some questions on black holes

[tali122]

if a star dies to create a black hole - does a black hole die ? - if so what becomes of it?
are all black holes like a whirlpool /trumpet/tornado shape that taper off at the bottom to a pin head size- or are some black holes actually the size of pin heads? what happens when black holes closely pass each other?
can someone analagize or quantify the density of a black hole?
if it were possible would a black hole allow you to see back in time as in relativeity theory?
thanks

[Clanad]

Let's start at the last part of your question first, if I may... actually, anytime you look at a star,our Sun or even the moon, you are, in a very real sense, looking back in time. The light from the sun, for example takes, on average 8 minutes to reach earth. So, you are actually seeing something that happened 8 minutes ago. Same principle applies to the theoretical looking into a black hole.

Before any meaningful discussion can take place about the theorized phenomena, we have to understand that facts and figures about black holes and their behavior are few and far between. Due to their nature, no one has actually ever seen one. I know, I know, there are photographs of x-rays escaping from what are probably black holes, but by their very nature, they can't bee seen. My understanding is that the smallest theorized black hole is about 8 miles across. This includes the accretion disk and event horizon. A hypothesis that is developing talks about minature black holes, the size of just several billions of tons, but it is highly suspect for now, whereas massive black holes are believed to be several billion solar masses in size. In each, however, the singularity, the center of the hole where nothing, not even light (exception x-rays) can escape are infinitely small but infinitely dense.

By the way, black holes can be spinning ones or stationary ones, according to current theory.

The quantum physics involved in predicting, identifying and quantifying black holes is so esoteric, that most scientists involved spend their entire professional lives devoted to its singularity (pun only slightly intended).

Lastly, as references your question (which I haven't answered very well) understand that not all dying stars become black holes, thankfully. Else we wouldn't be here to talk about it.

[bernardo]

There is a theory that black holes evaporate by giving off Hawking radiation. This happens when a thingy spontaneously appears just outside the edge of the black hole, and splits into two sub-thingies. Normally the two sub-thingies re-combine and disappear again, but if it is close to the edge of a black hole then it is possible for one sub-thingy to fall in and disappear, leaving the other sub-thingy to escape. This provides a mechanism whereby energy can appear to be removed from the black hole so that it eventually disappears.

The whirlpool-type shape that they show in computer animations is not the real shape of a black hole; it is sort-of spherical. The whirlpool-shape is the 3-dimensional representation of a distorted 2-dimensional space; it is a simplified version of what a black hole would look like if we could see it from 4-dimensions. The 3-dimensioanl space in which we live is distorted by gravity into a 4th dimension.

[einsteinsdog]

It might be worth saying that the very nearest black holes are still millions of millions of miles away. To get it all in perspective.

[einsteinsdog]

How about black holes losing energy by radiating gravity waves as predicted by er hum

[boobesque]

gravity waves?

can i point out that in hawking radiation, the 'virtual particles' are a positive and negative particle anti-particle pair. virtual particles are created from nothing. take 0 and minus a positive 1. you are left with a positive and a negative 1. if one half gets pulled in to the black hole and the other escapes then nothing is evaporating. assuming that on average, an equal amount of + and - virtual particles are pulled in then they will nullify each other but the rest of the black holes mass will remain unaffected.