2. Describe the motions of stars in elliptical galaxies. How do the motions of t

Question

2. Describe the motions of stars in elliptical galaxies. How do the motions of the individual stars affect the shapes of the absorption lines in the spectrum of the entire galaxy? How does the mass of an elliptical galaxy affect the speed of the stars. How, then, do we measure the masses of elliptical galaxies?

3. Make a table listing the differences between the shapes, stellar populations, rotation rates, and amounts of gas and dust of elliptical and spiral galaxies. In the same table, compare their ranges of masses and luminosities.

Explanation / Answer

The motion of starts are predominantly radial in elliptical galaxies(unlike those in spiral galaxies where it is mostly rotational). The orbits of the stars are random and often very elongated leading to the shape of the galaxy. This is determined by the speed of the stars in each direction and Because the random orbits of stars, the galaxy appears dimmer than spiral galaxies. Hence the absorption lines are wider and emission lines weaker.

The width of the absorption lines from all the stars blended together is used to measure the mass of the elliptical galaxies.this width is dependent on the velocity distribution of stars(velocity dispersion). So this way as the mass is determined by the velocity distribution, the mass of the galaxy influences the velocity distribution.The elliptical galaxies mass=k*(vel dispersion)^2*(distance the stars are from the galaxy centre) where k is a factor that depends on the shape of the galaxy and the angle is from earth.

Now if the masses of the galaxy is to be measured then distance to the galaxy is to be known. Thus linear distance from the galaxy=(2p*(distance to the galaxy)*angular distance in degrees)/360 deg

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