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Have read that all the information of a black hole is contained on the Event Horizon. Does that include mass density of interior as a function of position? The shape of an event horizon depends on the mass-energy-charge inside the black hole and possible effects by nearby objects. In principle, the effects of nearby objects can be predicted and subtracted away from whatever behavior the Event horizon experiences.

If the information is on the surface then I'd think it sufficient "space telling matter how to move" to effect local fields without signals from nearby masses effecting the mass at the center of the black hole.

Alternative formulation: Is there a difference between information about mass being stored on the Event Horizon vs. mass being at the event horizon? As I recall, charge distributed on a a straight line has the same field far enough away as some other charge density located on one of its equipotential surfaces. Is that part of what's going on here?

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Are you asking about the viewpoint of the external observer, or somebody inside the black hole?

Because for somebody outside, yes everything about the inside of the black hole is frozen on the event horizon. For an external observer, everything is frozen on the event horizon, and so anything that entered the black hole, must be visible on the event horizon. All the mass density of the black hole is obtainable from looking at the event horizon.

For somebody inside the black hole, it is different. When you enter the black hole, nothing special happens (other then being spagettified, but that is a question of taste if you like spagetti). Other then that, time passes normally for you, and you seem to pass the event horizon like nothing happened, you don't even know you passed it.

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  • $\begingroup$ Suppose mass enters a black hole from a binary partner. Can the radius of the black hole be detected to increase? The mass will never be seen to enter. So I guess it wouldn't. $\endgroup$
    – R. Romero
    Oct 23, 2018 at 1:18
  • $\begingroup$ @R.Romero Yes, the mass will be frozen on the event horizon when viewed from outside. Gravitational lensing will make it possible to tell the radius of the black hole. It will increase. $\endgroup$
    – Árpád Szendrei
    Oct 23, 2018 at 1:20
  • $\begingroup$ So you can never see any new mass enter after initial collapse, but using gravitational lensing you can tell mass has entered since some point in the past? Further that lensing can indicate an increase in radius? Is it possible that objects seen frozenin their approach to the event horizon are eventually swallowed up by an expanding black hole? $\endgroup$
    – R. Romero
    Oct 23, 2018 at 13:29

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