Velocity dispersion

The velocity dispersion is a statistical measure of the distribution of residual velocities of particles towards a bonded system. In astronomy, the velocity dispersion is used to characterize galaxies: spiral galaxies have a small dispersion of 10 to 30 km / s, elliptical galaxies, a dispersion to 400 km / s

Calculation

In the calculation it is assumed that the spectrum of the galaxy can be determined by the spectrum of a single star, provided that the luminosity -weighted average of the whole galaxy is considered. In addition, the distribution of the velocities along the line of sight to a Gaussian distribution should follow. Then the spectrum of each star is displaced so far, to the absorption lines coincide with those of the galaxy. From the radial velocity of the single star can be concluded that of the galaxy. The spectrum of the single star is convolved with a Gaussian function of width. The value of for the best match yields the velocity dispersion.

Importance in astronomy

From the velocity dispersion of stars in the center of the Milky Way can be concluded that the existence and mass of the central black hole. The relatively high rotational speed in the outer spiral arms with small dispersion provides an indication of dark matter.

Swell

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