Question: What is a wormhole? Do they exist independently (like I have heard that black holes lead to wormholes)? A black hole form when stars collapse onto themselves...what will happen if a huge black hole collapses into itself?

Jack Miller answered on 26 Jun 2013:

Hi Sanaban,

A wormhole is a hypothetical bridge through the structure of spacetime, connecting one region for another. As Wikipedia says, for a simple visual explanation of a wormhole, consider spacetime visualized as a two-dimensional (2D) surface. If this surface is folded along a third dimension, it allows one to picture a wormhole “bridge”. (Please note, though, that this is merely a visualization displayed to convey an essentially unvisualisable structure existing in 4 or more dimensions).

The reason wormholes are dealt as something other than science fiction is because they satisfy the Einstein field equations of general relativity. However, wormholes that come about in a black-hole fashion would decay too quickly to be useful. A transversable wormhole, one that is stable, would only be possible if stabilised by exotic matter, with a negative energy density — which is still firmly in the realms of science fiction, for now. There’s a lot of good, readable information on wormholes on the wikipedia article (http://en.wikipedia.org/wiki/Wormhole)

Black holes don’t collapse on themselves — they’re already the most dense known form of matter, so they just get bigger. As their mass increases, so does their surface area, and that increases the rate at which they lose energy through Hawking radiation. Eventually, it’s believe you reach a maximum-possible black hole size, where a larger black hole will never form in nature as the pressure from all this Hawking radiation is sufficient to blow away the clouds of gas that would otherwise feed it, thus limiting its size.

Hope that helps!

— Jack