Theoretical Gravastars Are Even Weirder Than Black Holes
TIL I learned about gravastars (aka a gravitational vacuum star), theoretical objects related to black holes. Both are massive & dense, but instead of a singularity surrounded by an event horizon, gravastars are made up of dark energy surrounded by a extremely thin shell of exotic matter.
The shell of the gravastar is utterly dark and the coldest thing in the universe, only a billionth of a degree above absolute zero. If we look at it in deep infrared, even the cosmic microwave background glows bright in comparison. It is made from an entirely new, unique and extreme matter that is at the very limit of what is physically possible in nature and doesn’t have a name yet. Actually, the shell is so incredibly thin that atoms seem truly gigantic next to it.
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Whenever any idea in physics mentions 'exotic matter' alarms should ring. Exotic matter is the deus ex machina for a fairly large class of physics theories: 'if only this stuff which we have never observed, and which we have good reason to believe can't exist, existed then, whoo, strange and wonderful things can happen'. Yes.
There is a famous theorem in mathematical physics, due to Roger Penrose, which says that singularities are inevitable in general relativity given some conditions, one of which is the weak energy condition, which really says that everyone sees the density of matter as non-negative.
'Exotic matter', therefore, is in this case matter with negative density. It usually is this.
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