The Largest Known Star

[Digit]

Maths tends to be used in support of an idea Shark not produce it.
Try this!.
If the angular momentum of the star is maintained then its rotational time must decrease when it collapses.
Can a spherical shape be maintained under those circumstances? I suggest not.

[Forum Monk]

Astrophysics is not my field, Digit, although I have a basic working understanding of the concepts. I think you have raised some interesting questions. I will do some reading and see if I can come up with some answers.

[Digit]

I hope you can Monk. Whilst you're at it see what comes up about Black Holes. I won't give my reasoning here but I suspect that someone will have sugested that a black hole would look like an old LP disc.

[CShark]

Maths tends to be used in support of an idea Shark not produce it.

Perhaps I was not clear when I stated that math was not my stong point. If I could work out the differences in gravitation vs mass, I would be producing a conclusion or result, where I did not have one to begin with. Yes, it also supports an idea, but in this case, I have no idea how it would turn out.

[CShark]

Try this!.
If the angular momentum of the star is maintained then its rotational time must decrease when it collapses.
Can a spherical shape be maintained under those circumstances? I suggest not.

Ok, I'm going to show my complete lack of understanding of physics here: as the star collapses, would it's spin not increase ? If you have a ball on a rope, spinning over your head, the speed at the centre is greater than at the end of the rope...also, I believe neutron stars spin at an exceedingly high rate. Hmm..do quasars spin very quickly as well ? I believe they do (anyone know this ?)

So, to answer your question, IF the rate slowed, then yes, the spherical shape would distort. But as (I believe) the opposite is true, the collapsing star would still be a sphere.

[CShark]

I hope you can Monk. Whilst you're at it see what comes up about Black Holes. I won't give my reasoning here but I suspect that someone will have sugested that a black hole would look like an old LP disc.

Probably something by Elvis.....

[Digit]

Ok, I'm going to show my complete lack of understanding of physics here: as the star collapses, would it's spin not increase ?

Indeed. That is what I stated, I said its rotational time would decrease, ie, the revs would rise. Increasing spin speed then creates a battle between centrifugal force trying to flatten the mass into a disc versus gravity trying to hold it as a sphere.
Which one would win?
Returning to the subject then of gravity of a Black Hole being the same or not as that of the star that produced it begs this question. If the star didn't pull everything into itself, why would the susequent Black Hole do so?
When the star collapses the planetary system is no longer pushed away by radiation pressure 'cos the star is no longer radiating, but is radiation pressure that strong? Does the gravity well deepen as the mass is crushed ever closer? Is Dark Matter involved here?

[CShark]

Indeed. That is what I stated, I said its rotational time would decrease, ie, the revs would rise. Increasing spin speed then creates a battle between centrifugal force trying to flatten the mass into a disc versus gravity trying to hold it as a sphere.

Sorry Dig, I took a pain killer before logging in..and misread your message. Really have to see about getting better drugs...

[Forum Monk]

In general, I am a bit perplexed by your speculation on spinning black holes being disk shaped. Especially, since by defintion a true black hole is a singularity and therefore shapeless. Now it seems unlikely that a true singularity could possibly exist and much of what I read in recent years discounts them to some degree. Nevertheless there is a measurable event horizon. Now if you went through the entire link I posted previously from Universe Today, you would realize that black holes can form in different ways and not all of them begin life as ordinary stars. Stars spin. Collapsing gas, not necessarily. Somewhere just over the event horizon, conventional physics breaks down and so, I speculate, the laws of conservation of momentum do as well. I have read speculations of different shapes for different types of black holes assuming we define that matter which surrounds the black holes as a physical part of the black hole.

We do believe that observed accretion disks are spinning (or spiraling) around black holes. We have seen these disks in infrared and X-ray bands and suspect that a black hole exists in the core. These resemble your spinning LPs, however the hole through which you mount the disk on your turntable is more suggestive of the black hole and not the disk itself.

[Forum Monk]

then all stars should be about the same mass at the time they light up.

I think the problem in your reasoning is the isolated quotation above. They are not all the same mass when they ignite. However, the reasons why they are not can be too complicated to discuss or understand with any degree of certainty. There are many forces at work, especially in crowded star forming regions and though many researchers have their pet theories, I doubt there is an academic concensus,

[Digit]

I haven't done any research on these matters Monk, frankly I've been too busy, just thinking out loud and reasoning.
One of the problems with that course of action is the question of whether our familiar physis still apply under the sort of conditions exisiting 'in' and around a black hole.
Unfortunately, as far as I understand this, nobody knows, therefore till we have a definitive answer I think we must work on the basis that we are dealing with familiar physics.
From that a singularity is an impossibility, an acedemic solution, a mathematical entity. According to Einstein mass cannot be destroyed, if you crush the mass of a large star till all known space within its structure is eliminated its mass will remain the same, as apparently demonstrated by its continuing gravitational well.
Also if our known physics do pertain then there will be a definite size to a black hole, its size dependent on the mass of the parent star and a disc rather than a sphere is likely. I would point out my friend that that which does escape from a black hole, as X rays, for example is supposed to escape from its poles, that would support the idea of a disc as gravity would have to be less there than across the disc.
Agreed all this depends on the application of logic and familiar practices, if our known physics break down, then of course we are in a different ball game.
If I get some time later I will enjoy reading through your references but at the moment my daughter-in-law is in hospital undergoing emergency surgery and the wife and I are busy looking after the family, it's all go here!

[CShark]

Thinking out loud as well, although the definition of a singularity is a point, and therefore having no physical dimentions, as it cannot be proven why do we suspect that black holes are indeed singularities ? From what I gather, most if not all galaxies contain 'super massive' black holes at their nucleus. Are astronomers referring to the event horizon, or are they saying the 'hole' is indeed 'X' light years across ?

[Digit]

Shark, I think you're after my title of Les enfant terrible! Welcome to the akward club!

[War Arrow]

According to Einstein mass cannot be destroyed, if you crush the mass of a large star till all known space within its structure is eliminated its mass will remain the same, as apparently demonstrated by its continuing gravitational well.

This probably doesn't help, and may have only vague relevance to the main point, and its no doubt even less helpful that I can't be arsed to go upstairs and find the issue of New Scientist in which I saw this mentioned but... it is my understanding that one current theory pertaining to black holes is that their mass gradually decreases over time due to their absorbing some particle or other which has negative mass, thus resulting in the bizzare idea that adding negative mass decreases positive mass (bizarre in terms of reality behaving exactly like maths in this instance, I guess).

I'll get me coat.

[Forum Monk]

it is my understanding that one current theory pertaining to black holes is that their mass gradually decreases over time due to their absorbing some particle or other which has negative mass, thus resulting in the bizzare idea that adding negative mass decreases positive mass (bizarre in terms of reality behaving exactly like maths in this instance, I guess).

I haven't heard this. It brings up interesting questions about the theoretical lifetimes of these objects, however. How old can a black hole be and if keeps gobbling mass does it continue to enlarge or does the mechanism you described keep it in check?

Thinking out loud as well, although the definition of a singularity is a point, and therefore having no physical dimentions, as it cannot be proven why do we suspect that black holes are indeed singularities ?

I am not sure the singularity defines a single point. Merely a lump of mass which has no space. Nevertheless it occupies space and so has dimension. If this were not so, it would be pure energy, but energy (AFAIK) does not bend space.