Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Spiral and Disk Galaxies are controlled by single parameter. What and How?

  1. Jun 25, 2010 #1
    This is a significant discovery that something is fundamentally controlling and ordering the properties of spiral and disk gaseous galaxies. Elliptical galaxies have no gas and no star formation.

    The question is not only what but how is the unknown parameter controlling spiral and disk galaxy evolution and properties.

    This appears to me to be a discovery as significant as the Hertzsprung-Russell diagram which led to the formation theory of stars.




  2. jcsd
  3. Jun 26, 2010 #2


    User Avatar
    Science Advisor

    From what I hear batted around by those studying these things, those within the field seem to currently consider AGN feedback to be the primary mechanism that distinguishes spiral behavior from elliptical behavior. Though it's also worth mentioning that galaxies are understood to be incredibly complex beasts, and there are sure to be many other factors at work as well.
  4. Jun 26, 2010 #3
    Feedback can not explain any observation. There are presentations concerning these anomalies that are starting to make jokes about the feedback attempt. (i.e. It seems it may not be physically viable. If it is not that is a triumph for scientific analysis as it important not to parameter fit an incorrect mechanism as it stops progress.)

    Feedback was also used in an attempt to explain the discrepancy between the observed variance of rotational velocity of spiral galaxies with radius vs what the models predicted with dark matter. (The problem is the dark matter models predict the spiral galaxy's rotational velocity should change as 1/radius of the galaxy as one move from the centre of the galaxy to the galaxy's outer radius, particularly as one reaches the centre of the galaxy. Observationally the rotational velocity of the spiral galaxy changes linearly with radius. The models predict galaxy bulges that are too large (this is related to the rotational velocity observation) and the number of satellite galaxies that is predicted is higher than what is observed by a factor of 10. There are other problems.)

    As there are groups of anomalies concerning spiral galaxy & BHs properties and the evolution of those properties with redshift it seems likely there may be a fundamental model explanation for all of the anomalies. i.e. The correct mechanism will explain the entire set and may eliminate other assumed mechanisms which are starting to have trouble. (I will start another thread sometime to elaborate.)

    The logical approach is to look to see if there are other observational anomalies concerning the spiral galaxies, spiral galaxy stars, BH holes, BH and Spiral galaxy property evolution wiht redshift looking for a hint as to what the correct fundamental model might be.
  5. Jun 26, 2010 #4
    I am not sure people will understand why this observation is interesting or why it is placed in a thread that discusses the observational finding that spiral galaxy properties are tightly controlled and there is currently no physical explanation for why spiral galaxy properties are tightly control and interrelated.

    Perhaps a specific example might help to illustrate the severity of the puzzles. Try to explain the observations using standard assumed models.

    Spiral galaxy luminosity for example is tightly related to the galaxy in questions' rotational velocity. (This relationship is called the Tully-Fisher luminosity vs rotational relationship) Also the galaxies mass is tightly related to the galaxies rotational velocity (That relationship is called the Tully-Fisher Baryonic mass to rotational relationship.)

    Now think about what is observed. How could a galaxy's rotational velocity change with time? Galaxies are getting large with higher redshift and those that have most rotational velocity are the most luminous and have the most mass. What model are you assuming (i.e. Physically what are you assuming is happening to the spiral galaxy in question? What is happening to the spiral galaxy to increase its rotational velocity? When you are increasing the rotational velocity of the spiral galaxy how do you keep a close relationship to the galaxy's luminosity?

    The ratio of the BH hole's mass to the ratio of BH hole's Host galaxy get less with redshift by a factor of 7 from z=0 to z=3. Gets less by a factor of 7. Gets less by a factor of 7.

    Either the BH has lost mass which is assumed to be impossible or the galaxies have gained mass or BH mass formation was more efficient at Z=3 than Z=0 in a manner that changes with in a straight line with redshift.

    I am placing this observation in this thread because it concerns an anomaly concerning mass. Specific astronomical objects have more or less gas. Gas is mass.

    This is a public link to the same paper.


  6. Jun 26, 2010 #5


    User Avatar
    Science Advisor

    I don't understand why this would be terribly surprising. Spiral galaxies tend to have lots of interstellar dust, dust which also feeds star formation. The dust itself feeds star formation, and also adds a friction term that would relate to the galaxy's rotational velocity. The existence of a direct relationship between rotational velocity and luminosity, then, is likely to be telling us something interesting about the nature of the gas physics in these galaxies.

    More likely what you're seeing here is a selection effect. It's easier to observe and measure smaller black holes that are nearby. The only ones that we can see at large distances are the ones that are larger. I sincerely doubt that this will turn out to be a real relationship.
  7. Jun 26, 2010 #6
    What friction factor increases the rotational velocity of galaxies? Explain the friction factor. Angular momentum is conserved. There must be a torque to create the increase rotation. Try mergers. The problem however with mergers is in simulations mergers of spiral with spiral creates an elliptical galaxies. The fraction of spiral galaxy to elliptical galaxy stays roughly constant with redshift at 70% spiral and 30% elliptical.

    There are other papers on the same subject. I have not heard anyone proposing that it is do to selection factor.

    Note the host galaxy's mass increases relative to the BH by a factor of 7 from z=3 to z=0. There must be massive amounts of new gas that enters the galaxy and does not increase the mass of the BH, or there must be mergers that increases the mass of the galaxy but not the mass of the BH or the BH must be losing mass to the its host galaxy which we believe is physically not possible.

    As noted above the problem with mergers is simulations show a merger of spiral to spiral creates a elliptical galaxy.

    Note also there is the requirement to provide a physical explanation of Disney et al's discovery that spiral and disk galaxy properties are tightly control by a single mechanism and that mechanism also increases rotational velocity.
  8. Jun 26, 2010 #7


    User Avatar
    Science Advisor

    Generally when a gravitational system loses energy through friction, it collapses inward, which causes it to speed up its rotation.

    Ah, well, that actually makes sense. There are two possibilities that I can see:
    1. Most of the mergers are with smaller galaxies that don't disturb the spiral structure.
    2. Galaxies, if they have a significant amount of interstellar dust remaining, tend to revert to a spiral shape after mergers.

    I suspect the first is the far more likely option of the two.

    Only simulations of mergers with nearly equal-mass galaxies.

    A single parameter is not a single mechanism. The two are different concepts, and probably says more about the dynamics, likely due to baryonic physics combined with AGN feedback, that lead galaxies to one of two potential end fates than anything else.
  9. Jun 26, 2010 #8
    You are thinking about a star not a galaxy. When a rotating cloud that has angular momentum collapses the cloud's rotational energy is conserved and the rotational velocity of the resultant; stars and planets increases.

    For this case the galaxies in question increase in mass is due to the in falling of new gas clouds. (The galaxies increase in mass from z=3 to z=0 by a factor of 7, in relationship to their black holes.). (i.e. The initial cloud that formed the galaxy is the source of the galaxy's angular momentum. Gas clouds do not de facto have angular momentum unless they are part of a rotating spiral galaxy which has angular momentum. There are clusters of stars that formed from gas clouds that did not rotating in regions about our galaxy that do not have angular momentum.)

    The source of the spiral and disk's angular momentum is hypothesized to be torque of two different gas clouds. That mechanism does not explain how spiral galaxies can increase their rotational velocity as they grow. Compare a spiral galaxy to an elliptical galaxy.

    What we would expect is all galaxies should be elliptical. Multiple merger events of spiral galaxies should create elliptical galaxies. Gas clouds and spiral galaxies fall into the spiral galaxy from random angles. The resultant is a group of stars (elliptical galaxy) that has typically no significant net rotation. (i.e. Elliptical galaxies' stars rotate in clockwise and counter clockwise about up to three rotational axises so net sum of the angular momentum cancels.

    Subsequent gas clouds that falls into the galaxy's disk gas cloud heats up the disk gas but does not increase the rotational velocity of the disk. (There is friction which heats up the gas and dissipates the kinetic energy of the in falling gas cloud but no increase in angular momentum. Angular momentum is conserved.) There is hence no increase in rotational velocity.
  10. Jun 26, 2010 #9


    User Avatar
    Science Advisor

    No, it's a general statement. It comes from the fact that a random walk diverges from the zero mean by the square root of the number of steps. So when you produce a gas cloud by starting from a big, diffuse entity that collapses inward, on average you get something with quite a bit of angular momentum and noticeable rotation.

    There's nothing fundamentally different about this situation versus producing a large galaxy through a merger of a large number of small ones: each one will add a random angular momentum that will, in general, not be zero, and not add to zero. All that you need is some friction to transmit the angular momentum from the incoming gas clouds to the rest of the galaxy.

    Of course, the devil is in the details, and it may well be difficult to get the right amount of rotation. But the simple fact of galaxies increasing in apparent angular momentum with mergers doesn't surprise me in the least.

    No, it's a random walk. In the ensemble average the angular momentum may be zero, but individual galaxies will definitely not have zero angular momenta. The difference is that the elliptical galaxy typically has very little dust, which means very little friction, so that you just don't see the angular momentum because the stars aren't forced to line up along the direction of average rotation.
  11. Jun 27, 2010 #10
    I get the impression that the "no significant net rotation" is being misinterpreted, a tub full of moving marbles may not exhibit a preferred rotational axis, but it is hardly sitting still.

    We can observe that dusty spiral galaxy effectively transfers so much rotational motion along the same axis, why wouldn't a less dusty elliptical be more randomized?
  12. Jun 27, 2010 #11
    You comment is not correct. Because you live on a rotating planet, that orbits a star, in a rotating spiral galaxy you assume gas clouds when they collapse will always rotate which is not correct.

    The gas cloud will only rotate if it had initial angular momentum (i.e. It was rotating before the collapse). Angular momentum is conserved.

    What you are describing: A gas cloud that does not have angular momentum suddenly as it collapses develops angular momentum is not physically possible. Just as the water molecules in a glass of water do not suddenly jump out of the glass. i.e. One cannot command all the molecules to change direction or to move about an axis. Think of the trillions of atoms and molecules moving randomly and each individual collision of atom or molecule with atom or molecule. Each collision is from a random direction. The resultant is also random.

    You use the word random in your explanation but do not accept the logical consequences of the word random when applied to trillions of individual gas atoms and molecules. Collapsing gas clouds only rotate when they collapse if they where rotating before collapsing.
  13. Jun 27, 2010 #12

    Jonathan Scott

    User Avatar
    Gold Member

    Next you'll be telling us that bath water doesn't form a vortex above the plug hole.

    You're over-stating this.

    Small irregularities in velocity and momentum at a large radius give rise to amounts of angular momentum which may appear insignificant, but when the same material is reduced to a much smaller radius, it becomes statistically improbable that it does NOT end up spinning.

    Perhaps you're expecting the "randomness" to smooth this out. If you have a larger sample of something random, then it's usually true that the relative deviation from the mean decreases, but it can't simply be assumed to be zero.
  14. Jun 27, 2010 #13


    User Avatar
    Science Advisor

    Well, in a sense. But you missed my point. If you take a collection of atoms in a gas cloud, and completely randomize their trajectories, each will provide a random contribution to the overall angular momentum. I'd have to work out how this goes in three dimensions, but it's basically going to end up that the typical angular momentum of a gas cloud will be some number times the typical angular momentum of a single particle times the square root of the number of particles in the gas cloud.

    So, as long as the gas cloud starts out much bigger than its eventual collapsed size, you are guaranteed to get noticeable rotation. Now, granted, obviously there had to be some average rotation to begin with, but my point here is that before the gas cloud started to collapse, its rotation wouldn't have been noticeable. It's only once it has collapsed that you are left with a significant amount of rotation.
  15. Jun 27, 2010 #14
    Puzzle 1: Spiral galaxies are simple. i.e. All the different galaxy parameters for disk/spiral galaxies are patterned indicating that they are controlled by something. What and How?

    Disney et al finding that spiral galaxies' parameters are tightly controlled by some unknown parameter and or mechanism was not expected and currently has no explanation.

    Puzzle 2: What causes spiral/disk galaxies to form as opposed to elliptical galaxies and visa versa?

    Connected with Disney's finding is the problem of explaining the two different galaxy general galaxy types: disk/spiral and elliptical

    Puzzle 3: Ratio of Disk/Spiral galaxy's BH mass to Host galaxy's mass increases by a factor of 7. Why?

    The finding that the ratio of the spiral/disk galaxy's mass to the ratio of the host's galaxy's Black Hole (BH) increases by a factor of 7 from z=3 to z=0 also does not have an explanation. As I noted above either the host galaxy's BH's mass must be getting less with time which we believe is not possible or the mass of all disk/spiral galaxies must be increasing with time in a manner that does not increase the mass of the host galaxy's BH.

    Puzzle 4: Curious non random angular momentum oddities in the Milky Way. Angular momentum is conserved. What is causing the observed angular momentum change with time?
    If you look into the observations for the Milky Way at detail what is observed is not random. There are puzzling indications of some mechanism that affects rotational velocity. For example is a rotation difference between the thick disk which is older than the thin disk which contains the gas. (The thick disk rotates at a slightly lower speed.) It looks as if something is creating gas in the galaxy and increasing its angular velocity, in the galaxy's disk.

    Puzzle 5: Sun's movement outward in the Galaxy. Is this a one of or are other stars moving outward in the galaxy? See puzzle 4. If stars are moving, next question, are all stars the same? Could some stars move outward and others not?

    Curiously based on an analysis of solar metallicity it has been shown that the sun has moved outward in the Milky Way by a 1000 light years since it was formed. This observation is alleged to be due fortuitous interaction in the original cluster of stars that the sun was formed in. If you remember it was been found that spiral/disk galaxies at high redshift are massive but compact. Some unknown force is causing the spiral/disk galaxy to expand.

    Puzzle 6: Spiral galaxy's rotation anomaly. What is causing that observation? Note all efforts to directly detect dark matter in laboratory experiments have failed. If Shanks' finding of an error in the interpretation of the CMB analysis is correct there is no longer support for the existence of dark matter based on patterns in the CMB.

    As noted based on observations the spiral galaxy's rotational velocity changes linearly with radius. Dark matter simulations predict spiral galaxy's rotational velocity should change as 1/radius of the galaxy decreasing as one reaches the center of the galaxy there by creating a central galaxy bulge that is large than observed.

    Back to thinking about the observations. This comment concerns the two different galaxy types Spiral and Elliptical.

    Collisions of spiral with spiral should create an elliptical galaxy. Observationally however the percentage of spiral to elliptical remains almost constant with redshift (time) at 70% spiral to 30% elliptical.

    Extragalactic Astronomy and Cosmology An Introduction by Peter Schneider


    page 92:


    Last edited by a moderator: May 4, 2017
  16. Jun 27, 2010 #15


    User Avatar
    Science Advisor

    As I've said previously, interactions with the interstellar gas are the most likely explanation for most of these, with AGN feedback primarily affecting the amount of gas within the galaxy (and thus the differentiation between elliptical/spiral galaxies). Getting the baryonic physics correct is absurdly difficult, and it shouldn't be too surprising that many of the subtle details of our simulations don't yet match up with reality.

    And no, Shanks' finding doesn't impact the evidence for dark matter in the CMB.
  17. Jun 27, 2010 #16
    Bath water forms a vortex because the planet rotates.

    The resultant of collapsing gas clouds will not rotate if it did not have initial angular momentum.


  18. Jun 27, 2010 #17
    If there is no net angular momentum of the initial gas cloud there will be no net angular momentum after collapse.

    You are appealing to complexity (i.e. The vast number of particles and there motions.) to create net angular momentum which is not possible. Angular momentum is conserved.


    Just as water does not jump out of glass as the water molecules move randomly and the after collisions continue to move randomly.
  19. Jun 27, 2010 #18


    User Avatar
    Science Advisor

    Nope. It's got nothing to do with that. The coriolis force from the Earth's rotation is insignificant on those scales. It is significant for hurricanes (and other large weather systems) due to their size. It is significant for tornadoes due to their high wind speeds. But it isn't significant for things like toilets and bathtubs.

    And gas clouds will, in general, not have zero angular momentum, even with fully-randomized initial conditions.
  20. Jun 27, 2010 #19

    The problem is that simulations produce what is observed for an elliptical galaxy. A complicate object that has multiple rotational axises and that has stars that rotating in multiple directions about galaxy. The point is galactic collisions are at random angles and the galaxies that collide can have different rotational directions.

    That fact that observationally spiral galaxies multiple parameters are tightly controlled by some "parameter" and or mechanism was not expected and has no explanation.


    If Shanks' finding is correct the CMB data cannot be used to support the existence of Dark Matter. The first peak in the CMB data which is alleges to show dark matter exists changes by 30%. Where previously what was predicted agreed with the measurements by better than 1%. Shanks et al used a distance object to calibrate the CMB data analysis. The authors of the original analysis used Jupiter which gave them the answer they wanted. It should be noted the CMB authors knew the answer they wanted (i.e. What the Dark Matter theoretical first CMB peak should be) before did their analysis.

    What we have is an unexplained rotational anomaly of spiral galaxies. As noted above the specific variation of rotational velocity with distance from the center of the spiral galaxy changes linearly while the Dark Matter simulations show it should change at 1/radius of the spiral galaxy which will in addition to creating a different rotational variance with distance from the center of the spiral galaxy will based on simulations create a galaxy bulge that is much larger than observed.

    As other authors have noted the finding of massive amounts of gas in clusters removes the need for dark matter to explain cluster motions which has the first indication that "dark matter" was needed by the theory.

    The point is Dark Matter does not explain the observations. "Dark Matter" is a place holder for what ever mechanism is causing what is observed. New analysis and data refutes the existence of Dark Matter from multiple logical bases.
  21. Jun 27, 2010 #20


    User Avatar
    Science Advisor

    So? Elliptical galaxies are quite a bit simpler.

    There's no possibility of changing the first peak by 30%. Anyway, it's the ratio between the even and odd peaks that is important, not the amplitude of the first peak.

    That's nonsense. Jupiter has a vastly smaller angular size than the beam, so its size had very little impact on the beam shape. And by the way, the WMAP team also made use of Mars, Saturn, Uranus, Neptune, and five celestial sources. They also took into account seasonal variation and the angular size of their sources in the calculations. You can read the full paper in detail here:

    The main point here is that Jupiter is by far the brightest source in the sky at the wavelengths WMAP is looking at. So it would be foolish not to use it to calibrate the instrument. Only using much lower signal-to-noise sources like distant quasars is more likely to lead to an incorrect result.

    Then there's also the point that if the WMAP result were off by 30%, ground and balloon-based measurements of the CMB would be completely inconsistent with WMAP. So no, there is no possibility of the WMAP beam shape being off by enough to change the first peak by 30%.

    Far more likely to be an issue with the simulations than fundamental physics. Spiral galaxies are horribly complex beasts.

    Uh, what? Look at the Bullet Cluster. The mass is not in the same location as the cluster gas, ergo the cluster gas isn't the explanation.

    Sorry, but in every single observation where the systematic errors are well-controlled, dark matter provides an excellent fit to the data. It is only when we start moving into areas where the systematic errors aren't as well-understood (such as within spiral galaxies) that we start to have problems.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook