New measurements of galaxy rotation lean toward modified gravity as an explanation for dark matter

Though dark matter is a central a part of the usual cosmological mannequin, it is not with out its points. There proceed to be nagging mysteries concerning the stuff, not the least of which is the truth that scientists have discovered no direct particle proof of it.

Regardless of quite a few searches, we’ve got but to detect dark matter particles. So some astronomers favor another, comparable to modified Newtonian dynamics (MoND) or modified gravity model. And a brand new research of galactic rotation appears to assist them.

The thought of MoND was impressed by galactic rotation. Many of the seen matter in a galaxy is clustered within the center, so that you’d count on that stars nearer to the middle would have sooner orbital speeds than stars farther away, just like the planets of our solar system. What we observe is that stars in a galaxy all rotate at about the identical pace. The rotation curve is basically flat reasonably than dropping off. The dark matter resolution is that galaxies are surrounded by a halo of invisible matter, however in 1983 Mordehai Milgrom argued that our gravitational mannequin should be improper.

At interstellar distances, the gravitational attraction between stars is basically Newtonian. So reasonably than modifying general relativity, Milgrom proposed modifying Newton’s common regulation of gravity. He argued that reasonably than the pressure of attraction as a pure inverse sq. relation, gravity has a small remnant pull no matter distance. This remnant is just about 10 trillionths of a G, but it surely’s sufficient to clarify galactic rotation curves.

In fact, simply including a small time period to Newton’s gravity signifies that you even have to change Einstein’s equations, as nicely. So MoND has been generalized in numerous methods, comparable to AQUAL, which stands for “a quadradic Lagrangian.” Each AQUAL and the usual LCDM mannequin can clarify noticed galactic rotation curves, however there are some refined variations.

That is the place a latest research is available in. One distinction between AQUAL and LCDM is within the rotation speeds of interior orbit stars vs. outer orbit stars. For LCDM, each must be ruled by the distribution of matter, so the curve must be easy. AQUAL predicts a tiny kink within the curve because of the dynamics of the speculation. It is too small to measure in a single galaxy, however statistically, there must be a small shift between the interior and outer velocity distributions.

So the creator of this paper checked out high-resolution velocity curves of 152 galaxies as noticed within the Spitzer Photometry and Correct Rotation Curves (SPARC) database. He discovered a shift in settlement with AQUAL. The info appears to assist modified gravity over commonplace dark matter cosmology.

The result’s thrilling, but it surely does not conclusively overturn dark matter. The AQUAL mannequin has its personal points, comparable to its disagreement with noticed gravitational lensing by galaxies. However it’s a win for the underdog concept, which has some astronomers cheering “Vive le MoND!”

The analysis is revealed on the arXiv preprint server.