Gravitational disks vs. spheres?
It seems that close in to the source of a large gravitational body, that slave objects will likely form into a disk around it, but much further out, it forms a sphere instead. For example, the planets of the solar system form a disk around the Sun, but much further out around the Oort cloud they form a spherical...
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answers:
Ronald 7 say: The Oort cloud is actually shaped like a Globe with an Equatorial band of swarming long period comets
The Kuiper belt inside it is more of a Torus shape
Billions of years ago our Solar System was a massive cloud of Dust, Ice and Gas
It was sent spinning from an outside force, maybe a close passing Star or more likely a nearby Supernova
The Supernova would have also seeded the primeval cloud with the known Elements
The spin made the cloud collapse toward the centre until the centre became massive enough to bring forth Nuclear Fusion and the Sun
The Solar wind cleared the dust ice and gas to the farthest reaches of the forming Solar system
Closer to the Sun the rocky planets were formed and farther the gas and ice giants
Further out the Sun's gravity becomes so weak it can not hold such small objects, not able to form their own independent gravity, to the Sun's Equatorial belt
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Jeffrey K say: It is due to rotation. Dust around a star and stars in a galaxy orbit a central mass. The centrifical force causes a buldging near the equator and a flattened pancake shape. This even occurs to a very small degree for the earth itself.
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Colly Rodrez say: SPHERES ARE BOOBS!!! THEIR ANOTHER WORD FOR BOOBS HAHAHA
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CarolOklaNola say: Yes there are Any thing with sufficient mass will be spherical because of the laws of gravity and the ideal and combined gas laws along with conservation of momentum, mass and energy.. The forces if gravity and pressure do not have to be equal A sphere is the most energy efficient shape. It contains the maximum volume possible in the smallest surface areas area possible.
The dwarf planet Haumea is in hydrostatic equilibrium, but it is ellipsoidal, not spherical , because it has insufficient mass.
The Hill sphere, the sphere of gravitational influence of a planet is spherical if it has enough mass.
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az_lender say: A rotating spherical blob of stuff that is not totally stuck together will evolve into a disk just because of centrifugal force.
Oort cloud objects may have been captured from other stars, see Levison et al. in Science magazine, July 2010. So the Oort cloud objects were probably never part of the "original" rotating sphere that became a disk.
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Raymond say: Yes and no.
When a large number of distinct objects orbit a common central mass, there will tend to be random collisions among these objects. Every time, some orbital energy is transferred between the two colliding bodies. Although each individual collision is random, the long term trend will be a smooth distribution of the orbiting energy, both in forming a favoured orbital plane AND in reducing the eccentricity of the individual orbits (orbits get to become "more circular")
The faster the orbital speed (i.e., the closer to the central mass) the faster the redistribution of energy.
In the case of the Solar system (and I suspect, any planetary system and even for major planets' satellite systems), the Sun itself was formed by the in-falling matter from the accretion "disk", so that the central body ends up with a rotation in the same direction and with its equatorial plane in the same plane as that of the accretion disk.
Close to the Sun, most of the "stuff" orbits in this preferred plane.
Way out, the distribution is still spherical.
Half-way is... half-way (the Kuiper belt is less planar than the inner planets, but slightly more planar than the Oort cloud).
Old spiral galaxies are somewhat flat.
Then they collide with each other (like Andromeda and us, in 3 billion years or so), thus randomizing the orbits of the stars (a few get ejected, a few get swallowed by the central black holes), and you end up with an elliptical galaxy. With time, this "new" elliptical galaxy will lose its randomness, a preferred plane will appear and it becomes an "old" spiral galaxy, getting flatter by the eon.
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