It's clear who is the biggest star in this binary system. A small companion star orbits 100 million miles away. Ten million years ago the small companion was actually the most massive star in the system and because of its greater mass evolved into a giant star more quickly. After losing its swollen outer layers to the now massive star, all that remains is a stripped down, intensely hot core of about 1 solar mass. Astronomers consider the ultimate fate of such mass-exchanging, interacting binary systems an open question and a challenge for present theories of stellar evolution .
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