# What is Galaxy rotation curve: Definition and 12 Discussions

The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre. It is typically rendered graphically as a plot, and the data observed from each side of a spiral galaxy are generally asymmetric, so that data from each side are averaged to create the curve. A significant discrepancy exists between the experimental curves observed, and a curve derived by applying gravity theory to the matter observed in a galaxy. Theories involving dark matter are the main postulated solutions to account for the variance.The rotational/orbital speeds of galaxies/stars do not follow the rules found in other orbital systems such as stars/planets and planets/moons that have most of their mass at the centre. Stars revolve around their galaxy's centre at equal or increasing speed over a large range of distances. In contrast, the orbital velocities of planets in planetary systems and moons orbiting planets decline with distance according to Kepler’s third law. This reflects the mass distributions within those systems. The mass estimations for galaxies based on the light they emit are far too low to explain the velocity observations.The galaxy rotation problem is the discrepancy between observed galaxy rotation curves and the theoretical prediction, assuming a centrally dominated mass associated with the observed luminous material. When mass profiles of galaxies are calculated from the distribution of stars in spirals and mass-to-light ratios in the stellar disks, they do not match with the masses derived from the observed rotation curves and the law of gravity. A solution to this conundrum is to hypothesize the existence of dark matter and to assume its distribution from the galaxy's center out to its halo.
Though dark matter is by far the most accepted explanation of the rotation problem, other proposals have been offered with varying degrees of success. Of the possible alternatives, one of the most notable is modified newtonian dynamics (MOND), which involves modifying the laws of gravity.

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1. ### I Explanation for Galaxy Rotation Curves

The existence of dark matter was initially proposed to address discrepancies between observed galaxy rotation curves and the expected behavior dictated by our current understanding of gravity. Typically, it's argued that stars at the edges of galaxies rotate faster than expected, leading to...
2. ### I Calculating Time Dilation & Galaxy Rotation Curve

Hello, What I understood from multiple answers on different threads is that the effect of the time dilation is too small to explain the galaxy rotation curve. I was advised to do some calculations in order to see it myself. And this is what I would like to do but I need some help. - What is...
3. ### I Galaxy Rotation Curves and Mass Discrepancy

I apologize for the simple question, but I am trying to understand the Mass Discrepancy-Acceleration Relation and its relationship to ##\mu(x)## (from https://arxiv.org/pdf/astro-ph/0403610.pdf). The mass discrepancy, defined as the ratio of the gradients of the total to baryonic...
4. ### I Galaxy Rotation Curves: Newton's Shell Theorem Impact

I apologize for the simple question, but I have not been able to find the answer. For the inner portion of a galaxy rotation curve (where the outer portion is the part invariant to distance and the inner part is where rotational velocity increases with radius), how much is simply due to...
5. ### Galaxy centre and rotation curve

What is the density of galactic centre? Thus what form of Kepler's law account for the galaxy rotation curve increasing near the galactic centre?
6. ### Question re Galaxy Rotation Curve

The diagram below is from https://en.wikipedia.org/wiki/Galaxy_rotation_curve . I would much appreciate a derivation explaining the shape of the "Expected from visible disk" curve in the diagram. Naively, based on Newtonian mechanics for the orbital velocity of a circular orbit, V = √GM/R ∝...
7. ### Galaxy rotation curve of higher mass galaxy with same size

How would a galaxy rotation curve look if every matter simply had a 6 times larger mass than the visible? (please neglect how that could be) Wouldn't a same size galaxy then reside in a 6 times larger gravitational well so that the spiral arms would still be in the steep part of the well...
8. ### Galaxy Rotation Curve problem -

Hi folks, I'm supposed to derive the func. form of the rotation curve for the outer parts of our galaxy, in the absence of dark matter. Im assuming that I treat this as a linear curve, since in reality, dark matter flattens out the curve, when it should continue following the linear(?)...
9. ### What are the key theories used to predict galaxy rotation curves?

Do any of you know which article(s) are used to do the "expected" rotation curve for galaxies, that always seem to be used to compare with data for calculating the distribution of dark matter? I'm just trying to find which authors have worked out a published result for the theoretical...
10. ### How Does Galaxy Rotation Curve Influence Mass and Luminosity Calculations?

Hi all, this is the problem: Homework Statement A galaxy shows a rotation curve with a given velocity v(r) . r is the distance from the center, c is the speed of light and r_{c} = 1 kpc is constant. I have to find: 1) the mass density profile of the galaxy \rho(r) 2) the total mass M...
11. ### Gravitational Time Dilation and the Galaxy Rotation Curve

Is it possible that the very high concentration of mass at the centers of galaxies is causing a significant enough time dilation to explain a non-negligible part of the rotational curve problem? i.e. time is traveling more slowly in the super-massive, black hole rich cores of galaxies and faster...
12. ### Galaxy rotation curve: Applicability of formula

Homework Statement Derive and plot the rotation curve of a galaxy with logarithmic potential: \Phi(R, z) = \frac{v_0^2}{2}\ln{(R_c^2 + R^2 + q_{\phi}^{-2} z^2)} where R_c = 2 kpc, q_{\phi} = const. and v_o = 200 kms^{-1}. Note that v_c is defined for z = 0 only. Homework Equations...