Images obtained of two stars in the process of a merger

Some of the structures present in the area around the recently described star system.

Enlarge / Some of the
structures present in the area around the recently described star
system.

We know two facts about our galaxy that are, in isolation,
mundane. One is that many stars are part of a two-star system and
may orbit each other at distances similar to those of the planets
in our own Solar System. The second is that stars that are similar
in mass to the Sun will end their fusion-driven existences by
expanding into bloated red giants. Put those two facts together and
you have an inescapable and intriguing consequence: a lot of stars
are going to end up expanding enough to swallow their neighbor.

What happens then can be hard to understand, in part because
there are so many potential options. If the companion star is
massive enough, the transfer of mass could trigger its explosion.
It’s also possible that friction could bleed energy from the orbit
of the companion star, reducing its orbit until it is merged. Or,
because the outer layers of the red giant are so diffuse, it’s
possible that the cores of the two stars could end up sharing a
single envelope, continuing to orbit each other.

While it’s easy to know when we’ve observed an explosion, it’s
much harder to figure out when we’re looking at either of the
latter two options. Normally, we’d rely on physical models to tell
us what would happen in these cases, but generating a model of
these conditions has turned out to be pretty complex. Now, however,
some researchers are suggesting that a common-envelope binary star
is the best way of explaining an object they’ve imaged.

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Source: FS – All – Science – News
Images obtained of two stars in the process of a merger