# Thread: space regarding collapsing stars...

1. before a star dies/collapses it becomes a red giant, meaning it's x times bigger. then after it collapsed it's x times smaller with the same energy? i.e. black hole?

2.

3. It depends on the mass of the star. You have a question mark- but the question is unclear.

4. Also a lot of mass is blown away when the supernovae explodes. (That is what we are made of!)

5. so not every star that dies becomes a red giant first, or your reply applied to the black hole? ... if so, what happens then?

6. a lot of mass that only = a fraction of the star?

7. Originally Posted by curious mind
so not every star that dies becomes a red giant first, or your reply applied to the black hole? ... if so, what happens then?
No. A star the size of our sun will become a red giant, stay that way for a few million years or so and then shrink to a dwarf. Stars larger than the sun will end in supernova, and if the star was large enough so that sufficient matter remained after the outer layers are blown off, it will become a black hole.

8. This is what happen:
1) a normal star create fusion,
2) this fusion create byproduct such as helium & also keep the star inflated,
3) the star became fatter because of the byproducts,
4) the star collapse due to its own gravitational pull (getting dense, depleted fusion reaction!),
5) fat stuff get compressed down to quantum level,
6) heinsenberg principle state that: anything compressed to more defined space will have higher random speed,
7) sudden random speed occur! (quantum pressure emerge!),
8) star explode crazily! (SUPERNOVA),
9) excess fat is lost (iron, uranium, and all fat stuff is lost into deep space),
10) remaining matter became tightly dense object: either became a neutron ball (still tightly packed to quantum tiny space) or a black hole (undefined packing space!!)

Interesting stuff is this quantum pressure. It cause explosion rivalling fusion power.

9. Originally Posted by msafwan
I think this is what happen:
1) a star create fusion,
2) this fusion create byproduct such as helium,
3) the star became fatter because of this byproduct,
4)the star collapse due to gravitational pull,
5) fat stuff get compressed down to quantum level,
6)heinsenberg principle state that: anything will more defined space (stuff which compressed to 1 location) has higher random speed,
7)sudden random speed occur! (quantum pressure!),
8) star explode crazily!,
9) excess fat is lost (iron, uranium, and all fat stuff is lost!),
10) left out matter became tightly dense object: either a neutron ball (still tightly packed to quantum tiny space) or a black hole (undefined packing space!!)
Well... You started out doing pretty well...

10. Originally Posted by msafwan
This is what happen:
1) a normal star create fusion,
2) this fusion create byproduct such as helium & also keep the star inflated,
3) the star became fatter because of the byproducts,
4) the star collapse due to its own gravitational pull (getting dense, depleted fusion reaction!),
5) fat stuff get compressed down to quantum level,
6) heinsenberg principle state that: anything compressed to more defined space will have higher random speed,
7) sudden random speed occur! (quantum pressure emerge!),
8) star explode crazily! (SUPERNOVA),
9) excess fat is lost (iron, uranium, and all fat stuff is lost into deep space),
10) remaining matter became tightly dense object: either became a neutron ball (still tightly packed to quantum tiny space) or a black hole (undefined packing space!!)

Interesting stuff is this quantum pressure. It cause explosion rivaling fusion power.
Degenerate matter is a very interesting topic. Personally I believe deeper levels of degeneracy take place on the other side of a BH event horizon. But that's pure speculation on my part and will probably remain unprovable for many years to come.

Degenerate matter

Degenerate matter in physics is a collection of free, non-interacting particles with a pressure and other physical characteristics determined by quantum mechanical effects. It is the counterpart of an ideal gas in classical mechanics. The degenerate state of matter (in the sense of deviant from an ideal gas) arises at extraordinarily high density (in compact stars) or at extremely low temperatures (in the lab). It occurs for matter particles such as electrons, neutrons, protons, and fermions in general and is referred to as electron-degenerate matter, neutron-degenerate matter, etc. In a mixture of particles, such as ions and electrons in white dwarfs or metals, the electrons may be degenerate, while the ions are not.

Degenerate matter - Wikipedia, the free encyclopedia

11. Originally Posted by msafwan
This is what happen:
1) a normal star create fusion,
2) this fusion create byproduct such as helium & also keep the star inflated,
3) the star became fatter because of the byproducts,
4) the star collapse due to its own gravitational pull (getting dense, depleted fusion reaction!),
5) fat stuff get compressed down to quantum level,
6) heinsenberg principle state that: anything compressed to more defined space will have higher random speed,
7) sudden random speed occur! (quantum pressure emerge!),
8) star explode crazily! (SUPERNOVA),
9) excess fat is lost (iron, uranium, and all fat stuff is lost into deep space),
10) remaining matter became tightly dense object: either became a neutron ball (still tightly packed to quantum tiny space) or a black hole (undefined packing space!!)

Interesting stuff is this quantum pressure. It cause explosion rivalling fusion power.
haha that is not correct

12. ok thanks, i just needed clarification regarding the space. but it also shows that black holes are a closed system as hawkins stated.

13. Degenerate matter is a very interesting topic. Personally I believe deeper levels of degeneracy take place on the other side of a BH event horizon. But that's pure speculation on my part and will probably remain unprovable for many years to come.
Interesting, I have a very similar understanding. To me a "black hole" is simply the highest form of degeneracy; what exactly that form is will depend on the fundamental nature of matter. Once such possibility would be Samir Mathur's "Fuzzball" model, which resolves many problems quite beautifully. Truth is, however, that at this point in time we simply don't know yet.

14. maybe i misinterpreted the meaning of a closed system. but either way, wouldn't you end up with more space regarding the compressed one?

15. Originally Posted by curious mind
but it also shows that black holes are a closed system as hawkins stated.
I doubt that he did state that, given that he proposed the existence of Hawking Radiation.
Plus the FACT that Black Holes take in matter from around them is a certain indicator that they aren't "closed systems".

16. Originally Posted by curious mind
maybe i misinterpreted the meaning of a closed system. but either way, wouldn't you end up with more space regarding the compressed one?
I'm not sure what that means. Note that the radius of a black hole is proportional to its mass:

17. Surely he doesn't mean that since the compressed star is taking up less space there must now be more space available?

18. Originally Posted by John Galt
Surely he doesn't mean that since the compressed star is taking up less space there must now be more space available?
yes, that's what i meant.

19. In which case the answer is "no".
There'd be more room, but exactly the same amount of space.
Matter occupies space - it doesn't displace it.

20. Originally Posted by Dywyddyr
In which case the answer is "no".
There'd be more room, but exactly the same amount of space.
Matter occupies space - it doesn't displace it.
ya well room has the same meaning as space to me. if you have a football and compress it to the size of a pea, you're left with more room/space.

so when a star becomes a black hole, even considering the amount of mass that gets blasted into space, proportional you'll have an area with a smaller radius (more room) but with the same density on average still.

21. Originally Posted by curious mind
ya well room has the same meaning as space to me.
Well that explains one error, at least.

22. so my comment in #19 isn't correct?

23. Originally Posted by curious mind
so when a star becomes a black hole, even considering the amount of mass that gets blasted into space, proportional you'll have an area with a smaller radius (more room) but with the same density on average still.
The radius of a black hole will be much smaller than the equivalent mass star. For example, the radius of a black hole with the same mass as the sun would be about 30km (while the radius of the sun is about 700,000km).

The density of a black hole isn't really a meaningful measure. But the radius is proportional to mass, therefore the volume is proportional to mass3, therefore the average density is inversely proportional to the mass2.

The average density of a solar mass black hole would be billions of times greater than the sun. But a supermassive black hole could have an average density similar to water (which is about the average density of our sun, I think).

24. Originally Posted by curious mind
so my comment in #19 isn't correct?
Your comment #19 was clarified in my post #18.

25. Originally Posted by Strange
The average density of a solar mass black hole would be billions of times greater than the sun. But a supermassive black hole could have an average density similar to water (which is about the average density of our sun, I think).
I don't understand. Why is supermassive black hole has average density of water? Does this mean a sphere of water make a black hole? I don't get it, what is this average density everyone talking about???

26. Originally Posted by msafwan
I don't understand. Why is supermassive black hole has average density of water?
Because a black hole event horizon has a radius (Schwarzschild radius) which is proportional to its mass: .

From that you can calculate a volume (which will be proportional to mass cubed). But this is rather meaningless as the inside of the black hole is no longer part of our space-time and it isn't clear (to me) whether the concept of volume inside the event horizon makes any sense - what with time and spatial dimensions getting swapped and all).

From that you can calculate a value called "density" which is proportional to mass / mass3; i.e. proportional to . But again, this is pretty meaningless. Our current best theory says that everything gets crushed to infinite density at the center.

Does this mean a sphere of water make a black hole?
Yes, if you had a drop of water with the mass of 100,000,000 suns then it would collapse under its own weight and form a black hole.

27. Originally Posted by Strange
Originally Posted by curious mind
so when a star becomes a black hole, even considering the amount of mass that gets blasted into space, proportional you'll have an area with a smaller radius (more room) but with the same density on average still.
The radius of a black hole will be much smaller than the equivalent mass star. For example, the radius of a black hole with the same mass as the sun would be about 30km (while the radius of the sun is about 700,000km).

The density of a black hole isn't really a meaningful measure. But the radius is proportional to mass, therefore the volume is proportional to mass3, therefore the average density is inversely proportional to the mass2.

The average density of a solar mass black hole would be billions of times greater than the sun. But a supermassive black hole could have an average density similar to water (which is about the average density of our sun, I think).

i meant the the whole area, not only the area where the star has been. even though the density, where you now have the black hole, is higher with a smaller radius; than what the sun had before. the overall density of the whole area would still be the same.

28. Originally Posted by curious mind
i meant the the whole area, not only the area where the star has been. even though the density, where you now have the black hole, is higher with a smaller radius; than what the sun had before. the overall density of the whole area would still be the same.
Sorry, I have absolutely no idea what you are trying to say. (But I assume you mean "volume" not "area")

the overall density of the whole area would still be the same.

Do you mean: if you take the volume of the original star and the mass of the black hole, then the (average) density will be the same as the original star?

If so, roughly yes. Actually somewhat less, as a significant proportion of the mass of the star will have been blown away in the supernova explosion.

Similarly, at a given distance form a black hole, the gravitational force of the black hole will be exactly the same as a star of the same mass. For example, if the sun suddenly became a black hole, it would make no difference to the orbit of the Earth (although it would get very cold and dark...

29. Originally Posted by Strange
Originally Posted by curious mind
i meant the the whole area, not only the area where the star has been. even though the density, where you now have the black hole, is higher with a smaller radius; than what the sun had before. the overall density of the whole area would still be the same.
Sorry, I have absolutely no idea what you are trying to say. (But I assume you mean "volume" not "area")

the overall density of the whole area would still be the same.

Do you mean: if you take the volume of the original star and the mass of the black hole, then the (average) density will be the same as the original star?

If so, roughly yes. Actually somewhat less, as a significant proportion of the mass of the star will have been blown away in the supernova explosion.

Similarly, at a given distance form a black hole, the gravitational force of the black hole will be exactly the same as a star of the same mass. For example, if the sun suddenly became a black hole, it would make no difference to the orbit of the Earth (although it would get very cold and dark...
we mean the same thing.

so when a star becomes a black hole, even considering the amount of mass that gets blasted into space, proportional you'll have an area with a smaller radius (more room) but with the same density on average still.
with on average i meant, up to where the blown away mass of the exploded sun reached.

if that mass got i.e. blasted 5 lys away from the sun, the average densite within that 5 lys radius is the same still. even though it changed drastically in the area of the former sun.

30. Originally Posted by curious mind
if that mass got i.e. blasted 5 lys away from the sun, the average densite within that 5 lys radius is the same still. even though it changed drastically in the area of the former sun.
No. If the mass is distributed over a VOLUME (*) of 5 light years radius then the density would be a tiny fraction of what it was before.

(*) Write out one hundred times: I must not write "area" when I mean "volume".

31. lol.

no i mean the density in that 5 ly radius would be same before the explosion as after on average.

I must not write "area" when I mean "volume". I must not write "area" when I mean "volume". I must not write "area" when I mean "volume". I must not write "area" when I mean "volume". I must not write "area" when I mean "volume". I must not write "area" when I mean "volume". I must not write "area" when I mean "volume". I must not write "area" when I mean "volume". I must not write "area" when I mean "volume". I must not write "area" when I mean "volume". I must not write "area" when I mean "volume". I must not write "area" when I mean "volume"... to be continued

32. Originally Posted by curious mind
lol.

no i mean the density in that 5 ly radius would be same before the explosion as after on average.
Yes it would. Roughly: with the caveat that some of the mass will have been turned into energy (photons) and neutrinos. These will have been moving at the speed of light (very slightly slower for neutrinos) and so will be a long way outside the 5 light year radius. But this will be quite small percentage of the total mass.

33. yes, ok, so now you have 30km radius black hole where a 700.000km radius sun was before. so the "room" in that "volume"will now get occupied by space?

34. Originally Posted by curious mind
yes, ok, so now you have 30km radius black hole where a 700.000km radius sun was before. so the "room" in that "volume"will now get occupied by space?
You seem to be thinking of "space" as some sort of fluid that will rush to fill the gap left by matter when it is moved. There is no more or less "space" or "room" than before. (Although space-time around and inside the black hole will be more extremely curved than it was before.) Unless you are defining "room" as space not filled by matter...

But extra credit for taking things a step at a time and making your ideas clear(er)

35. Originally Posted by Strange
Originally Posted by curious mind
yes, ok, so now you have 30km radius black hole where a 700.000km radius sun was before. so the "room" in that "volume"will now get occupied by space?
You seem to be thinking of "space" as some sort of fluid that will rush to fill the gap left by matter when it is moved. There is no more or less "space" or "room" than before. (Although space-time around and inside the black hole will be more extremely curved than it was before.) Unless you are defining "room" as space not filled by matter...

But extra credit for taking things a step at a time and making your ideas clear(er)
ty

but something has to be there then, i.e. a comet or asteroid that would have crashed into the sun, can now pass through that area?
or is that "volume" the event horizon now? where it would still pull the comet/asteroid towards it?

36. Originally Posted by curious mind
but something has to be there then, i.e. a comet or asteroid that would have crashed into the sun, can now pass through that area? or is that "volume" the event horizon now? where it would still pull the comet/asteroid towards it?
VOLUME!

I'm still not quite sure what you are thinking. There is a fixed "amount" of space within your 5ly volume. You can calculate how much there is from the "schoolboy" equation [tex]\frac{4}{3} \pi r^3{/tex] (1). That does not change when a star collapses to a black hole (2). But less of it is filled with matter.

(1) hope I got that right after the schoolboy comment ...
(2) A fully accurate analysis using General Relativity might disagree with that. After all, the volume inside the black hole's event horizon is (arguably) no longer part of our universe.

37. Originally Posted by Strange
Originally Posted by curious mind
but something has to be there then, i.e. a comet or asteroid that would have crashed into the sun, can now pass through that area? or is that "volume" the event horizon now? where it would still pull the comet/asteroid towards it?
VOLUME!

I'm still not quite sure what you are thinking. There is a fixed "amount" of space within your 5ly volume. You can calculate how much there is from the "schoolboy" equation [tex]\frac{4}{3} \pi r^3{/tex] (1). That does not change when a star collapses to a black hole (2). But less of it is filled with matter.

(1) hope I got that right after the schoolboy comment ...
(2) A fully accurate analysis using General Relativity might disagree with that. After all, the volume inside the black hole's event horizon is (arguably) no longer part of our universe.

no, i mean the sun, before becoming a black hole, had a 700.000km radius. now there's only a 30km radius blackhole, in that same "volume"

if you were in a spaceship, you had to fly around the sun (the 700.000km radius). but now, with only a 30km radius black hole, you could travel in a straight line?

matter/light/whatever has more freedom to move now, or not?

38. Space and room are not the same as has been pointed out to you. Space consists of (nominally) empty space and space with matter in it. Either way it is still space.

39. Originally Posted by John Galt
Space and room are not the same as has been pointed out to you. Space consists of (nominally) empty space and space with matter in it. Either way it is still space.
yes, and now that that huge sun got turned into a tiny black hole, i'll end up with more space?

40. Originally Posted by curious mind
no, i mean the sun, before becoming a black hole, had a 700.000km radius. now there's only a 30km radius blackhole, in that same "volume"
But the volume is the same. Less of it is filled by the sun (now a black hole).

if you were in a spaceship, you had to fly around the sun (the 700.000km radius). but now, with only a 30km radius black hole, you could travel in a straight line?
As I say, the gravitational effect is the same. If you were orbiting the sun then you could continue to orbit the black hole at the same distance. But (and maybe this is what you are getting at) you could orbit the black hole at a distance where you would once have been deep inside the sun.

Note that there is a distance near the black hole where you can no longer orbit (orbital velocity becomes greater than the sped of light).

matter/light/whatever has more freedom to move now, or not?
Yes, in the sense that you can go to places that were formerly full of sun-stuff. So there is more "empty space" (but no more space).

41. Originally Posted by curious mind
Originally Posted by John Galt
Space and room are not the same as has been pointed out to you. Space consists of (nominally) empty space and space with matter in it. Either way it is still space.
yes, and now that that huge sun got turned into a tiny black hole, i'll end up with more space?
No. In the first case you have a volume of space that we shall say is 50% star and 50% vacuum. (I'm ignoring radiation, magnetic fields, virtual particles, solar wind, etc). Let's say that volume of space is 2 x 10^18 cubic kilometres.

Now the star collapses. That volume of space is occupied by 2% star and 98% vacuum, but the volume of that space remains 2 x 10^18 cubic kilometres. There is now more vacuum, but vacuum does not equal space. Room does not equal space.

Please identify what is unclear in this explanation.

42. Originally Posted by Strange
Originally Posted by curious mind
no, i mean the sun, before becoming a black hole, had a 700.000km radius. now there's only a 30km radius blackhole, in that same "volume"
But the volume is the same. Less of it is filled by the sun (now a black hole).

if you were in a spaceship, you had to fly around the sun (the 700.000km radius). but now, with only a 30km radius black hole, you could travel in a straight line?
As I say, the gravitational effect is the same. If you were orbiting the sun then you could continue to orbit the black hole at the same distance. But (and maybe this is what you are getting at) you could orbit the black hole at a distance where you would once have been deep inside the sun.

Note that there is a distance near the black hole where you can no longer orbit (orbital velocity becomes greater than the sped of light).

matter/light/whatever has more freedom to move now, or not?
Yes, in the sense that you can go to places that were formerly full of sun-stuff. So there is more "empty space" (but no more space).

this is what get's me. i have more empty space, but not more space?

i'm not saying or meaning, that the gained "empty space" is expansion of space. but i.e. if i replace an ant of a 2D surface(space) with a dust particle, ... OMG, now i see i have more "ROOM". ok, if i replace "space" with "ROOM", i got it right?

43. Originally Posted by John Galt
Originally Posted by curious mind
Originally Posted by John Galt
Space and room are not the same as has been pointed out to you. Space consists of (nominally) empty space and space with matter in it. Either way it is still space.
yes, and now that that huge sun got turned into a tiny black hole, i'll end up with more space?
No. In the first case you have a volume of space that we shall say is 50% star and 50% vacuum. (I'm ignoring radiation, magnetic fields, virtual particles, solar wind, etc). Let's say that volume of space is 2 x 10^18 cubic kilometres.

Now the star collapses. That volume of space is occupied by 2% star and 98% vacuum, but the volume of that space remains 2 x 10^18 cubic kilometres. There is now more vacuum, but vacuum does not equal space. Room does not equal space.

Please identify what is unclear in this explanation.
you're allowed to hammer a nail into my head, to give my brain more "SPACE", because the "ROOM" is too small for thoughts to travel through.

i think i got it now.

44. Originally Posted by curious mind
OMG, now i see i have more "ROOM". ok, if i replace "space" with "ROOM", i got it right?
I think that will do.

But just to confuse you even more ... A Black Hole is a Waterfall of Space

45. Originally Posted by Strange
Originally Posted by curious mind
OMG, now i see i have more "ROOM". ok, if i replace "space" with "ROOM", i got it right?
I think that will do.

But just to confuse you even more ... A Black Hole is a Waterfall of Space
ok i haven't start reading, but looking at the picture, that was my thought all along. i don't know, if it went in the right direction; because off too less "ROOM", but because of density and energy being compressed.

46. ok, i get the outside of horizon = less than c, i also get the at horizon = c ... but then how does it get to = >c?

if the fish at the horizon, no matter how hard it tries, can't move, how it changes to: moving, whether you like it or not?

47. Originally Posted by curious mind
ok, i get the outside of horizon = less than c, i also get the at horizon = c ... but then how does it get to = >c?

if the fish at the horizon, no matter how hard it tries, can't move, how it changes to: moving, whether you like it or not?
nevermind, read it wrong ... again. i had the image of a fish swimming upstream against the flow and then wondering,what would stop him swimming downstream with the flow.

48. In this model (and remember it is just a model, there isn't actually any "space-stuff" falling in) space falls in at an accelerating rate, just like anything falling in a gravitational field.

It continues to accelerate past the event horizon - note that it is not being gravitationally attracted by the event horizon but by all the mass concentrated at the centre of the black hole.

The old cliché that "nothing can move faster than c" doesn't apply here because we are talking about "space" falling, not an object moving.

The fish can never move faster than c (because it is an object) and so cannot swim "upstream" fast enough to avoid being taken to the center of the black hole.

49. Originally Posted by curious mind
nevermind, read it wrong ... again. i had the image of a fish swimming upstream against the flow and then wondering,what would stop him swimming downstream with the flow.
I'ts all very well saying "never mind" when I have already written a reply. Sigh.

50. Originally Posted by Strange
Originally Posted by curious mind
nevermind, read it wrong ... again. i had the image of a fish swimming upstream against the flow and then wondering,what would stop him swimming downstream with the flow.
I'ts all very well saying "never mind" when I have already written a reply. Sigh.
so space itself falls in? like, if i'd use a strong vaccum cleaner on the 2D ballon surface? from beneath the surface.

lol sorry, pictured it wrong.

51. ok, i'm sorry, now i have more questions; but i need a break first. and that video is scary.
just to imagine, that is the last thing you see, before your ears and toes become one.

52. if space itself falls in, it means that either the remaining matter of the sun became too heavy proportional to the surface it "sits" on OR spins/rotates so fast, that it takes the space/surface along?

i.e. if i place a tablecloth over a table, where i have cut a hole in before. if i now drop a ball, being heavy enough, over that hole; it would fall and fall until it hits the ground, taking the tablecloth with it.
OR
it rotates so fast, that it actually twists space?

53. Strange, where are you?

54. Originally Posted by curious mind
Strange, where are you?
I just had to pop through the event horizaon to see what was going on. Had a bit of a job getting back out again...

Originally Posted by curious mind
if space itself falls in, it means that either the remaining matter of the sun became too heavy proportional to the surface it "sits" on OR spins/rotates so fast, that it takes the space/surface along?

i.e. if i place a tablecloth over a table, where i have cut a hole in before. if i now drop a ball, being heavy enough, over that hole; it would fall and fall until it hits the ground, taking the tablecloth with it.
OR
it rotates so fast, that it actually twists space?
I'm not quite sure what you are asking. There is a critical radius for a given mass where, if the mass is entirely within that radius, it will form a black hole.

Note that in this waterfall model, "space fall" into all masses. It is just that with a black hole it falls faster than c.

There is a "twisting" effect as well. A rotating mass will "drag space" around with it. This is called frame dragging or the Einstein-Lense-Thirring Effect. It has been measured around Earth by a satellite called Gravity Probe B.

55. wow, so i had it right.
also, do black holes grow or shrink? oh and another thing, why isn't a black hole considered as part of the universe?

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