h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Joanna

You may want to add a bit on the evolution of Binary Systems. You can get silly situations where the two stars are physically close. What can then happen is the higher mass star evolves more quickly and may turn into a red giant, depends on mass obviously. In this case the atmosphere may expand to fill the Roche Lobe material falls onto the companion. The Red Giant evetually forms into a white dwarf and the companion has now gained mass altering it's evolution. The companion turns into a red giant and he process is reversed with the white dwarf gaining mass from the red giant. An accretion disk forms and the material falling onto the white dwarf becomes super heated. As it falls onto the surface the stellar material 'explodes'. This we see as recurrent Novae.

If one star is big enough it goes supernovae and leaves a black hole. The other star can evolve into a red giant, exceed it's roche lobes and material falling into the black hole forms an accretion disk. This is the primary detection mechanism for Black Holes, stellar mass companions, non light emitting with high gamma and X-Ray output (due to the accretion disk).

A third scenario involves material falling onto a neutron star. This can trigger Type IA supernovae as the neutron stars mass becomes great enough to form a black hole.

You also have the wierd case of two stellar cores sharing a common atmosphere.

Dave "love them binaries" Barlow

Thanks for pointing that out to me... I can't do anything about it now since this entry's been edited, its out of my hands... Perhaps when it gets reviewed that stuff will be added