So at the CENTER of galaxies lie a supermassive black hole that eats other stars/black holes so they can grow even more bigger.

The diameter is only 44 million kilometers, almost a quarter of the distance from Earth to Sun, but the mass is 4 million Suns big!

The purpose of this topic is to discuss black holes,

-how it occurs when a star blows up
-why it keeps 'eating' light/mass near it
-why Mega Black holes become the center of galaxies
-can it be destroyed and
-what's INSIDE a black hole.
-also what to do if the LHC makes a black hole in northern Europe

1) There are criteria that determine whether a black hole would actually form. Generally if you stuff a lot of hydrogen together at some location, the gravitational force is counteracted by the fusion of the hydrogen nuclei. When this process stops eventually (it depends on what's the final products - it need not all be iron), you don't really have anything to counteract the gravitational force, and you end up getting a star collapse. They do not always end up turning into black holes though - it depends on the mass of the initial star, and its angular momentum. You may end up with dwarfs, neutron stars, or black holes

2) Gravity is an attractive force, and will attract mass. Light, although it has no mass, will also be 'pulled' by gravity [kinda lazy to explain technically why]

3) They tend to be the best candidate objects, but there probably exist galaxies where mega black holes are not the centre of, so no, that's not strictly true

4) You cannot destroy black holes, well at least from what we know now. They do evaporate over time though (I stress that this has not been observed, afaik, but there is strong evidence as to why this evaporation should occur), in a process called Hawking Radiation (which is one of the things that made Stephen Hawking so famous)

5) The black hole, as far as we know, is just a collection of mass, very dense mass. There's something called a no-hair theorem that states black holes have no hair (i.e. no personalities), and all black holes can be described using 3 observables, angular momentum, charge, and mass.

6) Depends. The black hole might have an extremely high momentum relative to Earth, and just gets shot out of the planet relatively quickly, and perhaps the Solar System in due time. If Hawking's prediction is right, then the black hole will evaporate in the LHC, and he'll probably end up with a Physics Nobel Prize. If however, Hawking is wrong, and the black hole stays in the LHC and continues accumulating mass [the black hole in the LHC, if created, will be extremely small, and have quite low gravitational attraction], we're all screwed!

It is quite probable though that it would be possible to eject the black hole out of the Solar System relatively quickly, but frankly the likelihood of a black hole being created and then swallowing us all is bloody bloody small.

This post has been edited by bgeh: Sep 7 2009, 10:15 AM

I can throw in my few cents on this. Every celestial object with gravity has an escape velocity associated with it. A particle needs a certain minimum velocity to escape from its gravitational pull. The escape velocity is a parameter independent of the particles mass, and depends only on the mass and radius of the object to be escaped from. In a black hole, the mass is so great and radius so low that the escape velocity is greater than the speed of light. More reading: http://en.wikipedia.org/wiki/Escape_velocity

EDIT: This is a simplified explanation from Newtonian physics. I'm not too sure about the concept in Einsteins relativity. Iinm it was basicly the curvature of spacetime collapsing at the singularity and light gets sucked in as well

This post has been edited by joe_star: Sep 7 2009, 08:36 AM

A popular analogy would be to imagine spacetime as a stretched fabric. If you place a mass on the fabric it would create a curvature. Objects travelling close to this mass would have their trajectories affected by this curvature (as it "rolls" across the fabric curvature). As it turns out light is affected in a similar way. Black holes can be conceptualized as points of infinite mass, which would result in a really "deep" dimple in the fabric. Objects falling into this fabric "trap" would then be unable to escape due to the steepness of the walls. The key point here is that the acceleration experienced by an object is an effect of the curvature of spacetime, and not as a product of a force of an object (which requires interactions between quantities with mass to exist in classical Newtonian physics)

In Newtonian physics, gravity describe as a force but in General Relativity gravity is no more the normal force we feel or experience but some kind of curvature of the spacetime cause by mass and energy(mass-energy equivalence from special relativity). So if there is a mass, then if some other mass smaller compare to it will roll to the center of the larger mass in a curve trajectory in global sense, but in local sense all the smaller mass experince is only a straight trajectory( this is where the 1st Newton's law!). It would be the case as in 4the post said if explain in terms of the fabric manners.
About the explanation of light is, light is some kind of energy with no mass, so it would also be drag by the larger mass source as ordinary particle. From this we can expain about the bending of light at gravitational sources(like our sun). When the gravitational source is too large(like black hole), the time required for light escape from it is larger and larger and even became infinity in the event horizon, so the time as if freezed near the event horizon and we know nothing from black hole because the light signal can never reach us.( Not quite sure about the explanation at this paragraph in more precise and technical sense but almost the case as we know today).
Before we have the Hawking radiation theory, we just expect that we can never reach to the information stored inside a black hole, but after it, we expect to get some information form the Hawking radiation. ( almost i can tell... the rest i also quite understand) Intersted people can go read black hole thermodynamics and about some quantum information theory.

Imagine a gateway of higher dimension, which connect the lower dimension (our visible 3 dimension); except that it also connect to multiple 3 dimension. Blackhole is a 3 dimensional hole. Like a sphere, but instead of solid, it's a hole.

The deduction that the center of universe is a blackhole, is simply the could display such enormous mass.

black hole is like a mouth

it sucks in everything

and at the other end (not yr normal 3D thingy) it spouted out stuffs, like the anus

in creating new universe in new dimension

never forget that when our universe was first formed, it had more than 45 dimensions, now we can detect 4 of it and can theorize 3 others, for a total of 7

45 dimensions? M-theory can reduce the dimensions to only 12 and only 12 is fit the thoery. For lqg we don't even look at extra dimesions but we foliate the spacetime into space and we take no more time but the evolution of the spin network(which is space) and this evolution of network forms our ordinary 4 dimesion view of spacetime - spinfoam.
Anyway, this thread is talking about the macro physics, so no need of quantum theory and quantum gravity to discuss, just general relativity.
btw, the white hole that convivencia is still a conjecture, not even a theory and thus proven yet. in the theory, star collapse to black hole and "sucks" everything around it, emits Hawking radiation and other kind of radiation plus heat, while white hole doing the opposite thing, "spouts" out everything the black hole sucks, create a new star or galaxy or even universe and this two "hole" connected by wormhole.

This post has been edited by nobunaga84: Sep 17 2009, 09:12 PM

Hahahaha what the f***.

How about, this?

http://en.wikipedia.org/wiki/Event_horizon

Answer to question number two.

My oh my.. This discussion is really.... OUT OF THIS WORLD!! XD

Am reading every posts, really enlightening! Now this is what i'd call a nice discussion XD

2) I'm interested to know how it works. But i'm not well learned in astrology. Will i be able to understand it?

6) wat's LHC?

45 dimensions!? But.. Like... How...?
oh my... My mind can't process all these information... @@

Dearie you need to learn to use Google.



http://en.wikipedia.org/wiki/Large_Hadron_Collider

1st of all, in science, this is called astrophysics, not astrology. astrology is more to the horoscope prediction etc... that's still not a branch of science. for the science of observation on the stars etc, that's astronomy, for the science to learn about the birth of universe etc or in precise word learn the universe as a whole, that's called cosmology. each of this still have their branches, like quantum cosmology etc.

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Added on October 5, 2009, 1:08 pmabout the extra dimensions, u can read string theory. string theory as one of the popular approach to the quantum gravity require extra dimension to support its consistency. in supergravity we need 13(if i'm not mistaken) dimension in total, in M theory we need 11 dimensions, in brane localized gravity we need 5 dimensions. in the theory of extra dimensions, all the extra dimensions out of our ordinary 4 dimensions is compactified(e.g. like Calabi-Yau manifolds).

anyway, in another popular approach to quantum gravity, loop quantum gravity we doesn't require extra dimension.

This post has been edited by nobunaga84: Oct 5 2009, 01:10 PM

-how it occurs when a star blows up
when a star explodes, it will expand at unimaginable rate to mind blowing sizes.... and when it reach max point, it`ll bounce back... take a spring for example... when u toss it, it will elongate till a point and it`ll bouce back... at that point, the star contracts at the same rate it expand to very dense "rock" some rock turn out to be white dwaf; some become dead star; some become black hole...


-why it keeps 'eating' light/mass near itnk you should
i think you should read on space continumn on this.. i recommend stephen hawking`s brief history of time and the universe in nutshell
once you read it, you`ll understand everything


-why Mega Black holes become the center of galaxies
first and foremost, in galaxy, thereare no center... everything is the center of each other....

-can it be destroyed and
no one knows

-what's INSIDE a black hole.
still debating by the scientist... but theoretically, it is said a "white hole" that "vomit" everything out could be connected with black hole and form worm hole.. this worm hole could be used as teleportation and time travel


-also what to do if the LHC makes a black hole in northern Europe
only god knows why... bon jovi

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Added on October 5, 2009, 1:23 pmi think space time continumn is best to explain that question.. event horizon is just a point of no return

This post has been edited by Awakened_Angel: Oct 5 2009, 01:23 PM

ooops. my bad ><
I've alot of questions in my mind, can't phrase it out..
Perhaps it'd help if i do some reading on my own first.
Thanks

no.. you don`t have to read.. I bought the book.. i read it half way and discover the "movie" version of string theory with teh same author in the documentary explaning in words

you can watch it in you tube

http://www.youtube.com/watch?v=E7FV9aaiwKQ

got few parts
ever since as a child, I was facinated by the vastness and mystery of deep space...

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Added on October 5, 2009, 4:30 pm

ever since einstein proposed possibility of time travel, the entertainment sector used this point for their so called "blue ocean"


This post has been edited by Awakened_Angel: Oct 5 2009, 04:30 PM

Oh. Thanks XD
I'm gonna load the youtube vid now. thanks alot!

I was just as fascinated. However as i grew older, with parents and realistic factors coming in (such as the prospect of studying about space), made me not wanting to go any further in. :/

But oh well, it still stirs up my mind of how much of things we have yet to know/discover/understand. That feeling, is just so awesome.. XD

agreed

I was scold the hell out of my parents when I say I wana study astrophysic for my Uni...

at night.. seeing the deep sky with thing that I read from book playing in my mind is just awesome

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Added on October 5, 2009, 9:09 pmi come across this few documentary... I loved it.. just for sharing

every topic in astrophysic is linked with each other.. once u understand one.. you understand the other

http://www.tom365.com/movie_2004/html/7152.html]http://www.tom365.com/movie_2004/html/7152.html

http://www.tom365.com/movie_2004/html/6942.html

http://www.tom365.com/movie_2004/html/6951.html

cheers

This post has been edited by Awakened_Angel: Oct 5 2009, 09:11 PM

Schwarzchild Radiussssss........

IIRC there is a distinction between Black holes and a worm holes, the former having no end and the latter having an exit.

The reason why they're black? Well, simply they bend spacetime itself, all gravity bends space and once space becomes infinitely deep and the curvature of space itself is also infinite once you get to the singularity in the middle.

Blahblahblah, i'm just happy, i went shooting and shot alot of shit. Yeehawww.

that radius is the radius of event horizon....

there was this simple explanation... density=mass/volume....

when star contract after big bang, it contract to the rate reaching 0 but never will hit zero... so, let us assume the rate as 0

therefore, density=mass(which is star mass)/0= infinity....

when a star is said to hit infinite density, i`ll form a gravitational well so steep that not even light can escape, and the boundary of non return is called event horizon.. and put in number, called Schwarzchild Radiussssss........