Solution to the Galaxy Rotation Problem, without Dark Matter

tashja said:
We apply American phrase ''close, but no cigar'' here, yes? :bawl:
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14 years ago I started learning Russian, but Google Translate is my friend now. I don't smoke, so no cigars at any time. But yes I don't think we were close, it was simply miles off.
 
This is interesting http://arstechnica.com/science/2012...the-closest-yet-to-the-milky-ways-black-hole/
"Fast-moving star is the closest yet to the Milky Way’s black hole"
Knowledge of complete orbits helps with modeling the black hole itself, which is invisible in IR light. While the data so far doesn't deviate from Newtonian gravity, observations over multiple orbits should allow for tests of general relativity in the region close to a black hole—something that hasn't been done yet using stellar orbits.
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Does that mean the flat rotational curves are not happening in the Milky Way galaxy?
 
We see the same rotational curve, but rekember how the Andromeda charts dive off quickly in the same few parsecs? The curve then flattens out in a strange way once we get out from the central bulge, around 5000 ly I think. The only reason we went straight for those blue stars in Andromeda, is because there would be the most drastic GTD we could encounter, and observe with relative certainty. The Milky Way imediately came to mind for me because we have physically watched, and so clocked geometricly, stars passing much faster, and much closer to our own Black Hole. That will be a good new place to start to learn what we can there eh?
 
Robittybob1 said:
Well I am skeptical still, for didn't you correct Scott and tell him gravity is proportional to mass. The planets are denser than the Sun aren't they (must check this)? Therefore the DM must have a greater effect on the planets rather the Sun. What stops the DM coming around us?
I don't know enough yet to argue the case, but DM is going to be studied when I get time.

Average density of Sun = 1,408 kg/m^3 way less than average density of the Earth which is roughly 5,515 kg/m^3
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You should be more concerned with the suns very large core which is a great deal denser and larger than the Earth is.
 
It seems obvious to me that most of the gravity of a galaxy such as the Milkyway is spread out in the disk of stars. It also seems obvious that the closer the stars are to central bulge or BH the faster they will be moving. If this was not so how would we ever get a spiral galaxy? Now consider even at the edge of our galaxy there is a lot of gravitational influence from the other stars in that region of the galaxy, and that means the stars there will be getting more gravitational assistance to there orbital speed.

I have often heard the example used as to why those rim stars are moving to fast is our own solar system. To me that's like comparing apples and oranges. If we had thousands of planets in a spiral around our sun, I'm sure the outer planets would be moving faster than they are now.
 
KilljoyKlown said:
It seems obvious to me that most of the gravity of a galaxy such as the Milkyway is spread out in the disk of stars. It also seems obvious that the closer the stars are to central bulge or BH the faster they will be moving. If this was not so how would we ever get a spiral galaxy? Now consider even at the edge of our galaxy there is a lot of gravitational influence from the other stars in that region of the galaxy, and that means the stars there will be getting more gravitational assistance to there orbital speed.

I have often heard the example used as to why those rim stars are moving to fast is our own solar system. To me that's like comparing apples and oranges. If we had thousands of planets in a spiral around our sun, I'm sure the outer planets would be moving faster than they are now.
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There is real important science here. Would it be possible for a Sun to have thousands of planets? It could have millions of asteroids but not thousands of planets. If there was too much matter in the proto-planetary disc the proto-star would stop collapsing, and and that might be where the process stops. No doubt this happens but as yet I haven't read about it. It would be like a MACHO and could be in part contributing to the dark matter of the galaxies. - failed proto-stars, partially collapsed nebulae - interesting.
 
KilljoyKlown said:
It seems obvious to me that most of the gravity of a galaxy such as the Milkyway is spread out in the disk of stars. It also seems obvious that the closer the stars are to central bulge or BH the faster they will be moving. If this was not so how would we ever get a spiral galaxy? Now consider even at the edge of our galaxy there is a lot of gravitational influence from the other stars in that region of the galaxy, and that means the stars there will be getting more gravitational assistance to there orbital speed.
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Not 'most' of the mass, since the central bulge, not core, holds about 1/6th the overall mass in a galaxy. It is more dense as we travel inward, just as it appears, neglecting any Dark Matter of course. Though there is a lot more mass distribution, compared to a planetary system for instance.

The signature spiral shape we see would happen if our velocities were exactly flat, i.e. if the stars all orbited at exactly 300 km/s you would still get this trailing appearance, and spiral affect. That is because if you think about the orbital period, if a star were twice as far out, but traveling the same distance over time it would still lag quite drastically, you see.

KilljoyKlown said:
I have often heard the example used as to why those rim stars are moving to fast is our own solar system. To me that's like comparing apples and oranges. If we had thousands of planets in a spiral around our sun, I'm sure the outer planets would be moving faster than they are now.
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I think we have pretty much figured out during the course of this topic that the expected curve does take this into account, the cumulative mass within each orbital sphere that is, but still falls short of solving the velocities observed. The example you usually see is the curve predicted for planets, but that is merely a simplistic way of showing the basic logic of the problem we are facing.
 
KilljoyKlown said:
You should be more concerned with the suns very large core which is a great deal denser and larger than the Earth is.
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Density, as far as orbital calculations are concerned, are only important if you can get closer to this super dense core, closer to the center of the mass. The closer you can get, the faster a stable orbit must be, and the stronger the Gravitational force, for lack of better words. When something is denser overall, or less dense overall, matters much since you cannot get any closer than the surface of either object. The overall density then has the greatest effect for potential gravitational influence.
 
Robittybob1 said:
There is real important science here. Would it be possible for a Sun to have thousands of planets? It could have millions of asteroids but not thousands of planets. If there was too much matter in the proto-planetary disc the proto-star would stop collapsing, and and that might be where the process stops. No doubt this happens but as yet I haven't read about it. It would be like a MACHO and could be in part contributing to the dark matter of the galaxies. - failed proto-stars, partially collapsed nebulae - interesting.
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I was just using that for an example. In our solar system most of the gravitational influence is in the center, the sun itself. That doesn't happen to be the case for our galaxy where most of the gravitational influence is spread out in the disk of stars. That disk of stars has a lot more influence on the outer stars than I've heard any scientists giving credit to, to help account for the greater than expected speed of those stars.
 
Robittybob1 said:
Why should it concern me? You don't make that clear.
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The Average density of Sun is not an issue to be concerned about. But I would think you first need to establish the density of dark matter around our solar system. Sense we haven't been able to detect any DM, that might be very hard to do.
 
Scott Myers said:
Density, as far as orbital calculations are concerned, are only important if you can get closer to this super dense core, closer to the center of the mass. The closer you can get, the faster a stable orbit must be, and the stronger the Gravitational force, for lack of better words. When something is denser overall, or less dense overall, matters much since you cannot get any closer than the surface of either object. The overall density then has the greatest effect for potential gravitational influence.
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I was just not very clear on how this applied to DM. Still not. When our sun turns into a red giant it will have much less average density than it does now. I guess a stable orbit within the suns plasma surface would be impossible. But I suspect it might still take some time before our planet would be totally burned up and gone.:D
 
KilljoyKlown said:
The Average density of Sun is not an issue to be concerned about. But I would think you first need to establish the density of dark matter around our solar system. Sense we haven't been able to detect any DM, that might be very hard to do.
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Agreed. Our Density, or should we say distribution, of Dark Matter is compiled where it is needed to account for our descepencies in expected orbital velocities and what we are observing.
 
Scott Myers said:
I think we have pretty much figured out during the course of this topic that the expected curve does take this into account, the cumulative mass within each orbital sphere that is, but still falls short of solving the velocities observed. The example you usually see is the curve predicted for planets, but that is merely a simplistic way of showing the basic logic of the problem we are facing.
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That may be, however, it's not documented or explained very well in any of the science programs on TV. Why do you think that is?
 
KilljoyKlown said:
The Average density of Sun is not an issue to be concerned about. But I would think you first need to establish the density of dark matter around our solar system. Sense we haven't been able to detect any DM, that might be very hard to do.
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It was based on the required gravitational effect. I haven't got my gray-matter around the dark matter problem yet.
 
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