What is the difference between Schwarzchild radius and an event horizon?

Question

The title is pretty much self explanatory, thanks for any help.

Answer 1

In general relativity, event horizon is a general term for a boundary in spacetime, defined with respect to an observer, beyond which events cannot affect the observer. Light emitted beyond the horizon can never reach the observer, and anything that passes through the horizon from the observer's side is never seen again. A black hole is surrounded by an event horizon, for example. This means that an outside observer cannot be affected by anything inside the black hole.

More specific types of horizons include the related but distinct absolute and apparent horizons found around a black hole. Still other distinct notions include the Cauchy and Killing horizon; particle and cosmological horizons relevant to cosmology; and isolated and dynamical horizons important in current black hole research.


The Schwarzschild radius (sometimes inappropriately referred to as the gravitational radius[1]) is a characteristic radius associated with every mass. It is the radius for a given mass where, if that mass could be compressed to fit within that radius, no force could stop it from continuing to collapse into a gravitational singularity. The term is used in physics and astronomy, especially in the theory of gravitation, general relativity. It was found in 1916 by Karl Schwarzschild and results from his discovery of an exact solution for the gravitational field outside a non-rotating, spherically symmetric body (see Schwarzschild metric, which is a solution of the Einstein field equations).

The Schwarzschild radius of an object is proportional to the mass. Accordingly, the Sun has a Schwarzschild radius of approximately 3 km, while the Earth's is only about 9 mm.

An object smaller than its Schwarzschild radius is called a black hole. The surface at the Schwarzschild radius acts as an event horizon in a non-rotating body. (A rotating black hole operates slightly differently.) Neither light nor particles can escape through this surface from the region inside, hence the name "black hole". The Schwarzschild radius of the Supermassive black hole at our Galactic Center is approximately 7.8 million km. The Schwarzschild radius of a sphere with a uniform density equal to the critical density is equal to the radius of the visible universe.

Connie Willis's hard science fiction short story "The Schwarzschild Radius" offers both an accessible and accurate explanation of the phenomenon which makes it surprisingly applicable to not-so-scientific pursuits.[

Answer 2

They are the same. Schwarzchild derived the critical radius from his solution to the field equations of General Relativity for a concentrated point mass, and found that radius at which light cannot escape. For a long time it was felt that this could never be observed, since for known masses, the radius was always inside the radius of the body. Since the discovery of highly dense material and collapsed stars, it is now believed that the radius can exist outside the mass, then the object is called a black hole, and the Schwarzchild radius is the event horizon.

Answer 3

Schwarzschild Radius

Answer 4

The schwarzchild radius and the event horizen represent the same thing.
A body whose surface gravity was such that an orbiting satellite would have to travel at the speed of light
My contention is that black holes do not exist.
However if a black hole could exist it would not be black it would be a sphere glowing dimly in white light.
The glow would be the quantun effect of photons whose velocity varied up and down from the average. The faster photons would spiral out from the surface producing the glow.
However,this may be another nail in the coffins of black holes.
Since the mass and essense of a black hole would be concentrated at the center [unlike a normal celestial body] the orbital velocity below the surface would have to increase [exceed the speed of light] which cannot be.
But this produces another problem; The quantum effect that causes the surface,glow.The slower photons could not could not spiral below the surface,they could not spiral outward and they would not be able maintain an orbit .
I dont have to worry about these slower photons,since black holes do not and cannot exist!

Answer 5

Scwarzchild radius: It is the radius for a given mass where, if that mass could be compressed to fit within that radius, no force could stop it from continuing to collapse into a gravitational singularity.
Event horizon: Event horizon is a general term for a boundary in spacetime, defined with respect to an observer, beyond which events cannot affect the observer.

Answer 6

The Scwarzchild solution to Einstein's equation describes a non-rotating black hole. The Scharzchild radius is the radius of the event horizon for this particular solution. However, there are other situations where a 'horizon' exists (the Kerr solution for a rotating black hole, for example) where the solution is not spherically symmetric, so no one radius describes the even horizon. So the Scharzchild radius is essentially an event horizon for one particular situation.

Answer 7

The Schwarzchild radius is the location of the event horizon of a black hole (it has nothing to do with the size of the black hole itself). An event horizon, however, need not be associated with a black hole - it can have other origins.