1

New Theories / Re: Do Black Holes turn into something like Quark Stars?

« on: 31/01/2024 14:32:54 »

A value of, or approaching, infinite density can arise in two ways: (1) infinite mass in a finite volume or (2) finite mass in a zero volume. It was (2) that several posters were alluding to and the "infinite mass" in the singularity is an unfortunate misunderstanding by the OP.

2

New Theories / Re: Do Black Holes turn into something like Quark Stars?

« on: 31/01/2024 13:09:42 »

Hi.

and yet it seems there is a consensus towards infinity and zero which when you think about it is very counterintuitive.

   Stay calm and take a bit of time to read the replies if you want to.   When I first used this forum I had a lot of trouble keeping track of who was who.    You aren't always getting the "quote" system to work properly and sometimes it appears that a different contributor had said something from a different person - but that's ok,  the forum isn't easy to use and I know I got it wrong several times.   It can seem like a "them" vs. "me"  situation but it isn't.   "They" aren't collaborating, "they" are just people giving up some time and trying to help or join a discussion.   Indeed "they" will sometimes make mistakes and that includes me.   Sometimes there may be a few people with some other agenda, it's a public forum so anyone can use it.  You can usually spot people who are just trying to advertise something, for example.   If there's a big problem then there's a "report" button at the bottom of the post somewhere and you can have a moderator look at the post - you don't use that if the only problem was that you don't agree with them (it's meant for when the post has become threatening or breeched the policies etc).

   As far as I can see the following people have contributed to this thread so far:

You  ( @Airthumbs ).
@paul cotter
@Kryptid
@pzkpfw
@Halc
Me  ( @Eternal Student )

Of those only 2 have made any comments relating to size or density of the singularity.   One of those was me and I have tried to put the brakes on trying to measure the size or density of the singularity.   So that leaves only 1 who may have started to use this language and that isn't much of a consensus or majority.
 

Nearly all of the responses to my question have included information about a singularity being infinite and of zero size

     Only if you've also been discussing it on other forums or other places.
One of the phrases that has repeatedly come up in several replies is that  GR (General relativity) is only an approximation.  The appearance of a singularity at r=0 is certainly a concern and one of the main things that suggests GR is simply failing to describe this extreme situation and some new theory like a quantum theory for gravity may be required.

Best Wishes.

3

New Theories / Re: Do Black Holes turn into something like Quark Stars?

« on: 31/01/2024 00:50:25 »

Hi again,

Let's do some of your ( @Airthumbs ) later posts but a bit more quickly.

I read up on the Schwarzschild radius concept.  From what I can infer from the information it seems that this is used to define a black hole using the amount of mass it takes to create one.

No or not well phrased.

   R_s   =  2GM/c².

Given any mass, there is always a corresponding Schwarzschild radius.

If, at some time, you were in a situation where this mass, M, was concentrated in a spherical region of space with radius < R_s   then a Black Hole would form.    However, the formation of a black hole may also be inevitably if you had lower density of matter.    We require only that the self-gravity of the particle is sufficient to compress it to a radius equal to the Schwarzschild radius.

You took this bit from Wiki:

where density is defined as mass of a black hole divided by the volume of its Schwarzschild sphere

  and just need to be aware that this is a definition of convenience.    The Schwarzschild radius is a number with units of length,  so we can imagine a sphere in Euclidean geometry of that radius.   The Black hole has a mass parameter which is a number with units of  mass.   We can divide the two things and end up with another number which we can call density and has units of   mass per cubic metre.

   However, we need to notice these things:
    (i) The mass parameter of the black hole doesn't force the existance of some matter with that mass at the centre of the black hole.
    (ii)  The region described by  r<R_s  in a spacetime diagram was not a description of a spherical region of space.   Assuming GR and the Schwarzschild solution correctly describes spacetime, that r co-ordinate has now become a time-like co-ordinate.

   So this density parameter is just a number with units that match a physical density.   There need not be any matter with a physical mass M in this region and "this region" certainly isn't a spherical region of space with radius = R_s.    The density parameter may not be describing the physical density of anything.

    In a later post you took a quote from @Halc that said much the same things:

HALC "They don't have a density at all. For that, you'd need a meaningful volume. It does have a meaningful mass (that and charge and angular momentum. No more)".

    The only minor difference I would prefer is that Black Holes have a "mass parameter" rather than something that is definitely a mass.   However, the mass parameter grows by  m   if the the Black hole absorbs a particle of mass m,   so there is some one-to-one correspondance between the mass parameter of a black hole and the mass that may have gone in to make it.

Anyway, your Wiki density quantity for a BH is not necessarily describing the physical density of anything.   With that understanding some of your later comments almost evaporate:

So as a black hole gets smaller it must increase in density to maintain the Schwarzchild radius.

    There is no need to assume we were ever talking about the physical density of anything.

And in fact you cannot get a back hole with a smaller mass than Mt Everest according to Wiki anyway.

    I've not seen that article but I'll assume it was talking about how you might form a Black Hole starting from a situation where you just have some mass and space is reasonably Euclidean to begin with.    You can try to squash the matter together.   Your target density is 
(3 c⁶) / (32. π. G³ . M²)       or    proportional to   M^-2   if I've done my calculations correctly.
    So when you have more mass  (bigger M),  you don't have to squash it together as much to form a black hole.
I'll assume Wikipedia then assumes some physical limit on how much we can squash particles of matter together.

    That is interesting but just puts limits on our ability to make a Black Hole when we're out here in flat Euclidean space with only some ordinary matter and bit of equipment to play with.
    I don't suppose a Black Hole out in space with a mass parameter that is only half the mass of Mount Everest cares if we could have made it by squashing some stuff together or not.   As previously mentioned, the density parameter for this black hole is just a number that may not represent the physical density of any sort of object or material it is required to mainatin at its centre.

Best Wishes.

[and again.... I'm still too slow and more replies have appeared....]

Remember, all of the mass is concentrated into a singularity of zero size (this is why Halc says it doesn't have a meaningful density. Objects of zero size would have infinite density).

     hmmm... mostly OK.
     We know any particle of mass m cannot hold a constant radial co-ordinate r  once  r<R_s,  it must travel to the singularity at r=0 where its worldine terminates.    However r=0 is a non-removal singularity in the Schwarzschild solution.  The Schwarzschild metric does not apply at r=0 and I really have no way to determine the size of the event or point at r=0,  if indeed that is an event that exists in my universe.  Only if you say "stuff it, I'll just put the numbers in anyway" will you be able to argue that the mass all ends up in a region of space with 0 volume.

Halc said this:

They don't have a density at all. For that, you'd need a meaningful volume.

     I would imagine Halc is implying the radial co-ordinate  r   at the Schwarzschild radius,   just isn't a spatial co-ordinate - but you'd have to ask him.

Density is important for when an object becomes a black hole.

   Looks like general agreement with what has been said by myself above.

We need to differentiate the density of a black hole as its mass divided by the volume of the event horizon versus the density of the singularity.

     Really worried about trying to find the density of the singularity.
     It's sufficient to note that the density parameter Wiki suggested isn't describing a physical density of some material inside the event horizon.

What the wiki article is referring to is creating such a black hole from non-black hole matter (such as collapsing stars).

   ...and we're back on the same tracks and in general agreement.

Best Wishes.

4

New Theories / Re: Do Black Holes turn into something like Quark Stars?

« on: 30/01/2024 22:27:28 »

So from what I can tell from reading about this is that it actually seems to support the possibility that once the black hole does not contain enough mass to maintain the gravity well it's radius would become larger than its Schwarzschild radius and is no longer a black hole as light can then escape.

No, the event horizon radius would shrink in proportion to the shrinking in mass. Remember, all of the mass is concentrated into a singularity of zero size (this is why Halc says it doesn't have a meaningful density. Objects of zero size would have infinite density).

I found that in fact density is a vital part of calculation for the Schwarzschild radius of a black hole.  And in fact that to exist smaller black holes must have an increased density. The increased density ultimately sets the size limit of  black holes with smaller sizes based on the particles being squashed more, until we reach the limit of what can be squashed.

Density is important for when an object becomes a black hole. You can calculate the density of an object if all of its mass exists within its own Schwarzschild radius. However, it doesn't stay at that density. Since no force exists which can support a mass against such crushing force, it all collapses down into a singularity: an object of infinite density.

So as a black hole gets smaller it must increase in density to maintain the Schwarzchild radius.

We need to differentiate the density of a black hole as its mass divided by the volume of the event horizon versus the density of the singularity. All black hole singularities have the same density: infinite. What the wiki article is referring to is creating such a black hole from non-black hole matter (such as collapsing stars). It isn't referring to an existing black hole undergoing Hawking decay to become a smaller black hole.

The gravitational strength at the singularity is infinite is because the distances involved are zero. This is true for any finite value of mass. So even very tiny masses experience infinite gravitational force and thus the singularity cannot decrease its density to become something else.

However, all of these things are based on classical physics. It's quite possible that a black hole doesn't collapse to zero size due to quantum effects getting in the way. However, such a quasi-singularity would still be extremely small and extremely dense compared to anything else in the Universe.

5

New Theories / Re: Do Black Holes turn into something like Quark Stars?

« on: 30/01/2024 21:18:52 »

(I also started writing this yesterday in response to one of the very early posts you made.  I never got around to finishing it and posting it - but you ( @Airthumbs ) might as well have it ).

Hi.

Firstly, you should note that I'm not staff for the forum or anything special but I can spare an hour from my laundry duties and read your article.
Let's go through litle bits from the start.
     

We know there are two things that define the type of star we get, mass and density in space time.  I think I got that right!

     For main sequence stars, their mass and/or luminosity pretty much tells you everything.
     All you really have to tell us is just one thing - the mass of the star.  We can then find a model to predict the pressures and density at various depths into it and how this will change with time.

such as a neutron star. This is at a point where the density becomes so high that it overcomes the electrostatic repulsion between protons, allowing them to merge with electrons to form neutrons.

    Protons can combine with electrons (especially if anti-neutrinos are also available) to form neutrons.   There is no need for protons to get close to other protons for this process.    The main explanation given (for Neutron stars) is simply that there are too many electrons for such a small region of space and the Fermi exclusion principle will not allow two electrons to have the same quantum state.   There are protons available and it seems that the electrons will start combining with them to diminish the number of electrons occupying that space.

now I see a black hole as just another type of star, a star where the density, mass and pressure have reached a point where it causes the particles in the atoms to become so squashed together that it allows for the creation of this super dense object aka a black hole.

   OK,  that's speculation but not unreasonable and it could be like this.   If you assume that at least some of general relativity is right or a reasonable approximation for the spacetime around this dense object then some weird things are also going on.    You don't have to assume the GR model of a black hole is exactly right but at least be aware that time and space could be behaving quite strangely here.    As a result speculation about how these dense objects evolve with time, or move around in space can be quite wrong.
    We may all like to imagine a black hole as some simple object that behaves like a ball of stuff I can find in my back yard but nature just may not play by these rules.   It can have space and time behaving very oddly in this region.

and I think the idea of infinite mass is just silly.

    Not sure infinite mass was ever implied by anything.   Infinite density maybe.

However I say that is not the case and cannot be the case.

    That is an honest declaration of what is your opinion and you cannot be faulted for that.  Thank you.   Let's hear then what you think and why.....

What must happen is that after the density of the Black hole reaches a critical point, where the pressure is no longer able to maintain a singularity

     You don't explain how or why pressure would maintain a singularity and it's not obvious why it would.   Pressure does not cause or prevent a collapse of some material to a given region.  Pressure acts in all directions equally.   A pressure gradient is what you will need to cause a net flow of material from one place to another.   In the typical star, the pressure is greatest at the centre and falls off towards the outer surface, this causes an outward force that opposes further collapse of any material in toward the centre.   So a high pressure at or around the singularity may actually tend to push matter away from the centre rather than pulling matter there and maintaining a region of high density.

then the black hole, or black star as i like to think of it as, becomes a different type of star, one that is visible again

     No evidence presented or explanation for the how and why but OK... let's go on and see what you're thinking....

just maybe these newly discovered Quark stars might be the candidate I am postulating should exist.

     ...and this at least starts to imply the existance of something we might be able to find.   Can we find a star that is noticeably different to others and could have been an object that was a black hole and then evolved and switched on again as a star?   If we find one that will be great and some evidence in support of the ideas.
         There is already a theorised object called a "quark star" that you may have already seen or heard about (I don't suppose you would have used that term otherwise).   
(i)  It's theorised and not really supported with a lot of evidence yet.
(ii)  The evolution of a quark star is currently suggested to be from  Neutron star   to  a Quark star  and not something that happens via an intermediate stage that was a black hole.

if you have an area where the very nuclear bonds between atoms is overcome what would happen when they are able to reform those bonds under less extreme conditions?

    A theorised quark star shouldn't have recognisable atoms,  just some soup of quarks.   As such there may not be any inter-atomic bonds.

Overall Summary:
     The idea that some kind of matter remains inside "a region" we describe as the event horizon of black hole is not at all a silly idea and a lot of Astrophysicists may also harbour this view.   We can't get information out from anyone who has been in that region.   It may not be an ordinary region of just space which is why I put quotations around  "a region" (it's a region of spacetime and we won't worry too much about if it's just space).   Many physicists will assume that GR is just an approximation and it is going to break down somewhere.  Using it to predict what happens in a region of spacetime around  co-ordinate r=0 in a Black Hole is subject to some error.
     The remainder of your article is speculative but not offensive and not necessarily wrong.   It's very nice that you have an interest in the world around you and in Physics.
      Where you go from here is, of course, entirely up to you.   It may be worth keeping in mind that there is no shortage of "new ideas" or things that may revolutionise physics.   What is lacking are some extensions of existing theory, some demonstration of flaws in existing theory that may also lead to new discovery  and some new theory that is also well supported with experimental data or testing.

Best Wishes.

6

New Theories / Re: Do Black Holes turn into something like Quark Stars?

« on: 30/01/2024 20:41:19 »

Hi.

I want to clarify the following:

The consensus currently is that a black hole can exist with a mass of one gram?

Yes, pretty much true.    Hawking radiation from it may now be quite energetic and frequently emitted so that the Black Hole would be fairly short lived.

the scientific consensus, amongst whom I don't know, is that once a black hole is formed it remains as a black hole regardless of it's mass?

   Yes.   It can also grow if it absorbs more mass (or something with a mass parameter like another black hole).

The geometry referred to by a previous reply is simply the shape of the gravity well as a direct result of the presence of condensed matter,

    Sounds very much as if you're basing everything on models of Newtonian gravity.   Assuming Newtonian gravity then, yes, some dense matter should be at the centre of black hole.   If you don't assume Newtonian gravity but use GR instead then you don't need vocabulary like "gravity well", gravity isn't a force and the source of gravity is anything that provides a component to the stress-energy tensor.   So that mass is one source but pressure or a flux of momentum across a surface is also a suitable source.
     Finally we need to mention that simple Black Hole solutions such as the Schwarzschild solution for the Einstein Field Equations are actually vaccum solutions.  This is possibly a little complicated to explain but the important point is that they describe a solution in a region of spacetime where there is no source of stress-energy.   The Schwarzschild solution is static - the metric and curvature of spacetime does not change or depend on time.   GR doesn't need to care too much what may or may not have been the original cause of that curvature,  once such a curvature exists in a vcacum it will be static (unchanging with time).

I don't see how that remains unaltered when there is a change in mass

     It doesn't.   Black Holes have a mass parameter and if something with mass falls into a black hole then its mass parameter will change (see later for one example).   Also if some mass enters a region around a black hole then the Schwarzschild solution is no longer an exact solution for the region - as mentioned it's a vaccum solution so there cannot be any mass in the region.

If there is not enough mass to form that geometry then how can it maintain that shape?

    I'm not sure exactly what is being stated here.   If you change the mass parameter of a black hole then there is some change in the curvature of spacetime.   For example, a one solar masss BH has the space around it return to nearly flat Euclidean space over a short distance along the radial co-ordinate r.   A 100 solar mass BH  would still show significant curvature of space at this distance.    The "shape" is much the same but there is certainly some scaling.   Consider a graph of  y = 1/x   versus  y = 100/x.


graphs.jpg (225.62 kB . 1403x896 - viewed 300 times)

These have the same "shape" y=1/x  but the blue one is scaled (stretched) up the y-axis.   So the red graph looks flat enough at about x-axis position 12 units, while the blue one is still coming in with a significant gradient there.

If there is not enough mass to form that geometry then how can it maintain that shape?

     See above:
(i)  Changing the mass parameter of a BH maintains only the shape or geometry of spacetime but there is certainly some scaling.
(ii)  The Schwarzschild solution is a static solution of the EFE, it does not change or evolve with time.   That is interesting if you assume that "time" is some god-given thing that exists, it always is just one thing we could define and identify without reference to anything else like a metric or some frames of reference.  If you don't assume that then the result is less of a surprise.   
     When we go about solving the EFE (Einstein Field Equations) we do so without knowing exactly what our co-ordinates are going to mean or represent.  For the Schwarzschild solution we may naively assume they are something like spherical (r, θ, φ) co-ordinates for space (so r = a radial co-ordinate from the centre of the Black Hole and θ and φ are polar and azimuthal angles)  with t as a time co-ordinate.   However, we don't know exactly what the co-ordinates were representing until the full solution of the EFE is actually in our hands.   It turns out that the r co-ordinate is not a space-like co-ordinate everywhere.   When r < R_s  this co-ordinate is actually a time-like co-ordinate and  t becomes a space-like co-ordinate.   It is apparent that r and t are not the space and time co-ordinates we naively thought we might have when we began to obtain a solution to the EFE.       
    I know that's complicated so let's phrase it a different way:   You may be willing to accept that near a massive object time flows at a different rate to a place far away from the massive object.  You may also accept that time flows at different rates according to movement through space.   Time is not universal.    Once we have a black hole in close proximity, time has been morphed in various ways.  It just so happens that with respect to that time which we have around a black hole,  the curvature of space shows no change with time.   It is impossible to say that the Schwarzschild solution was unchanging with respect to some universal time or if it is just that time has been morphed so much around the black hole that any object in the vicinity of the black hole cannot observe any change in the curvature of space around the black hole.
     Anyway, you seem to be worried about whether the gravity around a black hole object should change with time.  It doesn't have to,  the Schwarzschild solution is a static (time unchanging) solution for the EFE in a vaccum.  It's not necessarily coincidence,  the black hole has "cheated" and morphed time to ensure this will happen.

Finally if black holes persist for such a long period of time and only end their lives in a wimpy pop of hawking radiation then we should be observing black holes of all sizes everywhere as they would be the most common cosmological entity.

    I don't know why you think they would have to be the most common - but they do seem to be fairly common.

(i)  Finding the big Black Holes:   When the LIGO gravitational wave detector was switched on, we thought we'd have to wait years to find anything but we didn't.   Within a few minutes (not sure of exactly how long but basically short), we found something.   Since then we've been finding plenty of clear examples of BH mergers every year.   

(ii) Finding the small ones:  This is actually much harder.   At a distance r > the tiny Schwarzschild radius,  a small black hole of mass parameter δm exerts no more force on something than some ordinary particle of the same mass δm.    However, small black holes are one candidate for dark matter.  We currently think dark matter makes up about 80% of the mass in the universe.  So maybe primordial Black holes are extremely prevalent.

[Various other replies have also come in while I've been writing this and doing stuff - sorry, there may be some overlap and existing answers or discussion already given  etc. ]

Best Wishes.

7

New Theories / Re: Do Black Holes turn into something like Quark Stars?

« on: 30/01/2024 16:40:14 »

The consensus currently is that a black hole can exist with a mass of one gram?

Yes.

If there is not enough mass to form that geometry then how can it maintain that shape?

Take a look at the formula for the Schwarzchild radius: https://en.wikipedia.org/wiki/Schwarzschild_radius

For any finite mass, a radius exists where an event horizon will form if that mass is concentrated inside of it. It's density that forms a black hole, not mass. However, that formula is a classical one, not taking into consideration the possible quantum effects that may put a lower limit on black hole mass.

do not require mass to exist?

No one said that a black hole of zero mass can exist.

Finally if black holes persist for such a long period of time and only end their lives in a wimpy pop of hawking radiation then we should be observing black holes of all sizes everywhere as they would be the most common cosmological entity.

It's quite possible that they are very common. However, they are also black. That means that only way we can observe them is through their gravitational effects (or if we get lucky enough that a stray, super-high energy particle from an evaporating black hole hits our detectors).

8

Physics, Astronomy & Cosmology / Re: If Andromeda is red shifted how can we collide with it?

« on: 28/01/2024 16:08:43 »

Andromeda is moving away from us as it is red shifted.  And yet we are going to collide with it. So how can we collide with an object that is red shifted?

It's blue shifted.

It should be blue shifted if it is heading our way regardless of the universe expansion.

It is.

If the local gravity is overcoming the expansion and that is the explanation for our collision then how can it be red shifted when we observe it?

It is blue shifted.

(local dynamics, such as the gravitational interaction between the Milky Way and Andromeda, cannot explain why Andromeda's light appears redshifted if it is indeed moving towards us).

It's blue shifted.