ATRONOMY – GALACTIC ATRONOMY (30) CALCULATOR
Stellar Velocity Dispersion
A precise tool.
What is the Stellar Velocity Dispersion & How does it work?
Stellar velocity dispersion (Ο) quantifies the random motions of stars within a galaxy and is a key observable for probing the galaxyβs gravitational potential. In massive elliptical galaxies, Ο typically ranges from 100 to 300 km/s, reflecting the depth of the potential well created by the combined mass of stars, gas, and dark matter.
The virial theorem links Ο to the total mass (M) and characteristic size (often the effective radius Rβ) of a galaxy. Assuming the galaxy is approximately spherical and in dynamical equilibrium, the relation can be expressed as ΟΒ² β GΒ·M/(kΒ·Rβ), where G is the gravitational constant and k is a structural constant of order unity (commonly taken as 5 for elliptical systems).
By measuring Ο and Rβ, astronomers can infer the dynamical mass of a galaxy, compare it with the luminous (stellar) mass, and thus estimate the darkβmatter fraction. This method underpins many scaling relations such as the FaberβJackson relation and the Fundamental Plane of earlyβtype galaxies.
\sigma = \sqrt{\frac{G\,M}{5\,R_{e}}}
\sigma = stellar velocity dispersion (km/s)
Parameters
Result
β
Frequently Asked Questions
What is stellar velocity dispersion?
Stellar velocity dispersion measures the random motions of stars within a galaxy, reflecting its gravitational potential.
How does stellar velocity dispersion relate to a galaxy's mass?
According to the virial theorem, stellar velocity dispersion is linked to the total mass and size of the galaxy.
What range do stellar velocities typically have in massive elliptical galaxies?
Stellar velocities in massive elliptical galaxies usually range from 100 to 300 km/s.
Why is stellar velocity dispersion important for astronomers?
It helps probe the galaxy's gravitational potential and infer its mass distribution, including dark matter.
Can stellar velocity dispersion be used to determine a galaxy's age?
While it provides insights into a galaxy's structure and dynamics, direct determination of age requires additional data.
What is the effective radius (Rβ) in the context of galaxies?
The effective radius is the radius within which half of the light from the galaxy is emitted, often used as a characteristic size.
How does stellar velocity dispersion differ from rotational velocity?
Stellar velocity dispersion measures random motions, while rotational velocity refers to ordered motion around the galaxy's center.
Results are for informational purposes only and do not constitute professional advice.