Flat Rotation Curve Astronomy Question

In summary, the conversation discusses a problem involving a spiral galaxy with a "flat" rotation curve and the derivation of the general relation for the orbital period of stars in the galactic disc. The question also asks for the calculation of the orbital period for a star and a hydrogen cloud at specific distances from the galactic centre.
  • #1
ktramsay
1
0
You have to show your attempts at answering the question, this is a forum policy. Also, please use the template. The only reason your post is not deleted is that you already got some help.
I've been struggling with part (a) of this question. I'm not quite sure what the relation is. Any help is greatly appreciated! Thanks!

Consider a spiral galaxy with a “flat” rotation curve beyond the central 2 kpc.

a. Derive the general relation giving the orbital period, P, of a star (or other object) in the disc orbiting the centre of the galaxy, as a function of the radius, R (>2kpc), from the galactic centre.

b. If stars in the flat part of the rotation curve are orbiting at 250km/s, calculate the orbital period, P in years, for a star at 8kpc from the galactic centre and a hydrogen cloud at 30kpc.
 
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  • #2
Well, what does the 'flat' rotation curve mean? How fast are the stars moving? Given how fast they are moving, how long will it take them to complete an orbit of radius R?
 

FAQ: Flat Rotation Curve Astronomy Question

1. What is a flat rotation curve in astronomy?

A flat rotation curve refers to the observed constant speed at which stars and gas move around the center of a galaxy, regardless of their distance from the center. In other words, the outer parts of a galaxy do not rotate significantly slower than the inner parts.

2. Why is a flat rotation curve significant in astronomy?

A flat rotation curve is significant because it challenges the predictions of Newtonian physics, which would suggest that objects farther from the center should rotate slower. This has led to the proposal of dark matter as a possible explanation for the observed flat rotation curves.

3. How is a flat rotation curve measured?

A flat rotation curve is typically measured by observing the velocity of objects, such as stars or gas clouds, at different distances from the center of a galaxy. This can be done using spectroscopic techniques, which analyze the light emitted by these objects to determine their velocity.

4. What is the current understanding of the cause of a flat rotation curve?

The most widely accepted explanation for flat rotation curves is the presence of dark matter in galaxies. This invisible matter has a gravitational effect on the observed objects, causing them to move at a constant speed despite their distance from the center.

5. Are flat rotation curves observed in all galaxies?

No, flat rotation curves are not observed in all galaxies. In fact, galaxies with low masses or low levels of star formation tend to have steeper rotation curves, which align more closely with the predictions of Newtonian physics. This further supports the idea that dark matter is responsible for the observed flat rotation curves in larger galaxies.

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