...i love astronomy eversincce and as I get to know it better my fondness of it grows bigger....

.. there is an  something I wanna know about because it might change the course of the earth...

..can anyone explain to me what a blackhole really is? .. how are they formed?... and what it is made of?,........

thnx... hope u can answer my question... 

A black hole is formed when a star that is more than about 5 times the mass of our Sun, but less than about 10 times the mass of our Sun, collapses at the end of its "life."

Once a star begins to fuse heavier and heavier elements, it begins to run out of each element as fuel more rapidly than the previous element. That is, as it progresses through creating the heavier elements, it will reach a point where it begins to create iron. At that point, it begins to consume more energy than it releases and the star rapidly collapses. The catastrophic collapse happens in less than a second or two and the remaining stellar mass is crushed under such gravitational pressure than the matter in the star's core becomes sealed off from the rest of the universe.

The gravitational curvature of spacetime is so steep a gradient that not even light can escape from "inside" the star. Hence, it no longer radiates and is "black" (invisible).

That's it, in a nutshell.

So, it's made from the usual star stuff, but once it's collapsed we have no way of telling what state the matter is in (since we can't see or measure it).

I've read various theories on what a black hole consist of. Stephen Hawking I believe theorizes that a black hole is not completely black. Theories on other subjects related to what a black hole consists of. Some say that the star matter that collapsed into a black hole becomes non-existent, all that's left is the intense gravitational tug of the former infinite mass. (Don't ask me how this occurs, I have no idea as I am just relaying theories.) I've also read a number of books on the subject, one which states that a black hole is merely a rip in the space-time of the universe. When matter enters the black hole it falls through and becomes non existent in our reality.

...but is true that black holes have this great gravitational pull that they attract things toward them...like they swallow things that go near them?

 Yeah, juvenilealchemist, that's true.  They have a very strong gravitational pull, and that's generally how we're able to detect them - by analyzing the movements of stars, say, in the middle of a galaxy.  Chances are, if they're moving very quickly in an orbital fashion, they're interacting with a black hole before they're swallowed up entirely. 

At least, that's what I know from my dabbling in such information.  I'm sure it's far more complex and full of wonderful formulas this brain can't comprehend.

 They're wonderful things, and there is a plethora of theories attached to them.  I was just watching an odd program yesterday that claimed there might be a black hole in the earth sucking up ships in the Bermuda triangle.  (Totally bogus, but, still, they attract a lot of attention for their strange qualities.)
 

...how threatening are they?...and can you please explain to me the theory about the  doomsday?...the planet X thing...it sounds so interesting and at the same time frightening...thank you!!

 

The gravitational pull of a black hole is so strong that it pulls in everything, including light. After that it just disappears, torn apart by the sheer force of the gravity in the hole...

 

One theory is that it is a collapsed star, one that was simply too big for its own good, and its own gravitational pull made it collapse in on itself...

...so its not visible?...can it possibly pull a mass as heavy as Saturn's?...

.....self-destructs?....what are it's contents?....are their numerous black holes scattered out there in space?

juvenilealchemist:

...so its not visible?...can it possibly pull a mass as heavy as Saturn's?...

Don't panic, and forget about that Planet X hysteria.

As I've described above, and many places elsewhere here in the forum, the current model for forming a black hole is the collapse of a massive star. The star must be at least a few times more massive than our Sun, and be less massive than would be required to blow the star apart in a supernova. Estimates for the proper mass vary, but generally a star more than about 3, and less than about 10, solar masses would do it.

When such a star quits fusing lighter elements and starts fusing carbon, it hasn't long to live. Practically the instant it begins to fuse iron it ceases to produce energy from fusion and begins to consume energy in that reaction. This rapidly leads to the star's collapse, which happens so suddenly that the star's core shrinks past neutron rebound (it happens too quickly for that to occur) and forms the black hole.

Note that it's only the star's core that initially forms the BH. Therefore, the resulting BH is actually less massive than the original star. That means its gravity is also less. But that gravity is acting over a very much reduced radius. This, in turn, means that the BH's gravity curves spacetime so greatly that no matter within a very short distance of the event horizon (nearer the BH than the original star's radius) can escape.

Note, also, that this does NOT mean that objects that were originally in orbit around the star are in any immediate danger of "being sucked in" ... the BH is not some cosmic vacuum cleaner that attracts everything to it.

From the standpoint of possibly pulling a mass as great as Saturn, the proper way to think about it is that if our Sun were massive enough to form a BH, it would not have much effect on Saturn, since Saturn is so far from its event horizon. If you were in orbit about Saturn when the BH formed, you would experience very little change in your orbit at the instant the BH formed, and for some time afterward. Saturn would not automatically "fall into" the BH.

A thorough yet readable account of current models for Black Holes is Kip Thorne's Black Holes & Time Warps, Einstein's Outrageous Legacy, which I highly recommend.

juvenilealchemist:

.....self-destructs?....

Not exactly. Hawking's model is that black holes can radiate in a kind of leakage ... but his calculations show that the typical black hole wouldn't dissipate into nothingness in less than dozens of billions of years.

what are it's contents?....

There is no way to be sure. The original star's core has to go "somewhere" (inside the black hole). Some conjecture that it goes into alternative dimensions, but if it does then somehow it remains gravitationally connected to our own universe.

are their numerous black holes scattered out there in space?

Yes. Observations of the orbits of stars near the core of the Milky Way lead us to believe there is at least one supermassive black hole there. Observations of the motions of stars in globular clusters lead us to believe there may be black holes in some of them. Observations of the energy output from distant quasars lead us to believe that perhaps a high percentage of them are what are called Active Galactic Nuclei -- one model for which is supermassive black holes which are "feeding" on stars, gas, and dust at the core of a galaxy.

Another form of "micro" black hole may have been formed by the Big Bang. There could be trillions of these, according to some models. Whether they could grow at all, or were only present for small periods, is at present only conjecture. They are not observed.

As has been pointed out in other replies here, we observe black holes by their effects on matter which is near them (near enough that orbits are affected, for example). Matter which orbits a black hole very near (but outside) its event horizon accelerates and glows due to friction, so we can see the event horizon in such a case, but not the black hole itself (once matter crosses the event horizon it disappears from view, because light cannot escape from beyond the event horizon).

...so its not that dangerous as it seem to be at all?.......thank you so much for the very knowledgeable explanation...hope to have a discussion with you more often...take care!!

...wow there are really a lot of things that can be discussed about the black holes...its a really interesting subject.....somebody told me here in the forum about the Bermuda triangle and that the there is a theory that the culprit behind the mysterious things that is happening in that area is a black hole do you believe that idea?.....and about the doomsday thing  is it just a hoax or is it a proven science fact?

juvenilealchemist:

...somebody told me here in the forum about the Bermuda triangle and that the there is a theory that the culprit behind the mysterious things that is happening in that area is a black hole do you believe that idea?

No, there is no evidence that this sort of thing is possible. It's not even science fiction (just the plain old garden variety).

.....and about the doomsday thing  is it just a hoax or is it a proven science fact?

No, it is not proven scientific fact. It is at best speculation, if you're referring to this existence of Planet X. If you're referring to the prediction that 2012 marks the end of the world as doomsday, then it's not even crank science ...

There are way too many other threads here in the Forum about 2012, Nibiru, and Planet X ... we don't need yet another one.

....thank you for the informations......so there's  nothing to worry about........back to black holes what is the essence of there existence?

Im not sure what you mean by essence? As already mentioned its a region of space in which the gravitational field is so strong that nothing can escape. It is called a black hole because not even light can escape. According to general relativity, a black hole's mass is zero volume, which means its density and gravitational pull are infinite.

 yeah, it can pull anything into it... so hopefully there aren't any stars too close that are ABSOLUTELY huge and collapse on themselves...

there's also a  white hole, which is the opposite of a black hole and spews out everything, don't ask how this is formed, i don't know ( i'm only fourteen) the white hole even spews out light, and scientists have theorised that if a black hole and a white hole joined it might be the key to time travel...

 I've not heard of a White hole. Could anybody find a link to info?

And Black holes don't suck. They pull/push. 

...i mean what is its role in the universe...is it just to pull things?...does it have an important role to play?