I keep having dreams about black holes, they are fascinating to me but since I'm an idiot, I'm not sure I understand them.

I get that they are not "holes" per se, but regions that absorb matter and energy.  But what does that mean -- how does a region absorb anything? 

Also, I get that they can grow but do they just keep growing?  Is there an end state for a black hole? If they just keep growing and growing, wouldn't the universe eventually become one giant black hole, or a least a region of black holes surrounded by empty space (presumably with the black holes being far enough away from each other so as not to collide, etc).

What gives with these fuckers?

https://en.wikipedia.org/wiki/Schwarzschild_radius

https://en.wikipedia.org/wiki/Schwarzschild_radius

This is a good description, but it only describes what a black hole is in theory (and it's not the best description I've seen.....

Ty, you understand the concept of escape velocity? It's simply how fast something needs to be going to escape the gravitational pull of a large mass, like a planet or star.  The escape velocity of earth is about 11 km/s. Once something gets big and dense enough that the escape velocity is equal to or greater than the speed of light, it becomes a black hole The math isn't terribly difficult as a first approximation, but it's also not really that important.

Now, Black holes only 'grow' when they suck in more matter, because it adds to the effective mass of the black hole. However, it's not just a simple matter of matter falling into a black hole like an object falling to earth. Because of the tremendous forces involved, matter gets accelerated, heated, and generally fucked about such that only a portion of the matter approaching the black hole actually 'goes in'. Much of it is turned to high energy plasma and goes jetting off into space. (This is how we can actually see most black holes).

And black holes in the absence of immediate matter to 'feed' on hypothetically can 'evaporate' (for lack of a better term) via Hawking radiation. And keep in mind, the only reason black holes are 'scary/ is because they are so small, relatively speaking. Their gravity isn't special, compared to a really large star (which is what most of them started as)....it's still just gravity.

Their gravity isn't special, compared to a really large star (which is what most of them started as)....it's still just gravity.

Oh, just you wait until we find naked singularities.

 matter -->     <-- gravity

HTH

Don't tell him about the inflationary multiverse hypothesis. 

https://en.wikipedia.org/wiki/Schwarzschild_radius

This is a good description, but it only describes what a black hole is in theory (and it's not the best description I've seen.....

Ty, you understand the concept of escape velocity? It's simply how fast something needs to be going to escape the gravitational pull of a large mass, like a planet or star.  The escape velocity of earth is about 11 km/s. Once something gets big and dense enough that the escape velocity is equal to or greater than the speed of light, it becomes a black hole The math isn't terribly difficult as a first approximation, but it's also not really that important.

Now, Black holes only 'grow' when they suck in more matter, because it adds to the effective mass of the black hole. However, it's not just a simple matter of matter falling into a black hole like an object falling to earth. Because of the tremendous forces involved, matter gets accelerated, heated, and generally fucked about such that only a portion of the matter approaching the black hole actually 'goes in'. Much of it is turned to high energy plasma and goes jetting off into space. (This is how we can actually see most black holes).

And black holes in the absence of immediate matter to 'feed' on hypothetically can 'evaporate' (for lack of a better term) via Hawking radiation. And keep in mind, the only reason black holes are 'scary/ is because they are so small, relatively speaking. Their gravity isn't special, compared to a really large star (which is what most of them started as)....it's still just gravity.

Thanks for that.

Would it be accurate to say that black holes are actually bodies, and not regions?

Also, given the nature of the black hole's propensity to just grow and grow, will the universe eventually just be black holes that haven't collided with each other (yet) or would heat death occur before black holes can absorb everything?

Would it be accurate to say that black holes are actually bodies, and not regions?

Also, given the nature of the black hole's propensity to just grow and grow, will the universe eventually just be black holes that haven't collided with each other (yet) or would heat death occur before black holes can absorb everything?

The appearance of a collapsed star (the singularity) is black because gravity is so strong even light is bent so hard it can't be viewed anymore.  It's not a hole, that's just a description.  It's a very strong gravity region, because a large star is compressed down to the size of slightly larger than an atom. (theoretical, nobody actually knows the size)

The region where light can not escape is considered the size of the "hole".

And yes, eventually the entire Universe will be black holes, but even they emit radiation (Hawking radiation) so they will eventually disappear as well, leaving a cold nothing for all eternity.  (theoretical)

This will happen a very long time after everybody is dead, so don't worry too much about it.

And before anyone says the size is zero (general relativity theory) just remember you don't actually know.  Nobody does.

Where nothing can be observed is called the event horizon, which is not the same as zero.  The event horizon is not the same as the singularity.

Would it be accurate to say that black holes are actually bodies, and not regions?

Also, given the nature of the black hole's propensity to just grow and grow, will the universe eventually just be black holes that haven't collided with each other (yet) or would heat death occur before black holes can absorb everything?

The appearance of a collapsed star (the singularity) is black because gravity is so strong even light is bent so hard it can't be viewed anymore.  It's not a hole, that's just a description.  It's a very strong gravity region, because a large star is compressed down to the size of slightly larger than an atom. (theoretical, nobody actually knows the size)

The region where light can not escape is considered the size of the "hole".

And yes, eventually the entire Universe will be black holes, but even they emit radiation (Hawking radiation) so they will eventually disappear as well, leaving a cold nothing for all eternity.  (theoretical)

This will happen a very long time after everybody is dead, so don't worry too much about it.

Cool.  But to press further, there is an object in there somewhere, right?  It sounds like "Black Hole" describes a collection of things: an object of incredible density, surrounded by a region from which nothing can escape because of gravity. Is this correct?

Also, if a black hole presents a region so strong that nothing can escape, how can anything radiate from it, or how can plasma jet from it? 

Also, if a black hole presents a region so strong that nothing can escape, how can anything radiate from it, or how can plasma jet from it? 

https://en.wikipedia.org/wiki/Hawking_radiation

The plasma/jets are are outside the event horizon.

https://en.wikipedia.org/wiki/Astrophysical_jet

But to press further, there is an object in there somewhere, right?  It sounds like "Black Hole" describes a collection of things: an object of incredible density, surrounded by a region from which nothing can escape because of gravity. Is this correct?

Pretty much.

There is matter in there.  It's just so small it's considered zero size.  No seriously, it is considered that.  And then there is the event horizon.  Two different "things", but with the same cause. 

Interesting, thank you.

Cool.  But to press further, there is an object in there somewhere, right?  It sounds like "Black Hole" describes a collection of things: an object of incredible density, surrounded by a region from which nothing can escape because of gravity. Is this correct?

There certainly is mass in it, so I guess that makes it an "object". But the nature of the mass at that density is something that would be completely unfamiliar to ... well, to me anyway.

Is there a good book on all of this I can read, that is not too over-the-top?

ETA:  I realize I can go an amazon and look but with that review system nowadays . . . ehhh . . . I dunno . . .

It's pretty cool that Subrahmanyan Chandrasekhar came up with the concept while on a ship to London from India.  Seriously, on a deck chair on a ship.  With just his mind and a pencil and paper.  And of course the theory of general relativity.

Is there a good book on all of this I can read, that is not too over-the-top?

E=mc2 is a fun and very interesting book, that covers black holes as well as almost everything else involving E=mc2

https://www.amazon.com/mc2-Biography-Worlds-Famous-Equation/dp/0425181642

Is there a good book on all of this I can read, that is not too over-the-top?

E=mc2 is a fun and very interesting book, that covers black holes as well as almost everything else involving E=mc2

https://www.amazon.com/mc2-Biography-Worlds-Famous-Equation/dp/0425181642

Just bought the Audible version.  Thanks!

You are welcome!  My copy is falling apart, I have read it a dozen times.  I hope you enjoy it.

Would it be accurate to say that black holes are actually bodies, and not regions?

Also, given the nature of the black hole's propensity to just grow and grow, will the universe eventually just be black holes that haven't collided with each other (yet) or would heat death occur before black holes can absorb everything?

The appearance of a collapsed star (the singularity) is black because gravity is so strong even light is bent so hard it can't be viewed anymore.  It's not a hole, that's just a description.  It's a very strong gravity region, because a large star is compressed down to the size of slightly larger than an atom. (theoretical, nobody actually knows the size)

The region where light can not escape is considered the size of the "hole".

And yes, eventually the entire Universe will be black holes, but even they emit radiation (Hawking radiation) so they will eventually disappear as well, leaving a cold nothing for all eternity.  (theoretical)

This will happen a very long time after everybody is dead, so don't worry too much about it.

Cool.  But to press further, there is an object in there somewhere, right?  It sounds like "Black Hole" describes a collection of things: an object of incredible density, surrounded by a region from which nothing can escape because of gravity. Is this correct?

Actually, to get all philosophical on you, we define objects by their boundaries. River, current, eddy, those are all nouns. I would say that the region inside of the event horizon is an object as much as anything is. Is a breath a part of your body? Borders are always permeable. Even, according to Hawking anyway, the borders of a black hole.

You are welcome!  My copy is falling apart, I have read it a dozen times.  I hope you enjoy it.

Most of my "reading" is now done via audiobook, at least leisure reading.  I spend about 2.5 hours a day commuting, but I can't read in a moving vehicle (train, plane, bus, you name it).  I get immediately sick.  So I have to listen to everything.  The problem with that is, a lot of narrators are pretty good and put me right to sleep, and I end up missing half the book.

The problem with that is, a lot of narrators are pretty good and put me right to sleep, and I end up missing half the book.

You just need to choose the correct type of narrator to keep you alert.

https://www.youtube.com/watch?v=XkLqAlIETkA

You are welcome!  My copy is falling apart, I have read it a dozen times.  I hope you enjoy it.

Most of my "reading" is now done via audiobook, at least leisure reading.  I spend about 2.5 hours a day commuting, but I can't read in a moving vehicle (train, plane, bus, you name it).  I get immediately sick.  So I have to listen to everything.  The problem with that is, a lot of narrators are pretty good and put me right to sleep, and I end up missing half the book.

Sup fellow motion sickie?