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Black Holes and Optics

  1. Mar 1, 2009 #1
    I had a conversation with a friend about Black Hole images. I showed him a picture of a black hole taken by the Hubble telescope shown here:


    He claims that it's not a direct image of a black hole because we can't see black holes directly. That is merely the matter surrounding it that has been affected by the gravitational pull.

    I believe that it is an actual image of a black hole. Objects require some source of light or medium to form an image. Without these mediums there would be no images so I contend that there is no such thing as a "direct image."

    So is that an image of a black hole?
  2. jcsd
  3. Mar 1, 2009 #2
    By your own source, the black hole is only light-minutes in size whereas that image is of something else that is light-centuries in size.

    Moreover, of course you can have a direct image of a black hole, can you not photograph a shadow or silhouette?
  4. Mar 2, 2009 #3
    It is a black hole indeed, but if you were to look through a telescope to that area of space, you would not see anything. That is why we use special telescopes and computers to be able to spot the radiation and energy emitted from the black hole.
  5. Mar 3, 2009 #4
    its probably an xray or some kind of thermal photograph.

    also how does a black hole weigh anything since it is not made of anything but gravity? or is it just the total mass of everything being sucked in?
  6. Mar 3, 2009 #5
    Black holes are former stars that have gone supernova, in which the core of the star has collapsed into what we call i singularity. A black hole doesn't have mass pre-se, but it is this singularity that we measure.
  7. Mar 3, 2009 #6
    Black holes do have mass. The mass is how you determine the Schwarzschild radius. Black holes are nothing more than very dense matter.
  8. Mar 3, 2009 #7
    dtmmfam.. http://hubblesite.org/newscenter/arc...95/47/image/a/
    I liked the picture, quite good quality. I wish we have an even better telescope. Scientists say the BH core, the serious part is relatively small, so the bright lights around should come from materials around, but the image will change depending on the observing angle, because the materials will orbit the BH mostly in a plane like our planets do the sun, but those materials are very fast moving and so can collide each other violently.
    Last edited: Mar 3, 2009
  9. Mar 3, 2009 #8


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    Staff: Mentor

    I basically agree, though as a practical matter, the first thing makes the second unlikely. However, I'm wondering if anyone has run a simulation of what it would look like if a black hole passed in front of a star and we had front row tickets. Would it look anything like an eclipse or would gravitational lensing cause the star to be so distorted you really can't see a "shadow" of the black hole?

    That said, I don't think we would include the requirement that a disk is visible if the question was applied to stars...
  10. Mar 4, 2009 #9
    I agree that that we cannot see black holes directly because they don't emit visible light. The question of whether we can see an image of a black hole is debatable, and i believe it becomes a metaphysical question.

    It's similar to "if a tree falls and no one is around to hear it, does it make a sound?"
  11. Mar 4, 2009 #10
    http://dspace.anu.edu.au/handle/1885/43269" [Broken] in fact you only had to look as far as wikipedia or google..

    The distinguishing feature is not just the event horizon's silhouette but also the prominent first Einstein ring.
    Last edited by a moderator: May 4, 2017
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