Most of the visible matter in a galaxy is clustered in the middle, so you d expect that stars closer to the center would have quicker orbital speeds than stars farther away, comparable to the planets of our solar system. The dark matter option is that galaxies are surrounded by a halo of unnoticeable matter, however in 1983 Mordehai Milgrom argued that our gravitational design needs to be wrong.
Rotation curve of the common spiral galaxy M 33 (blue and yellow points with errorbars) and the predicted one from circulation of the visible matter (white line). The disparity between the 2 curves is represented by adding a dark matter halo surrounding the galaxy. Credit: Public domain/ Wikipedia
Rather than modifying general relativity, Milgrom proposed customizing Newtons Universal Law of Gravity. This remnant is only about 10 trillionths of a gee, however its sufficient to discuss galactic rotation curves.
Dark matter is a main part of the standard cosmological model, its not without its issues. In spite of many searches, we have yet to discover dark matter particles.
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Dark matter is a central part of the basic cosmological model, its not without its concerns. Regardless of various searches, we have yet to spot dark matter particles. The dark matter solution is that galaxies are surrounded by a halo of undetectable matter, however in 1983 Mordehai Milgrom argued that our gravitational design should be wrong.
The inconsistency in between the 2 curves is accounted for by including a dark matter halo surrounding the galaxy. The information appears to support modified gravity over basic dark matter cosmology.
Naturally, just including a little term to Newtons gravity means that you likewise have to customize Einsteins equations also. MoND has actually been generalized in different methods, such as AQUAL, which stands for A Quadradic Lagrangian. Both AQUAL and the standard LCDM design can describe observed galactic rotation curves, however there are some subtle distinctions.
Determined shift between inner and external stellar motions. Credit: Kyu-Hyun Chae
This is where a recent study can be found in. One difference in between AQUAL and LCDM remains in the rotation speeds of inner orbit stars vs external orbit stars. For LCDM, both should be governed by the distribution of matter, so the curve needs to be smooth. AQUAL forecasts a small kink in the curve due to the characteristics of the theory. Its too small to determine in a single galaxy, but statistically, there ought to be a little shift between the inner and outer velocity circulations. So the author of this paper looked at high-resolution velocity curves of 152 galaxies as observed in the Spitzer Photometry and Accurate Rotation Curves (SPARC) database. He found a shift in arrangement with AQUAL. The information appears to support modified gravity over basic dark matter cosmology.
The outcome is amazing, but it does not conclusively reverse dark matter. Thye AQUAL design has its own problems, such as its difference with observed gravitational lensing by galaxies. It is a win for the underdog theory, which has some astronomers cheering “Vive le MoND!”
Referral: Chae, Kyu-Hyun. “Distinguishing Dark Matter, Modified Gravity, and Modified Inertia with the Inner and Outer Parts of Galactic Rotation Curves.” The Astrophysical Journal 941.1 (2022 ): 55.
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