Galaxy orbital velocities explained without 'dark matter' halos.
- Thread starter nebel
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No one is disputing that if the mass of the galaxy was distributed evenly then the outer limits of the galaxy would have a rotational period very close to the rotational period of the inner parts of the galaxy. That is precisely why the idea that the majority of the matter in the galaxy is unseen was developed.
Yes the calculations have been done. The visible amount of material and it's distribution indicate that the outer parts of the galaxies should be spinning much faster than the inner sections of the galaxy. That does not occur so calculating out how much mass would be required to be evenly distributed through the galaxy to get the outer arms to move close to the speed of the inner areas of the galaxy show that the amount of unseen matter is more than the matter that can be seen. There is either dark matter or the theory of gravity is wrong. Dark matter seems more likely.
origin, as to post 22: in an entity where the mass is distributed evenly , like NGC 7331 apod Dec 18 2014., The velocities in the inner orbits would fall to zero, and do so gradually commensurate with the mass remaining toward the center, but fall to zero nevertheless, whereas it would be at the maximum at the perimeter, with no halo needed at all. It would be a stunning zero at the center rising to the extreme at the fringes. It is this low inner velocity that I believe has been downplayed too much.
on #23. I like to see those calculation or a vulgarisation of them, and as I mentioned in my previous post #20, The dark areas between the star-rich arms are just as massive, only not glowing. The basic theory of gravity is not wrong, but most people are stunned when you prove to them that the center of gravity has no gravity at all, and areas adjacent very little to boot.
can you reference, link us these calculations you mentioned? thank you.
On dark matter= dark energy. Is it not now thought, that dark energy is a property of the void, space itself? if that were the case, there would not be more of it near toward the outside, adding to the nature of things, that mandate high gravity/velocities=energy there ?
on #23. I like to see those calculation or a vulgarisation of them, and as I mentioned in my previous post #20, The dark areas between the star-rich arms are just as massive, only not glowing. The basic theory of gravity is not wrong, but most people are stunned when you prove to them that the center of gravity has no gravity at all, and areas adjacent very little to boot.
can you reference, link us these calculations you mentioned? thank you.
On dark matter= dark energy. Is it not now thought, that dark energy is a property of the void, space itself? if that were the case, there would not be more of it near toward the outside, adding to the nature of things, that mandate high gravity/velocities=energy there ?
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origin, re: galaxy with even matter distribution; post #22: in such a body, the graphics presenting the velocities would be showing a Linear decline, a straight line from the top right corner, through the center and toward the left bottom end to negative max again.
( to show the reversal in the direction) .
This would be opposite of what we see in the Solar System - type situations, where the resultant falls from the maximum at sun's "surface" to near zero at the infinity distance.
The results of more or less flat velocity distributions we see in various galaxies are the are the result of the various uneven matter distributions, but in neither case should dark matter be needed to account for the data, in my POV.
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( to show the reversal in the direction) .
This would be opposite of what we see in the Solar System - type situations, where the resultant falls from the maximum at sun's "surface" to near zero at the infinity distance.
The results of more or less flat velocity distributions we see in various galaxies are the are the result of the various uneven matter distributions, but in neither case should dark matter be needed to account for the data, in my POV.
--?
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The visible mass is not distributed evenly in that galaxy.
The velocities do not fall to zero, if they did then the stars would fall into the black hole in the center of the galaxy. The stars near the center of our galaxy are moving incredibly fast compared to the stars in the rest of the galaxy.
A first year physics book will have all you need to understand this.
First of all I find it hilarious that you state there is no need for dark matter in the galaxy because there is dark matter in the galaxy.
Secondly that idea fails because there would be evidence of that amount of mass.
The only people stunned by this are people that have never taken physics.
That is because your point of view is from a position of ignorance. The observable mass in all galaxies is not evenly distributed, ergo there must be unseen matter that results in the velocity profiles seen.
Which means that the current cosmic theory , mainstream theory , is incomplete
Wow, you figured out that we do not know everything? Impressive.
Your admittance of the fact is even more impressive !!!!!
origin, I was referring to your 'theoretical galaxy' with even matter distribution, post 22. Clearly, a black hole in the center is not such. Look at a situation in globular clusters, mini galaxies, with no central mass, no common rotation, the stars in the central portion of their orbits are doing just fine with low velocities.
Rubin et al observed flat velocity distributions, until the black hole screamers were discovered.
Re: center of gravity without gravity: even academics swallow hard when confronted (in front of an audience) with that proposition/ essential fact.
I take exception to the use of the word "---ignorance" even if it describes reality. This idea was not put into pseudo science for nothing. Please offer some real refuting figures please, not platitudes.
Rubin et al observed flat velocity distributions, until the black hole screamers were discovered.
Re: center of gravity without gravity: even academics swallow hard when confronted (in front of an audience) with that proposition/ essential fact.
I take exception to the use of the word "---ignorance" even if it describes reality. This idea was not put into pseudo science for nothing. Please offer some real refuting figures please, not platitudes.
What do those have to do with what we were discussing? We were discussing how the rotational curve of galaxies does not match the visible matter distribution.
Don't be absurd. This is something that is covered in a first or second semester physics course.
You are the one who has the alternative hypothesis so don't just wave your arms lets see some calculations that support you conjectures.
What do those have to do with what we are discussing? such a "ideal" galaxy would be a starting point of calculations, discussion, and in an 'evenly distributed matter' normal matter situation, Peripheral orbit velocities are the highest.
Not all galaxies look like the Sombrero, that is why i posted APOD Dec 18, mentioned the smooth elipticals, the non-rotating star clusters.
You can pack a lot of more matter into the center, on top of the already evenly distributed matter, to lift that curve there to the level that naturally exists in the perimeter.
There seems to exist a circular reasoning too: we establish the amount of mass by looking at the velocities, not necessarily looking at what the gravity gradient should indicate there.
attempting to calculate any one of the myriads of galaxy configurations would by beyond my expertise. That is why I like your 'smooth matter' model as a starting point.
Not all galaxies look like the Sombrero, that is why i posted APOD Dec 18, mentioned the smooth elipticals, the non-rotating star clusters.
You can pack a lot of more matter into the center, on top of the already evenly distributed matter, to lift that curve there to the level that naturally exists in the perimeter.
There seems to exist a circular reasoning too: we establish the amount of mass by looking at the velocities, not necessarily looking at what the gravity gradient should indicate there.
attempting to calculate any one of the myriads of galaxy configurations would by beyond my expertise. That is why I like your 'smooth matter' model as a starting point.
They just found a galaxy without dark matter:
NASA/Goddard Space Flight Center. "Dark matter goes missing in oddball galaxy." ScienceDaily. ScienceDaily, 28 March 2018. <www.sciencedaily.com/releases/2018/03/180328130724.htm>.
One swallow does not make a summer, but needed adjustments in theories are discovered where the models fail.
NASA/Goddard Space Flight Center. "Dark matter goes missing in oddball galaxy." ScienceDaily. ScienceDaily, 28 March 2018. <www.sciencedaily.com/releases/2018/03/180328130724.htm>.
One swallow does not make a summer, but needed adjustments in theories are discovered where the models fail.
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Case of a disk, spiral galaxy: with equal distribution of matter, (which will not be the case, what with thousands of black holes holed up near the center), a gravity detector flying at 2 R, in the outer halo, would detect 8 times more "total gravity "* than when at 1/4 R.
* strength of the field x distance (circumference) through which it acts. Partially copied from main cosmology site.
think about that, in the halo, twice as far out then then " the perimeter", gravity is still as strong as it is only a quarter out from the center. in total 8 times more. (not corrected for density variation). and
we have not begun to figure in dark energ yet.
Case of a disk, spiral galaxy: with equal distribution of matter, (which will not be the case, what with thousands of black holes holed up near the center), a gravity detector flying at 2 R, in the outer halo, would detect 8 times more "total gravity "* than when at 1/4 R.
* strength of the field x distance (circumference) through which it acts. Partially copied from main cosmology site.
think about that, in the halo, twice as far out then then " the perimeter", gravity is still as strong as it is only a quarter out from the center. in total 8 times more. (not corrected for density variation). and
we have not begun to figure in dark energ yet.
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In a globular cluster, or elliptical, the surrounding imaginary sphere at 2R would constitute 64 times the gravity pulling compared in total to an even density 1/4 R inner sphere.
An unrelenting pull for an orbiting object to overcome with velocity.
If you upped the ante by having more stars present at any time near the center, does that change the strength at distance?
An unrelenting pull for an orbiting object to overcome with velocity.
If you upped the ante by having more stars present at any time near the center, does that change the strength at distance?
When applying the formula for surface of a sphere to origin's "2R, 1/4 g" dotted line, you can see that in the space surrounding a sphere, at 2 R there is 64 times the total gravity* of the inside, although at any given individual point on the outside at 2R there is the same g as at .25 R , and from there it is downhill endlessly to infinity. Thinking of an elliptical galaxy or globular star clusters here.
This is for a perfect sphere, situations for a perfect disk, pancake or Ravioli shaped body would vary
In the above graph, at ~ 8/10 of gravity and R, ( approximately as much down from the surface apex, than the 1/9 g line is up rom the r axis), there would be equal amount of total gravitational force in the inside than here is in the outside space.
Arrived at by having the volume of the inside ~ .8 R globe deducted from the volume of a ~1.04R outside globe, assuming that the strength of gravity is ~ equal in both spaces as the graph indicates, but that the parity, unity value is reached at half the distance outside than the distance down from the surface)
That equal at ,04 R ratio has risen to 1/64 inside /outside at 2R above the surface, and going to infinity should close the case.
Density gradient inside the globe would alter the ratios, but not in the general picture.
Let it be resolved then, that there is more gravity on the outside than the inside.
Arrived at by having the volume of the inside ~ .8 R globe deducted from the volume of a ~1.04R outside globe, assuming that the strength of gravity is ~ equal in both spaces as the graph indicates, but that the parity, unity value is reached at half the distance outside than the distance down from the surface)
That equal at ,04 R ratio has risen to 1/64 inside /outside at 2R above the surface, and going to infinity should close the case.
Density gradient inside the globe would alter the ratios, but not in the general picture.
Let it be resolved then, that there is more gravity on the outside than the inside.
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