The velocity dispersion of gas within galaxies is typically 30-40 km/s. Stars are born in gas clouds. But later on, their orbital velocities reach several hundreds of km/s. How is this possible? Where and how do the stars gain their angular momentum and their final orbital velocity?
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4$\begingroup$ Velocity dispersion is not the orbital velocity of the gas, is it?\ $\endgroup$– AtmosphericPrisonEscapeDec 20, 2022 at 20:41
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The velocity dispersion of giant molecular clouds in the vicinity of the Sun might be 30-40 km/s (this sounds too large to me actually), but their orbital speeds are of order 220 km/s, like the Sun.
The velocity dispersion is the spread around an average value. The orbital speeds of stars are similar to the clouds from which they were born.
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2$\begingroup$ Thanks, you're right. I misunderstood that the frame of reference of the velocity 'dispersion' of gas is not the entire galaxy but the LSR local standard of rest that needs to be added or subtracted depending on the direction of motion. $\endgroup$ Dec 21, 2022 at 12:38