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3

The argument goes something like this. Hydrostatic equilibrium means that the local pressure gradient is proportional to the local density multiplied by a latitude-dependent local gravity. If the pressure just depends on density and temperature, this means that those quantities will also just depend on latitude and therefore will be constant along an ...


2

From the same Wikipedia page: This means that equatorial regions of a star will have a greater centrifugal force when compared to the pole. The centrifugal force pushes mass away from the axis of rotation, and results in less overall pressure on the gas in the equatorial regions of the star. This will cause the gas in this region to become less dense, and ...


6

The key concept is called Tidal locking. Earth's gravity forced the Moon to rotate in that way during the first few tens of millions of years after the Moon formed and then kept it that way. The wikipedia page describes the mechanism: Consider a pair of co-orbiting objects, A and B. The change in rotation rate necessary to tidally lock body B to the larger ...


7

The question doesn't have a single answer, because the Milky Way's rotation is differential rather than solid-body. This means that stars in the inner part complete their rotation about the center in a shorter period of time than stars at a larger radius. Stars orbiting with a radius of 1 kpc (about 3,000 light years) will take about 30 million years to go ...


4

In general, Milky Way stars that are 13-14 billion old are part of the Galactic halo, and roughly spherical distribution of stars that contains the globular clusters. This part of the Galaxy formed first, and the flattened Galactic disk is more like 10 billion years old. At that point, the disk had formed, and large-scale movements of mass were probably ...


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