It's important to understand that a "binary system" is a system of two stars orbiting around a common center of mass. So, the question "Why the sun in a binary system?" is a bit misleading. The Sun is not part of a binary system.

Here's why:

* Our Solar System: Our Sun is the only star in our solar system. It's the dominant gravitational force, and all the planets, asteroids, and other objects orbit around it.

* Binary Systems: In a binary system, both stars are roughly equal in mass, causing them to orbit each other due to their mutual gravitational pull.

Possible Scenarios:

* A nearby binary system: There could be a binary star system relatively close to our Sun, but they wouldn't be gravitationally bound to it.

* The Sun was once part of a binary system: Some scientists theorize that the Sun might have formed in a binary system, but its companion star was ejected due to a gravitational interaction with other stars in the early universe.

So, while the Sun isn't currently part of a binary system, it might have been in the distant past. However, there is no evidence to suggest that it is currently part of a binary system.