5k views

Why is a black hole black?

In general relativity (ignoring Hawking radiation), why is a black hole black? Why nothing, not even light, can escape from inside a black hole? To make the question simpler, say, why is a ...
4k views

Can we have a black hole without a singularity?

Assuming we have a sufficiently small and massive object such that it's escape velocity is greater than the speed of light, isn't this a black hole? It has an event horizon that light cannot escape, ...
2k views

Why must a singularity form inside a black hole? [duplicate]

What is the exact reason that normal matter can not exist within an event horizon? I can understand how a super-dense object like a neutron star could accrete mass until its physical radius is less ...
2k views

A Hollow Black Hole

I was just reading a question about the gravity inside a hollow neutron star. It was a trivial question, obviously there is no force felt. But then it got me thinking. Suppose you had a hollow sphere ...
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Event Horizon of Supermassive Black Holes

I'm going to ask/explain this as best I can; I'm sure I have some fundamentals wrong here. Spaghettification is a phenomenon which occurs only in stellar-mass black holes owing to the immense gravity ...
195 views

How do we know black hole is empty (except singularity)?

As no information is allowed from inside event horizon, how did we figure out that all matter/energy in a black hole is concentrated at a point like singularity. Say for example how it was ruled out ...
722 views

Dipping a Dyson Ring below the event horizon [duplicate]

The basic assumption about inescapability beyond the Event Horizon is that the necessary escape speed (orbital speed) would exceed speed of light, therefore no object can achieve it. Now, would it be ...
180 views

Thought experiment: ultra-fast outward push inside a black hole

Suppose I have a classical schwarzchild Black hole $B$ of mass $M$. And consider a spherical-subset (or sub-black-hole if you will) $B'$ (sharing the same singularity and having mass $M'$ (We will ...
157 views

Self-collisions in curved space

I know perfectly rigid objects are physically impossible, but let me describe a simple thought experiment that I can't theoretically solve. Imagine you have an almost-closed ring-shaped perfectly ...