13 votes

I have a basic and possibly uninformed question about the event horizon of a black hole

It is my understanding that if you are looking at an object falling into a black hole from a remote viewpoint, then the object will appear to take “forever” to complete the fall into the black hole. The object is effectively frozen in time at the black hole’s event horizon, from the remote viewer’s POV.

Is this the correct interpretation so far? If so, let’s remember that.

It is also my understanding that a black hole can increase in mass as it captures new objects. The mass does increase from an external viewpoint. Is this accurate?

If I understand known science on the above points, then the paradox I see here is that while the visual information is frozen in time from the external POV, the mass of the black hole does increase from the external POV. So is this where the Holographic Principle comes in? Or is there another explanation here, or am I off-base entirely?

Or is it just that the accretion disk gains mass and black holes never increase in mass from an external POV, after they are initially formed?

Is this known?

Please either attempt to answer my tortured question, or point me to material that might lead me ask a better question.

Thanks!

4 comments

  1. [2]
    Diff
    Link
    I don't have an answer but I do have a link. I liked this answer in particular:

    I don't have an answer but I do have a link.

    I liked this answer in particular:

    The distant observer doesn't see what is going on, so you can't take their word for it. In reality the falling astronaut enters the black hole without noticing anything funny at the event horizon and adds his or her mass to the black hole.

    Even from the distant observer's perspective, one needs to take into account that all physical objects (including light!) have energy. This energy increases the black hole's mass and its event horizon "reaches out" to swallow up the astronaut in a finite time.

    For instance, imagine an electron entering a black hole. It has an mass of 10-31 kg, so it will add around 10-60 km to the black hole event horizon. Assuming a stellar mass black hole with radius around 1 km, the gravitational time dilation at this distance from the event horizon is a factor of around sqrt(1060)=1030. Assuming that the electron is moving at close to the speed of light as it falls in, it takes around 10-54 seconds to cross this distance. For the distant observer, then, the electron enters the event horizon very quickly once it gets to that radius (in 10-24 seconds)! An astronaut would be even faster.

    4 votes
    1. Neverland
      (edited )
      Link Parent
      Well that's a perfect link, and I do like your quote.. Thanks!

      Well that's a perfect link, and I do like your quote.. Thanks!

      1 vote
  2. [2]
    Staross
    Link
    PBS Space Time has a whole serie on that, but I have to say I didn't understood much: https://www.youtube.com/watch?v=qPKj0YnKANw&list=PLsPUh22kYmNCHVpiXDJyAcRJ8gluQtOJR

    PBS Space Time has a whole serie on that, but I have to say I didn't understood much:

    https://www.youtube.com/watch?v=qPKj0YnKANw&list=PLsPUh22kYmNCHVpiXDJyAcRJ8gluQtOJR

    3 votes
    1. firstname
      Link Parent
      what a wonderful channel, after watching one of the episodes it was an easy click on the subscribe button.

      what a wonderful channel, after watching one of the episodes it was an easy click on the subscribe button.

      2 votes