Historically, galactic rotation curves have suggested that galaxies are surrounded by a vast amount of invisible matter, otherwise known as a dark matter halo. A few weeks ago, a team of astrophysicists published a result that completely contradicts these halo models and could even change the popular understanding of dark matter. The team found that galactic rotation curves can be calculated explicitly from a simple equation that only depends on the amount of visible matter in the galaxy. The exact implications of this finding are still unclear, but the authors do suggest a few possibilities.
For almost a century, galactic rotation curves have served as robust evidence for the existence of dark matter. A rotation curve is simply the radial velocity of the stars, dust, and gas that make up a galaxy plotted as a function of their distance from the galaxy’s center. Based on the gravitational pull of matter, one would expect that stars closest to the center of the galaxy would move faster than the stars near the galaxy's outer edge. However, in most galaxies, inner and outer stars move at roughly the same velocity. There is some additional gravitational pull on the outer stars that isn’t fully described by the amount of visible matter in a galaxy. For ages, most scientists have interpreted this result to mean that galaxies are surrounded by a halo of invisible dark matter. Image obtained under Creative Commons License. Credit: Gemini Observatory)
A galactic rotation curve is the radial velocity of the stars, dust, and gas that make up a galaxy plotted as a function of their distance from the galaxy’s center. Based on visible matter alone, one would expect that stars closest to the center of the galaxy would move faster than the stars near the galaxy’s outer edge (dashed line). However, in most galaxies inner and outer stars move at roughly the same velocity (solid line). There is some additional gravitational pull on the outer stars that isn’t fully described by the amount of visible matter in a galaxy. Most scientists have interpreted these rotation curves to mean that galaxies are surrounded by a halo of invisible dark matter. Image obtained under Creative Commons License. Credit: Gemini Observatory
At first glance, the group’s result suggests one could successfully develop a model of galactic rotation curves by modifying gravity, rather than adding in dark matter. However, astrophysicists have made several other observations of the universe that imply modifying gravity isn’t the best way to successfully describe nature. Alternatively, this result could imply a surprising coupling between regular and dark matter, making the two types of matter more correlated than expected. If this scenario were the case, the next step would be to try and probe this coupling in other dark matter experiments.
There is a great deal of excitement surrounding the announcement. It is rare in science to find such a simple equation, with no adjustable parameters that describe observed data. The finding also appears to apply to all spiral and irregular galaxies, regardless of shape or size. Such an elegant and universal relationship suggests a new discovery could be just around the corner.
Acknowledgements: Many thanks to Emma Tolley, a PhD graduate student in Physics. Emma is a member of the Harvard ATLAS group, and is currently searching for dark matter signatures at the LHC.
Managing Correspondent: Karri DiPetrillo
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3 thoughts on “Galactic Rotation Curves Revisited: A Surprise For Dark Matter

  1. Superfluid dark matter fills ’empty’ space, strongly interacts with and is displaced by matter.

    ‘The Milky Way’s dark matter halo appears to be lopsided’
    http://arxiv.org/abs/0903.3802

    “the emerging picture of the dark matter halo of the Milky Way is dominantly lopsided in nature.”

    The Milky Way’s halo is not a clump of dark matter traveling along with the Milky Way. The Milky Way’s halo is lopsided due to the matter in the Milky Way moving through and displacing the superfluid dark matter, analogous to a submarine moving through and displacing the water.

    There is evidence of the superfluid dark matter every time a double slit experiment is performed, it’s what waves.

    What ripples when galaxy clusters collide is what waves in a double slit experiment, the superfluid dark matter which fills ’empty’ space.

    Suprefluid dark matter displaced by matter relates general relativity and quantum mechanics.

  2. I find a consistency for rotation curves with disk shapes in calculations. Simply put the distribution of mass in the disk is consistent with a disk. I calculated the mass inside a series of concentric rings. Subtracting the mass inside a given ring from the total minus outer rings if any gives the mass of a given ring. Calculate the area of that ring and divide the mass of that ring by that area. That gives the mass of the rings per unit area. That shows the mass per unit area in the range of the flat rotation curve to be distributed as would be expected for a disk. One can model idealizations of disks and find that the smaller the central bulge mass relative to the mass of the disk finds expected rotation curve that slopes up (this is what we find in low surface brightness galaxies, small bulge and up slope rotation curve in the disk), and as the relative mass of the bulge increases the rotation curve slopes down to where, in a structure with a bulge and disk we get a horizotal slope, and in a structure like the solar system, with most mass in the center and little in the “disk” the rotation curve slopes down to a Keplerian curve. This is counter to any model of any significant mass in a “halo” outside (above and below) of the disk. In fact modeling a “roughly spherical” mass of uniform density will show an up slope in rotation calculations from the center to the periphery steeper than for a disk with little bulge. That the mass is distributed in a disk shape, even though we cant see it, is counter to the non interacting matter model of the mass we can’t see. The mass is not consistent with dust or gas broadly distributed in the disk. We would detect that. Its distribution is not consistent with massive cold halo objects. Because there is no massive halo. The rotation curves are not consistent with that. But it is consistent with cold massive non stellar objects in the disk. Probably a lot of sub stellar super gas giants. I’ll coin the term Super Jovians. I think that any reasonable analysis of the calculation schema as illustrated above supports that conclusion. No dark non baryonic matter. No modification of Newtonian dynamics. Just a lot of plain old matter in a lot of superjovians.

    1. I get a similar result for galaxy rotation curves for different types of galaxy with or without prominent central bulges. This is compatible with the original paper by Vera Rubin (Rubin, V. (1983). ‘The Rotation of Spiral Galaxies.’ Science, New Series, vol. 220, No. 4604, pp. 1339-1344. Published by: American Association for the Advancement of Science). In my model I integrate the contribution to the gravitational attraction from each section of the galactic disk to give the total contribution at any given point on a set radius. It is unpublished since so far editors have argued against its validity on the basis of not conforming to the standard CDM model.

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