Differential rotation

From Differential rotation (Super rotation) occurs when the angular velocity of a rotating body / system is different depending on the latitude of the point or its distance from the axis of rotation, the body is not so turns just as fast. This is not possible with solids.

A differential rotation is always associated with a shear.

Examples

Generally

For example, there are the surfaces of the Sun, Jupiter, and Saturn in differential rotation. The regions close to the equator rotate much faster than those in the region of the poles. Usually, galaxies, accretion disks and protostars also have a differential rotation.

Earth

The differential rotation between Earth's core and mantle is as a result of flows accepted by the geodynamo, which builds the geomagnetic field. This means that the super rotation is probably a consequence and not the cause of the geodynamo.

Our Solar System

An example of differential rotation is the solar system: almost all the mass is in the central body - the sun - and unites the planets revolve (in general, in Kepler orbits ) in nearly circular orbits around it. The Kepler 's laws describe the motion: The closer an object is to the central mass, the faster ( both web speed and angular velocity ), he has to move if he wants to move in a constant / stable web. For these pathways results in:

So with the following:

So it turns out:

The self-rotation of the sun and the gas planets

When the sun and the gas planets, the equatorial regions, a shorter rotation period than the poles.

The cause is probably that it is not to rigid celestial bodies and the angular momentum due to thermal processes is urged in the regions with the largest radius because all matter, faster than the average moves due to thermal motion in the circumferential direction, by the same higher centrifugal force pushes outwards.

The Milky Way

In 1927 the Dutch astronomer Jan Hendrik Oort has shown that our galaxy, the Milky Way, is in differential rotation: the stars near the center have a greater angular velocity than those in the outer regions ( rotation curve, Oort rotation formulas ).

From the Bahngeschwindgkeiten about Newton's law of gravitation to draw conclusions about the mass distribution of a galaxy can be drawn. It turns out that the train speeds not lose weight within a galaxy to the outside, which would suggest due to the distribution of visible matter, in some galaxies soar even slightly. The differences between observed orbital velocities and calculated values ​​ultimately led to the assumption that there must be in addition to the visible yet another form of matter, enter the unobservable dark matter. Another theory tries this difference by a modification of Newton's law of motion to explain (so-called modified Newtonian dynamics).