Is Dark Matter really necessary?

[Lazarus]

The primary evidence for Dark Matter is the observation that many distant galaxies have stars rotating at pretty much the same velocity.  Perhaps the structure of the galaxies can explain the phenomena.

 

A galaxy with most of the matter near the center of the galaxy would have the orbiting outer stars with a lower velocity than the inner stars. 

 

However, with a disc shaped galaxy with evenly spaced stars, the outer stars would have a higher velocity than the inner stars.  The reason is that the orbit of a star is not affected by evenly spaced stars further from the center of the galaxy.  The calculation of the relative velocities of stars in the disc is:

 

A is the gravitational acceleration.

F is the centripetal force.

M is the total mass of the stars closer to the center of the galaxy.

V is the velocity of a star.

D is the distance from the star to the center of the galaxy.

 

M = D^2

A = M/D^2

F = V^2/D

A = F

M/D^2 = V^2/D

D^2/D^2 = V^2/D

1 = V^2/D

V^2=D

V = D^.5

 

So the velocity of the stars increases by the square root of the distance.

 

At some configuration of the stars the velocity would be the same for all stars.  One example is a tapered disc with the density of the stars inversely proportional to the square root of the distance from the center of the galaxy. That causes mass to become M = D and V^2 = 1.  All the stars now have the same velocity.

 

Is this correct?

Edited July 27, 2018 by Lazarus

[Strange]

31 minutes ago, Lazarus said:

Is this correct?

I haven't checked your maths, but you are correct in principle. The trouble is that the observed distribution of stars doesn't match that required for the rotation curves.

This also doesn't address the other evidence for dark matter.

[Lazarus]

Excellent point.  Is there a convenient place to find the distribution of the stars and gas?

[J.C.MacSwell]

43 minutes ago, Lazarus said:

 

 

However, with a disc shaped galaxy with evenly spaced stars, the outer stars would have a higher velocity than the inner stars.  The reason is that the orbit of a star is not affected by evenly spaced stars further from the center of the galaxy. 

 

This is essentially true if there is an evenly spaced spherical distribution, not for an evenly spaced disc distribution.

[Strange]

I'm not sure. You might want to ask at http://forum.cosmoquest.org - it is populated by professional and amateur astronomers, astrophysicists, etc. But they have very strict rules so be careful how you ask the question so you don't appear to be promoting a non-mainstream theory. Good luck.

[Lazarus]

4 minutes ago, J.C.MacSwell said:

This is essentially true if there is an evenly spaced spherical distribution, not for an evenly spaced disc distribution.

What if you considered a slice of the sphere?  What force would apply to the star?

[J.C.MacSwell]

5 minutes ago, Lazarus said:

What if you considered a slice of the sphere?  What force would apply to the star?

It would be attracted more to the near stars without full compensation from the greater number of distant stars in the disc (or whatever you call a disc with the centre disc removed)

Generally this should be a net drag affect on the star in question.

Edited July 27, 2018 by J.C.MacSwell

[Lazarus]

3 minutes ago, J.C.MacSwell said:

It would be attracted more to the near stars without full compensation from the greater number of distant stars in the disc (or whatever you call a disc with the centre disc removed)

Generally this should be a net drag affect on the star in question.

Doesn't that imply that a spherical configuration would cause the outer mass to affect the star?

[J.C.MacSwell]

9 minutes ago, Lazarus said:

Doesn't that imply that a spherical configuration would cause the outer mass to affect the star?

No.  The missing pieces of the hollow sphere would have the exact opposite affect, such that all put together it sums to zero net force.

[Strange]

11 minutes ago, Lazarus said:

Doesn't that imply that a spherical configuration would cause the outer mass to affect the star?

No, Newton's Shell Theorem shows that the only the gravitational mass within the orbit s relevant.

The same is basically true, I think, for the disk of the galaxy for orbits in the disk. Calculating the orbital speeds above and below the disk (e.g. for the gas and dust that provides some of the evidence for dark matter) is somewhat more complex.

 

[J.C.MacSwell]

19 minutes ago, Strange said:

No, Newton's Shell Theorem shows that the only the gravitational mass within the orbit s relevant.

The same is basically true, I think, for the disk of the galaxy for orbits in the disk. Calculating the orbital speeds above and below the disk (e.g. for the gas and dust that provides some of the evidence for dark matter) is somewhat more complex.

 

Only true for a homogenous spherical mass distribution.

[Strange]

3 minutes ago, J.C.MacSwell said:

Only true for a homogenous spherical mass distribution.

A "shell" is not homogeneous! 

But it is a good approximation in many other cases.

[J.C.MacSwell]

10 minutes ago, Strange said:

A "shell" is not homogeneous! 

But it is a good approximation in many other cases.

My point is that it doesn't hold for a ring. You need the rest of the spherical shell as well or it doesn't work. If you were inside a ring, you would be attracted to the nearest part of it. So for a disc Galaxy you can't ignore what is outside of the orbit.

Edited July 27, 2018 by J.C.MacSwell

[Lazarus]

2 hours ago, J.C.MacSwell said:

My point is that it doesn't hold for a ring. You need the rest of the spherical shell as well or it doesn't work. If you were inside a ring, you would be attracted to the nearest part of it. So for a disc Galaxy you can't ignore what is outside of the orbit.

Thank you for pointing that out.  It certainly does complicate the calculation.  The contribution from the outer stars would cause the stars close to the center to have a lower velocity but the outer stars would be affected less.  That would leave the outer stars with a higher velocity than the inner stars.  To reach equal velocities, the density of the stars would have to decrease more rapidly.

3 hours ago, Strange said:

I haven't checked your maths, but you are correct in principle. The trouble is that the observed distribution of stars doesn't match that required for the rotation curves.

It appears there is some disagreement about the structure of galaxies.  Here is an article that seems to contend that the structure can match the velocities.

https://www.sciencedaily.com/releases/2016/09/160921085052.htm

 

Date:

September 21, 2016

Case Western Reserve University

Summary:

Researchers have found a significant new relationship in spiral and irregular galaxies: the acceleration observed in rotation curves tightly correlates with the gravitational acceleration expected from the visible mass only. The discovery may alter the understanding of dark matter and the internal dynamics of galaxies.

[mathematic]

Dark matter has other evidence besides rotation of stars within galaxies.  The relationship between galaxies in clusters seems to need dark matter.  Astronomers have been able to map dark matter distributions.  Current cosmology theory indicates that there isn't nearly enough ordinary matter for galaxies to form.

[Strange]

24 minutes ago, Lazarus said:

It appears there is some disagreement about the structure of galaxies.  Here is an article that seems to contend that the structure can match the velocities.

https://www.sciencedaily.com/releases/2016/09/160921085052.htm

 

 

Date:

 

September 21, 2016

Case Western Reserve University

 

Summary:

 

Researchers have found a significant new relationship in spiral and irregular galaxies: the acceleration observed in rotation curves tightly correlates with the gravitational acceleration expected from the visible mass only. The discovery may alter the understanding of dark matter and the internal dynamics of galaxies.

Interesting. I haven't seen this before. It still has the problem of all the other evidence for dark matter though ...

 

OK. Just found a better article about that research. It doesn't mean there is no dark matter (as I understood from the first article) but that the amount of dark matter is strongly correlated with the distribution of the visible matter. (I think I have seen this result before). A better overview here: https://physics.aps.org/articles/v9/130

[Lazarus]

1 hour ago, Strange said:

OK. Just found a better article about that research. It doesn't mean there is no dark matter (as I understood from the first article) but that the amount of dark matter is strongly correlated with the distribution of the visible matter. (I think I have seen this result before). A better overview here: https://physics.aps.org/articles/v9/130

These two statements from your suggested article seem to say the rotation matches the visible mass.

“Arthur Kosowsky, Department of Physics and Astronomy, University of Pittsburgh, 3941 O'Hara Street, Pittsburgh, PA 15260, USA

November 9, 2016• Physics 9, 130

A universal law shows that the rotation of a disk galaxy is determined entirely by the visible matter it contains, even if the disk is mostly filled with dark matter.”

---------

 

“From the 153 galaxies, the authors derive about 2700 data points of the predicted and actual acceleration at different radii within each galaxy’s disk. When plotted against each other, the predicted and measured accelerations trace out a tight relation: if you know the centripetal acceleration at a given radius expected from the gravity of the visible matter in the disk, you then also know the actual acceleration at that radius, even though in many cases it is mostly determined by the dark matter. “

---------

Also, if you let me arrange the stars in the galaxy, I will make the visible mass match the rotation.

[swansont]

17 hours ago, Lazarus said:

Is this correct?

Many of your equations fail dimensional analysis, so they are incorrect.

They may work as proportionalities, and you might accidentally come up with a correct trend.

But it does not match observation, or prediction for normal matter distribution.

https://en.wikipedia.org/wiki/Galaxy_rotation_curve#/media/File:M33_rotation_curve_HI.gif

Some rotation curves are flat after the initial rise.

 

[Strange]

11 hours ago, Lazarus said:

These two statements from your suggested article seem to say the rotation matches the visible mass.

It "matches" in the sense that it correlates with; not in the sense that it can be explained by. As the sentence you quote says: "even if the disk is mostly filled with dark matter"

What this seems to suggest is there is a very strong relationship between the amount and distribution of "normal" matter and the amount of dark matter. This may not be too surprising as the presence of dark matter is essential to galaxy formation. I don't know if this relationship has been confirmed by any of the simulations of structure formation (which require dark matter to reproduce the structures we see).

[Lazarus]

9 hours ago, swansont said:

Many of your equations fail dimensional analysis, so they are incorrect.

They may work as proportionalities, and you might accidentally come up with a correct trend.

But it does not match observation, or prediction for normal matter distribution.

https://en.wikipedia.org/wiki/Galaxy_rotation_curve#/media/File:M33_rotation_curve_HI.gif

Some rotation curves are flat after the initial rise.

 

Good to hear from you Tom.  You have been a great help correcting my many jumps to conclusions.

Why do I need dimensions when dealing with proportions ?

[swansont]

1 hour ago, Lazarus said:

Good to hear from you Tom.  You have been a great help correcting my many jumps to conclusions.

Why do I need dimensions when dealing with proportions ?

You didn't write them as proportions, you wrote them as equalities.

For example, you conclude that A=F. But F=ma

IOW we already know that force and acceleration  were proportional, but somehow you're showing that mass isn't involved. That should give you pause.

You assume that mass depends on area, but this is likely not linear, and gravity depends on mass and also distance, which you ignoring.

And you errors are confirmed, as your answer doesn't match the data.

[David Hine]

Hi, I raised the subject recently in the cosmology section showing that Hubble's Constant can now be calculated to be an unchanging and 'fixed' 70.98047 kilometres per sec per meg parsec. 

This has been pushed, without my awareness, to the 'speculations' area. I am not directly objecting to that, BUT does anyone here realise the 'big bang' model is also purely and extremely 'speculative'???? None of it is proven fact, and increasingly has to be 'fudged' to fit in with new data that the Astronomers are observing. Hence 'dark' matter / energy -fake concepts to 'balance the fake books of 'big bang'!!  That's NOT science in any way, but purely 'speculation', proving scientists do not understand very much about the universe, and certainly not its origin.

So my request, for this (to be a properly truthful scientific forum), anything to do with the 'big bang' hypothesis should also be moved to 'speculations'. To do that would take courage, but would earn great respect in the future when the 'big bang' hypothesis is finally consigned to the 'science bin of follies'.

Regards, David

[swansont]

21 minutes ago, David Hine said:

Hi, I raised the subject recently in the cosmology section showing that Hubble's Constant can now be calculated to be an unchanging and 'fixed' 70.98047 kilometres per sec per meg parsec. 

This has been pushed, without my awareness, to the 'speculations' area. I am not directly objecting to that, BUT does anyone here realise the 'big bang' model is also purely and extremely 'speculative'???? None of it is proven fact, and increasingly has to be 'fudged' to fit in with new data that the Astronomers are observing. Hence 'dark' matter / energy -fake concepts to 'balance the fake books of 'big bang'!!  That's NOT science in any way, but purely 'speculation', proving scientists do not understand very much about the universe, and certainly not its origin.

So my request, for this (to be a properly truthful scientific forum), anything to do with the 'big bang' hypothesis should also be moved to 'speculations'. To do that would take courage, but would earn great respect in the future when the 'big bang' hypothesis is finally consigned to the 'science bin of follies'.

Regards, David

!

Moderator Note

This is not the place for you to air grievances about mainstream physics, nor is it the place to advertise your pet theory — that is specifically called out in rule 2.10

Keep alternative science and your own personal conjecture to the appropriate forum (Speculations). Threads in the ordinary science forums should be answered with ordinary science, not your own personal hypothesis. Posting pet "theories" in mainstream science forums is considered thread hijacking.

 

[David Hine]

Don't you realise 'big bang' is pure speculation?? It's NOT proven science. So it's in the same category as 'The Principe of Astrogeometry', except that reveals the true Hubble value of 70.98047. The 'big bang' reveals only lies. that will lead to yet more lies

Also, why do you need to 'hide' behind an alias?? Are you guilty of something criminal, or ashamed to reveal your proper identity for some other reason?? That is certainly not the measure of an honest man or trusted scientist. Martin Rees talks utter crap, but he is honest (truly believing his nonsense), upright, and is certainly not a snivelling cowardly tick skulking 'in the dark' hiding behind an alias. I respect Martin for his honest, open, and good principles in life.

So, by that 'yardstick' this whole forum is fake, and it should all be put into the speculations bin. This is truth, but evil doers and liars prefer to skulk furtively in dark shadows, and deny truth.

Sadly, much of science today is corrupted by secret 'agendas' and 'grant grabbing' from public funds by tricking the 'holders of the purse', and not open and honest as it was 100 years ago. 

I'm glad I worked for the UK Military, and not in some dodgy and corrupt university conning public money for fake science projects. David Hine

The only thing you are capable of doing honestly is banning me, so please do that so I don't waste any more time here.

[StringJunky]

27 minutes ago, David Hine said:

Don't you realise 'big bang' is pure speculation?? It's NOT proven science. So it's in the same category as 'The Principe of Astrogeometry', except that reveals the true Hubble value of 70.98047. The 'big bang' reveals only lies. that will lead to yet more lies

Also, why do you need to 'hide' behind an alias?? Are you guilty of something criminal, or ashamed to reveal your proper identity for some other reason?? That is certainly not the measure of an honest man or trusted scientist. Martin Rees talks utter crap, but he is honest (truly believing his nonsense), upright, and is certainly not a snivelling cowardly tick skulking 'in the dark' hiding behind an alias. I respect Martin for his honest, open, and good principles in life.

So, by that 'yardstick' this whole forum is fake, and it should all be put into the speculations bin. This is truth, but evil doers and liars prefer to skulk furtively in dark shadows, and deny truth.

Sadly, much of science today is corrupted by secret 'agendas' and 'grant grabbing' from public funds by tricking the 'holders of the purse', and not open and honest as it was 100 years ago. 

I'm glad I worked for the UK Military, and not in some dodgy and corrupt university conning public money for fake science projects. David Hine

The only thing you are capable of doing honestly is banning me, so please do that so I don't waste any more time here.

Why don't you just stop posting instead of being banned? Doing nothing is easier than doing something.