzzy coffee mug stain. But if
you are disappointed by this image I think that misses the gravity of the
situation. From this image we should be able to tell whether the general theory
of relativity accurately predicts what happens in the strong gravity regime
that is what happens around a black hole what I want to do here is understand
what exactly we are seeing in this image so here is my mock black hole of science
and this sphere represents the event horizon. That is the location from which
not even light fired radially away from the black hole could be detected by an
outside observer. All of the world lines end up in the center of the black hole
in the singularity once you’re inside here there is no coming back
not even for light. The radius of the event horizon is known as the
Schwarzschild radius. Now if we were just to look at a black hole with nothing
around it we would not be able to make an image like this because well it would
just absorb all electromagnetic radiation that falls on it but the black
hole that they’re looking at specifically the one in the center of
our Milky Way galaxy, Sagittarius A* has matter around it in an accretion
disk. In this accretion disk there is dust and gas swirling around here very
chaotically it’s incredibly hot we’re talking to millions of degrees and it’s
going really fast a significant fraction of the speed of light and it’s this
matter that the black hole feeds off and gets bigger and bigger over time but
you’ll notice that the accretion disk does not extend all the way in to the
event horizon. Why is that? Well that’s because there is an inner most stable
circular orbit and for matter around a non-spinning black hole
that orbit is at three Schwarzschild radii now in all likelihood the black
hole at the center of our galaxy will be spinning but for simplicity I’m just
considering the non spinning case. You can see my video on spinning black holes
if you want to find out more about that. So this is the innermost orbit for
matter going around the black hole if it goes inside this orbit it very quickly
goes into the center of the black hole and we never hear from it again but
there is something that can orbit closer to the black hole and that is light
because light has no mass it can actually orbit at 1.5 Schwarzschild radii.
Now here i’m representing it with a ring but really this could be in any
orientation so it’s a sphere of photon orbits and if you were standing there of
course you could never go there but if you could you could look forward and
actually see the back of your head because the photons could go around and
complete that orbit. Now the photon sphere is an unstable orbit meaning
eventually either the photons have to spiral into the singularity or spiral
out and head off to infinity now the question I want to answer is what does
this black quote-unquote shadow in the image correspond to in this picture of
what’s actually going on around the black hole. Is it the event horizon? Are
we simply looking at this? or is it the photon sphere? or the inner most stable
circular orbit? Well things are complicated and the reason is this black
hole warps space-time around it which changes the path of light rays so they
don’t just go in straight lines like we normally imagine that they do I mean
they are going in straight lines but space-time is curved so yeah they go in
curves so the best way to think of this is maybe to imagine parallel light rays
coming in from the observer and striking this geometry here. Of course if the
parallel light rays cross the event horizon we’ll never see them again so
they’re gone that will definitely be a dark region but if a light ray comes in
just above the event Rison it too will get bent and end up
crossing the event horizon it ends up in the black hole. Even a light ray coming
in the same distance away as the photon sphere will end up getting warped into
the black hole and curving across the event horizon so in order for you to get
a parallel ray which does not end up in the black hole you actually have to go
out 2.6 radii away if a light ray comes in 2.6 Schwarzschild radii away it will
just graze the photon sphere at its closest approach and then it will go off
to infinity and so the resulting shadow that we get looks like this it is 2.6
times bigger than the event horizon. You say what are we really looking at here?
what is this shadow? well in the center of it is the event horizon. It maps
pretty cleanly onto onto the center of this shadow but if you think about it
light rays going above or below also end up crossing the event horizon just on
the backside. So in fact what we get is the whole back side of the event horizon
mapped onto a ring on this shadow. So looking from our one point in space at
the black hole we actually get to see the entirety of the black hole’s event
horizon. I mean maybe it’s silly to talk about seeing it because it’s completely
black but that really is where the points would map to on this shadow. It
gets weirder than that because the light can come in and go
around the back and say get absorbed in the front you get another image of the
entire horizon next to that and another annular ring and then another one after
that and another one after that and you get basically infinite images of the
event horizon as you approach the edge of this shadow. So what is the first
light that we can see? It is those light rays that come in at just such an angle
that they graze the photon sphere and then end up at our telescopes. And they
produce a shadow which is 2.6 times the size of the event horizon. So this is
roughly what we’d see if we happen to be looking perpendicular to the accretion
disk but more likely we will be looking at some sort of random angle to the
accretion disk. We may be even looking edge-on And in that case do we see this
shadow of the black hole? you might think that we wouldn’t but the truth is
because of the way the black hole warps space-time and bends light rays, we
actually see the back of the accretion disk the way it works is light rays
coming off the accretion disk bend over the top and end up coming to our
telescopes so what we end up seeing is something that looks like that.
Similarly light from the bottom of the accretion disk comes underneath gets
bent underneath the black hole and comes towards us like that and this is where
we get an image that looks something like the interstellar black hole. it gets
even crazier than this because light that comes off the top of the accretion
disk here can go around the back of the black hole graze the photon sphere and
come at the bottom right here producing a very thin ring underneath the shadow.
Similarly light from underneath the accretion disk in the front can go
underneath and around the back and come out over the top which is why we see
this ring of light here. This is what we could see if we were very close to the
black hole, something that looks truly spectacular. One other really important
effect to consider is that the matter in this accretion disk is going very fast,
close to the speed of light and so if it’s coming towards us
it’s gonna look much brighter than if it’s going away. That’s called
relativistic beaming or Doppler beaming and so one side of this accretion disk
is going to look much brighter than the other and that’s why we’re gonna see a
bright spot in our image. So hopefully this gives you an idea of what we’re
really looking at when we look at an image of a black hole if you have any
questions about any of this please leave them in the comments below and I will
likely be making a video for the launch of the first ever image of a black hole
so I’ll try to answer them then. Until then I hope you get
as much enjoyment out of this as I have because this has truly been my obsession
for like the last week. I guess what would be exciting is to watch it over
time how it changes, right? there’s a lot of hope that there are blobs moving around
and you know if you see a blob going round the front and then it goes around the
back but you see it in the back image etc then that’s gonna be kind of
cool

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  1. OK, just over an hour to go! This is the link to the Washington DC National Science Foundation livestream: https://ve42.co/NSFstream
    Click here for links to other live streams (there are several available in different countries): https://ve42.co/EHTstream

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

  3. 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?

  4. 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.

  5. 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! ^^

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

  7. 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)

  8. 🙋🏻‍♂️ 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?

  9. 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"?

  10. Humans and space, like watching your relatives take Bananas and shove them into their nose. I bet you Humans even think what Scientists call Black Holes spin….. and that they have a "side"…..Your NASA seems to think so. Too funny.

  11. Does this mean that if we were to lock at a black hole, do we se earth as it was that many years ago that it took light to travel the distance to, and then back, from the black hole?

  12. No. What you are seeing is actually the glowing part of snoop dog's weed. If you actually saw the real image
    Edit: just kidding.

  13. Как времаюя течет возле черной дыры? Ведь время постоянная неизменная. Разве оно может изменяться возле чернрй дыры?

  14. Thank You for this video! Thanks to you I've just understood the reason why that image is in reality "the shadow" of a black hole.

  15. "I think that misses the GRAVITY of the situation" so good 👏👏👏👏 well done again chap, superbly entertaining and great teaching physics lesson for a damn PhD organic Chemist…

  16. jesus maniac in korea : where is jesus? Does Jesus live in a black hole? i want to live forever in heaven after my death. The pastor tells me to pray unconditionally.

  17. I have a logical independant thinking mind ..im not no different than the next bitch but except for my out of thebox tihnking..This all made excellent sense and i always was skeptic that the "hole" was really a sort of "ball"

  18. 본적도 없고 증명된 적도 없는 것으로 소설 쓰고 있네 ㅋㅋㅋ 과학자들이야 말로 광신도들…

  19. Oh no even this channel got tricked into believing the hype. Credibility lowered. There is no proof of black holes existing. https://www.youtube.com/watch?v=kI14fpM3ouU

  20. 블랙 홀끼리 충돌 하면 어떻게 될까요????

    추측컨대 새로운 은하계가 탄생 한다고 본다

    빛의 속도로 충돌 한다면 상대속도는 빛의 2배 거기에서 뿜어져나오는

    에너지는 블랙홀 무게의 4배

    은하계의 중심에 블랙홀이 있다는건

    블랙홀의 충돌로 은하계의 탄생을 의미 한다

  21. I still don't understand why we see a dark path in the center. Light come from behind or anywhere around blackhole can bent around the photon sphere and fill the dark path on their image, right? Like that one photon at 5:05, if we stand on the left edge of the screen we will see it cover the center, right?

  22. I call this Hawking radiation paradox: If time runs faster outside the event horizon of a black hole than it does inside the black hole, Hawking radiation would evaporate the black hole before enough time has passed inside the black hole for such an event to have occurred. So how is it that a black hole could experience two frames of reference at the same time? There seems to be a real paradox here. If an observer inside a black hole looking out could survive long enough, could she witness hawking radiation evaporate the black hole before enough time in her frame of reference passed for the evaporation to occur?

  23. Laughed at the point where you mention photons slingshooting around black wholes….then I realized, it is really the case apparently….WITH EFFING LIGHT PARTICLES/WAVES not only things wih mass….

  24. Hello, then I have a question: why in your prediction and the real photo we do not see the horizontal line that your demo and the interstellar picture are showing? Normally we should see this horizontal line of light no?! My brain is bugging now

  25. It always bugged me that I could never see more than exactly 50% of an object at any given time. Black hole physics could be the key to properly visualizing 4d perhaps.

  26. The black hole image explanations. 1. Spec of dirt with reflectance corona on the camera lens. 2. Toroidal donut imaged (plasmoid), not a black hole. 3. One petabyte 1E +50 imagery using just 2 MB to see artifacts. 99.999% of the data was thrown out. 4. A processing glitch spot. Not so you say. No problem. Show the same image in 2000 more galaxies. You have one trillion to chose from. Crickets.

  27. Serious question, favorite science guy! =) what happens when smart people (like yourself) use psychedelics? Is it a taboo? Would you understand things from a DPOW? Would it help understanding dimensions etc? As psilocybin gets acceptance, could it be a tool for understanding these headturning things? 4D is quite understandable on certain "drugs", what if, you could get this information out of there? (of course i´ve never done drugs, but "I heard" it feels like theres so much information its like downloading a modern 100 GB game to a 1992-model harddrive…Information is never lost…so..where is it stored? Is it stored in that place that people like Tesla and Einstein had access to? We come up with new awesome things all the time..is this information? Was it information before discovery? Were those rules there before discovery? If they dont catch on, will certain rules be forgotten or not discovered because of lack of perspective and fear of ridicule? Parallell with having to explain electricity and computers to someone in the 15-hundreds kind of thing…

  28. how can you tell a black hole is a black hole and not an eclipsed object in front of a star when you look through a telescope?

  29. Does ageing, wrinkles depend on time?, I mean can I live long if I shift to any exo planet near to a black hole when compared to people on Earth?

  30. فوق العاده بود
    سوالات زیادی که مدتها بود ذهنم رو درگیر کرده بود رو جواب داد .
    تشکر منو پذیرا باشید .
    Impressive !

  31. Leaned a lot from this …
    But one question why is the
    Line crossing the hole radially not shown in your predicted image….as well as the real image….
    Plz explain

  32. From what Dr Robitaille suggests this image is not true. https://www.youtube.com/watch?v=Iz8RRN8rY00

    Personally, the whole black hole thing is based on unsettled science. It assumes stars are gaseous objects with no surface, and as a model, observations have falsified this model. It also assumes that gravity is the dominant driving force in the universe, a belief that was derived when space was believed to be empty, to be void of anything, yet it is not, it is alive with electromagnetism and the electric field is 10^39 times more powerful than gravity.

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