Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 31/08/2007 15:57:11

Title: Binary, Trinary...sometimes even four ...and then more !..stars!!
Post by: neilep on 31/08/2007 15:57:11

Dear Solar Cells,

This is our sun...

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Nice isn't it ?..notice how warm inviting and alone it is ?


Our sun is in the minority...most stars have a companion star....sometimes even two..occasionally even four or five...................our nearest stellar neighbour for instance consists of a three star system Apha Centauri A, B & C (C is also known as Proxima Centauri)

My question are...how come most star systems comprise of more than one ?..and adversely, how come are the minority just singular ?

Title: Binary, Trinary...sometimes even four ...and then more !..stars!!
Post by: Soul Surfer on 31/08/2007 18:31:10

The answer is because of the angular momentum in the cloud from which the stars formed.

Because of the large scale turbulence of the clouds from which the stars form there is always some residual angular momentum in a cloud that is slowly collapsing and trying to form a star. This causes the cloud to rotate slowly.  As the cloud contracts, this rotation gets faster because the angular momentum is always conserved like energy.  The contraction of a cloud to form a star is very large  so even very slow initial rotations can become very fast and cause the cloud to break up as it contracts this causes separate multiple stars to form.  Stars that form on their own have a relatively small amount of angular momentum but probably form planetary systems to shed excess angular momentum.  If the planets were all added to the sun together with their angular momenta it would cause the sun to rotate so fast it would become unstable.

Title: Binary, Trinary...sometimes even four ...and then more !..stars!!
Post by: lyner on 02/09/2007 23:20:18

Quote

If the planets were all added to the sun together with their angular momenta it would cause the sun to rotate so fast it would become unstable.

Is that really true?  Well I never!
I suppose that, as Moment of inertia is mass times radius squared, the angular momentum  of a distant planet, although small, would be high because of the vast distance squared.  The Sun's mass is huge but it's radius is pretty small and it's not spinning particularly fast.
You must be right.
Well, there you go.