A question about Binary star systems and novae

[Sothis]

Lets, for the sake of argument, say that two stars of roughly equal mass and density form a binary star system, and swing around each other like a pair of bolos, 1 AU (93 million miles) apart. Lets also say that star A has enough hydrogen to burn for 10 billion years, and star B for a further 500'000 years.

Star A exhausts it's hydrogen and starts to expand as it undergoes a nova. If I understand things correctly (and I probably don't) the force of gravity between the two stars will now be out of sync, so the orbit of star B will change. Only I can't remember if the process of a nova actually reducesa star's gravitational pull or not (something to do with it's density).

Anyway, eventually, star B, after looping in an increasingly eccentric orbit around the ballooning star A, swings too close and is engulfed.

What happens? Star B still has hundreds of thousands of years worth of hydrogen left to fuse into helium, yet star A is now fusing helium into carbon- will the influx of hydrogen be enough to somehow stablise star A, or is too far gone?

I apologise if I've just mauled basic scientific principles about gravity, mass and density, but science was never my chosen field.

[SirNitram]

That'd make star A a sodding massive Red Giant and star B a tiny Blue star.

[Zoink]

I think you mixed up your stars, you said star A has 10 billion years of fuel left... but its the one going supernova.

So let's say:

Star A: Nova
Star B: Still burning.

Star A will expand to a red giant, keeping a similar orbit (its still the same mass), then nova, leaving a neutron star (or possibly a pulsar or black hole). The neutron star will have less mass, and the orbit will probably increase in size and become more eccentric.

If the stars are close enough, Star B might begin shedding material that accumulates on the neutron star, which will eventually shed the material in a supernova. This will occur periodically, and is known as a type B supernova (I believe).

If the two stars collide, its depends on the size of the size of the stars. I have a Scientific American issue on this very thing. A small dense star hitting a sun-like star would shred the sun-like star to bits, leaving the dense star relatively intact. It might even cause a nova.... The magazine has the different combinations of collisions, giving the probably outcome.... I won't be posting for a few days so I can't get you the info.... perhaps someone else has that issue?

[Zoink]

Here you go:

A white dwarf punching through the sun, I suppose a neutron star would be similar:

Kaboom!

[Einhander Sn0m4n]

Here you go:

A white dwarf punching through the sun, I suppose a neutron star would be similar:

Kaboom!

I would really hate to be anywhere near that point in spacetime....

[SyntaxVorlon]

Whoa.

Well at 1 AU appart the smaller star would orbit the larger one, the fact that one was a red giant would simply mean that it would orbit inside the other's atmosphere. It would probably look like the image under that Kaboom link, with just the bulge in the sun, not the white dwarf.
When A goes nova, lots of stuff start to happen, roughly half of the mass of A is gone, the other half is packed into a dense white dwarf, a quark star, or neutronium. This means that the smaller core remnant of A starts to fall into B or the two fly away from eachother. This depends on the strength of the nova, the ratio of mass between core remnant A and star B, etc.