Will Alpha Centauri A eventually collide with Alpha Centauri B?

Question

The two orbit one another elliptically (e=0.52), approaching as close as 11.2 astronomical units (1.669 billion kilometers or 1.04 billion miles: roughly the distance from the Sun to Saturn) and receding to 35.6 AU (5.9 billion km: approximately the distance from the Sun to Pluto), with a period of just under 80 years. (Wikipedia.com)

Answer 1

They might actually. They will both enter their giant stages in about a few billion years. A will become a red giant first. It will be so big then it will cause drag as B moves through the matter it is expelling and the system will loose kinetic energy. Gradually the stars will then get closer. Eventually A will be a white dwarf but now B will be entering its giant phase and cause more drag. It will be so big and so close to A that it might dump matter onto it. Every now and then A might go nova (not supernova) as that matter from B ignites and is blasted off. Eventually B will be a white dwarf too and now they are both densly packed and exotic materials that cause relativistic effects: two white dwarfs orbiting each other will radiate off gravity waves bringing them closer and closer. Eventually they will merge and their combined mass will exceed the Chandrasekhar limit. And they annihilate each other in a Type I supernova... (The blast will be soo massive that poor little Proxima will also be totally erased).

Answer 2

If the two stars were the only thing in the whole universe, then the energy they use to generate gravitational waves (very, very little energy) would gradually make their orbital distance less and less.

However, I no not know enough about the effect of Proxima (the 3rd star in the system) and any surrounding matter in their neighbourhood. For example, if Proxima is eventually ejected from the system, then the energy required from the ejection will have come from the other two stars (they will approach each other faster). If Proxima is pulled inwards and spirals into one of the star, then the energy will be given back to the pair and they will move away from each other. (Unbalance trinary systems can be unstable over hundreds of billions of years).

The energy given off in gravitational waves by A and B is so small that maybe it is compensated by the fact that each star's "stellar wind" (and light) push against the other star. Or maybe not.

Maybe we also need to consider the influence of other stars in the general neighbourhood (including our Sun).

Answer 3

We find eccentric orbits in many things. They are just about as stable as circular ones. The only difference being if another body came by and perturbed the orbit, it could change it enough to cause a collision, or just become a different shape. Most highly elliptical orbits came about by this method anyway, or by being captured. You want to see eccentric? Look at Neptune's moon, Nereid.

Note, the far greater likelihood is that an orbiting smaller body would be ejected from the system. Collisions are relatively rare.