It's clear which is the biggest star in this binary system.

Based on recent results,
this artist's vision of the double star Phi Persei,
720 light years away, shows
a bright, massive star surrounded by a disk of gas and
with its small companion separated by about the distance from
the Earth to the Sun.

The bigger star is presently about 9 times more massive than
than the small one ... but it wasn't always this way.

Ten million years ago the small companion was actually the most massive
star in the system
and as a consequence evolved into a giant star more quickly.

After losing its swollen outer layers to its close companion,
all that now remains is a stripped down, 
intensely hot stellar core of about 1 solar mass -
leaving its companion the dominant mass in the system.

What does the future hold?
In another 10 million years, the roles may be reversed again as the
now massive star swells into its giant phase "returning" mass to
its companion.

Will these stars end as white dwarfs or supernovae?

astronomers consider the fate of such systems an open and interesting
question!

mass-exchanging interacting binary systems