Galaxy rotation curve: Applicability of formula

In summary, you can derive and plot the rotation curve of a galaxy with logarithmic potential using the equation v_c^2 = -2 \Phi(R, z), where R_c = 2 kpc, q_{\phi} = const. and v_o = 200 kms^{-1}. This equation holds for any gravitational potential, including the logarithmic potential given in the problem.
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Homework Statement


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


Homework Equations


[tex]v_c^2 = -2 \Phi(R, z)[/tex]



The Attempt at a Solution


I'm just wondering if the above equation for circular velocity is applicable in this case. All signs point to yes, but I'm just worried about additional criteria that I may be overlooking.
 
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Hello, thank you for your question. Yes, the above equation for circular velocity is applicable in this case. The circular velocity is defined as the velocity of an object moving in a circular path, and it is directly related to the gravitational potential of the galaxy. In this case, the logarithmic potential describes the gravitational potential of the galaxy, and the circular velocity can be derived from it using the equation v_c^2 = -2 \Phi(R, z). This equation holds for any gravitational potential, including the logarithmic potential given in the problem. Therefore, you can use this equation to derive and plot the rotation curve of the galaxy with logarithmic potential.
 

1. What is a galaxy rotation curve?

A galaxy rotation curve is a graph that shows the speed at which stars and other celestial objects rotate around the center of a galaxy, as a function of their distance from the center.

2. How is the formula for a galaxy rotation curve applicable?

The formula for a galaxy rotation curve, also known as the Keplerian velocity formula, is applicable to spiral galaxies with a single, dominant mass concentration at their center, such as the Milky Way. It describes the relationship between the velocity of an object in circular orbit and its distance from the center of mass.

3. What factors can affect the accuracy of the galaxy rotation curve formula?

The accuracy of the formula can be affected by the presence of multiple mass concentrations, such as a large central bulge or spiral arms, in a galaxy. Additionally, the formula assumes a spherical and stationary mass distribution, which may not always be the case.

4. How do scientists use galaxy rotation curves to study dark matter?

By observing the rotation curves of galaxies, scientists can determine the amount of mass present within the visible portion of the galaxy. If the observed mass is not enough to explain the observed rotation curve, it is believed that the missing mass must be made up of dark matter, which does not interact with light.

5. Are there any alternative formulas for galaxy rotation curves?

Yes, there are alternative formulas that have been proposed to better account for the effects of multiple mass concentrations or non-spherical mass distributions in a galaxy. However, the Keplerian velocity formula remains a useful and widely used tool in studying galaxy rotation curves.

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