# Black Holes man

1. Nov 28, 2005

### Mr. dude

OK. Black holes. I know they are a super dense thing but made up of what? The remnants of its former stardom? Ash? What is a black hole actually made of? These things facsinate me.

2. Nov 29, 2005

### Chronos

A black hole technically is a spacetime entity that only interacts gravitationally and quantum mechanically with the rest of the universe. It only betrays its existence by tugging at nearby objects [which can produce spectacular fireworks] and weakly squawking by the rules of quantum physics. It has none of the other properties we ascribe to ordinary, unsquished matter.

3. Nov 29, 2005

### Phobos

Staff Emeritus
Matter and energy squished down to a singularity (point). Once reaching that singularity state, it is something totally new (as Chronos described) & just beyond the ability for modern physics to fully explain.

Some form from the collapsed cores of giant stars that went supernova. Some form from the accumulation of lots of matter (e.g., possibly supermassive black holes to be found in the center of many galaxies). Some may have formed directly out of the Big Bang (so-called primordial black holes).

I'm sure we can suggest some excellent links on the subject if you want to study it further.

4. Nov 30, 2005

### Mr. dude

ok. So they are smaller than I thought. Thanks for the help.

5. Nov 30, 2005

### professor

correct me if im wrong, but here is what i have to say on the topic:

the event horizon of the black hole is a great deal larger than its singularity (if this is the sort of black holes we choose to discuss) the singularity is that point at which the gravitational pull of the former, more spread out matter had been pulled into by an infinite (for a degree of distance) gravitational feild..aka the smallest space that the matter could possibly be compacted into is the amount of space it takes up. Though what many referr to when they call somethign a black hole is the outreach of the event horizon, which is the endpoint of the holes infinite strength of gravity. picture a marble with a giant black (chaotic as far as quantum mechanics are concerned) void concealing it. This void could have a diameter anywhere from about the size of the sun to presumabley the size of a small group of solar systems.

6. Nov 30, 2005

### SpaceTiger

Staff Emeritus
In astronomy, what we usually mean by the "size" of a black hole is the extent of its event horizon. For a non-rotating black hole, this is simply:

$$R_{BH}=\frac{2GM}{c^2}$$

For a supermassive black hole, this can be as large as the solar system. For a collapsed star, it's a few kilometers. Primordial black holes can be arbitrarily small, perhaps limited by the planck length. We do expect real black holes to be rotating, but the outer event horizon will still be at the same order of magnitude.

Last edited: Nov 30, 2005
7. Dec 3, 2005

### mars2

en...there is (are) a black hole(s) in every galaxy .the astronomers have found some evidences . Cygnus X-1,maybe,is a black hole .