<p>The velocity <em>dispersion</em> 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.</p>
<p>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.</p>

CC BY-SA 4.0
2022-12-21T12:38:07.003Z
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.
Reggie Grünenberg
CC BY-SA 4.0
2022-12-20T23:28:32.740Z
2022-12-20T23:28:32.740Z
ProfRob
<p>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?</p>

CC BY-SA 4.0
2022-12-20T20:41:43.110Z
Velocity dispersion is not the orbital velocity of the gas, is it?\
AtmosphericPrisonEscape
<galactic-dynamics><galactic-evolution>
Why do stars orbit much faster than gas in galaxies?
Reggie Grünenberg
# Why do stars orbit much faster than gas in galaxies?

(Asked by: username_0 on 2022-12-20)

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?

**Tags:** galactic-dynamics, galactic-evolution
> **Comments:**
> **username_1**: Velocity dispersion is not the orbital velocity of the gas, is it?\  

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## 1 answers

### Answer by username_2 on 2022-12-20. Score: 5 | Accepted answer

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.

> **Comments:**
> **username_0**: 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.  

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