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Will Capella Aa and Ab Merge When They Both Become Red Giants?

-- Russ | December 8, 2021

Question:

I understand that Capella Aa and Ab are yellow giant stars that have both exhausted their core hydrogen and are expanding. Since they’re only 0.74 AU apart, when they expand into red giants will their outer atmospheres merge? How will these two stars interact in their red giant stage?

-- Russ

Answer:

It is my understanding that both Capella Aa and Ab have exhausted their core hydrogen and evolved off the main sequence. One of them is already a Red Giant, while the other is evolving to that point, and is currently in the Hertzsprung gap on it path to becoming a Red Giant. I believe that these two stars are not projected to physically interact, even after the less-massive star in the binary reaches the Red Giant phase.

-- Jeff Mangum

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