# Black hole.

1. Apr 23, 2007

### andrewking

Black hole................

Hi I am Andrews, I want to learn about black hole and its gravity where I can collect information about black hole. If anyone knows about the site or about it reply me

2. Apr 23, 2007

### Mk

3. Apr 24, 2007

### andrewking

Thanks for your reply.I have another question about black hole.Is there any exist for black hole,if you know about it shre the information with me

4. Apr 25, 2007

### Mentz114

There is strong indirect evidence for the existence of large black holes at the centre of some galaxies.

5. May 3, 2007

### u83rn00b

did u no if a black hole came into contact wth the earth, all our molecules would expand causeing us to all be strechted out. for example, ud be like 20 yards tall, ur hands would be waaayyy up ther! wut a cool way to die.

6. May 4, 2007

### fasterthanjoao

Sort of. The intense gravitational field would rip us apart (very quickly you wouldn't have any....... recognizable human features left!) and we'd be peeled down to another single layer of atoms on the 'surface' of the black hole.

7. May 9, 2007

Aren't black holes molecular in size? what is, if any, the difference between the size of black holes. If more material is absorbed, then more gravity is possible, therefore the hole gets smaller but denser.

8. May 9, 2007

### Staff: Mentor

It can be useful to talk about the radius of the event horizon as being a "size" since we don't really know what is going on inside it and it generally doesn't matter anyway.

9. May 10, 2007

### josht

There is also a book by Stephen Hawking called The Cambridge Lectures which has a couple of GREAT lectures on Black Holes.

10. May 11, 2007

### bassplayer142

How could a black hole be molecular in size. I understand the great gravity pulling in on the particles but wouldn't they only be compressed to the plank length?

11. May 18, 2007

### lionell

Yes, but black holes also stretch light rays. We would look red all over!
You are right about one thing, it's a cool way to die.

12. May 18, 2007

### MeJennifer

I really don't see any physical meaning of size here.

What's the meaning of size for an ant that sits on a deflating balloon when it has deflated to a point?

Last edited: May 18, 2007
13. May 18, 2007

### Wallace

I think that is Russ's point MJ, that it's pointless to try and talk about the size of the 'singularity', but what you can talk about for black holes is the radius of the event horizon, which does depend on the black hole mass and hence allows black holes of different 'sizes'.

I think you'll find you are actually agreeing with Russ.

14. May 18, 2007

### MeJennifer

My point is that that the r-coordinate in the usual Schwarzschild coordinate chart does not represent a radial or any other physical distance. For instance the size of a black hole is most definitly not $\frac{4}{3} \pi r^3$.

Last edited: May 18, 2007
15. May 18, 2007

### Wallace

Semantics!

16. May 19, 2007

### lionell

What?! Sementics?

17. May 19, 2007

### lionell

What?! No, I mean what does that mean?

18. May 19, 2007

### lionell

What?! No, I mean what does that mean?

19. May 20, 2007

### Wallace

From Dictionary.com:

Semantics is commonly used to refer to a trivial point or distinction that revolves around mere words rather than significant issues: “To argue whether the medication killed the patient or contributed to her death is to argue over semantics.”

20. May 23, 2007

### Teresa

going back to the death thing... if u went ova a blck holes event horizon, ur atoms would b ripped apart, as the gravitational difference between very small distances is so great... ie. the front of ur atoms would b travelling faster than the back of ur atoms and hence would b ripped to pieces... its not a nice way 2 die, but at least ud b going out with a bang =P