In any given layer of a star, there is a hydrostatic equilibrium between the outward thermal pressure from below and the weight of the material above pressing inward. The isotropic gravitational field compresses the star into the most compact shape possible. A rotating star in hydrostatic equilibrium is an oblate spheroid up to a certain angular velocity. An extreme example of this is the star Vega, which has a rotation period of 12.5 hours and is about 20% fatter at the equator than at the poles because of it. Above that critical velocity, it becomes a Jacobi (scalene) ellipsoid, and at still faster rotation it is no longer ellipsoidal at all but piriform, with yet other shapes beyond that.[1]
If the star has a massive nearby companion object then tidal forces come into play as well, distorting the star into a scalene shape when rotation alone would make it a spheroid. An example of this is Beta Lyrae.
Hydrostatic equilibrium is also important for the intracluster medium, where it restricts the amount of gas that can be present in the core of a cluster of galaxies.
proactol
Genital warts
If the star has a massive nearby companion object then tidal forces come into play as well, distorting the star into a scalene shape when rotation alone would make it a spheroid. An example of this is Beta Lyrae.
Hydrostatic equilibrium is also important for the intracluster medium, where it restricts the amount of gas that can be present in the core of a cluster of galaxies.
proactol
Genital warts
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