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_DRAGONLORD_
2006-Mar-12, 11:18 PM
Are they invisible:confused:

Dragon Star
2006-Mar-13, 12:33 AM
As far as light goes yes, they are because the black hole is so powerful light can not escape it.

antoniseb
2006-Mar-13, 01:44 AM
Black Holes: Are they invisible
It depend on what you mean by invisible. You can see where they are, and even if a black hole has no matter falling into it, it does give off gamma rays from Hawking radiation. Also, if you were moving relatively close to it, you'd notice some odd effects with the star seen behind it. If matter was falling into it, it would be pretty obvious to any nearby observer who could survive the radiation.

Kaptain K
2006-Mar-13, 07:59 AM
Although a black hole does not radiate and therefore is technically "invisible", it does not mean that we can not "see" where it is. If it has an accretion disk, the disk will radiate in all bands of the EM spectrum. Even if it does not have an accretion disk, we can still see where it is because the extreme gravity well distorts the background star fields.