Do Stars Orbits around Each Other, and Why Don’t They Collide?

Stars within our galaxy often orbit around one another, forming binary and multiple star systems. Despite their high speed and strong gravitational pull, the vastness of space and the physics governing these systems amazingly prevent them from colliding. Let's delve into the mysteries of star orbits and the factors responsible for their stability.

Binary and Multiple Star Systems in the Milky Way

According to astronomical research, there are millions of binary and multiple star systems in the Milky Way. These systems are not merely singularities but complex arrangements of celestial bodies that interact with each other. For instance, the bright star
Sirius
is a well-known binary system comprising Sirius A, a main-sequence star, and Sirius B, a faint white dwarf companion.

Orbit Dynamics and Energy Conservation

When two stars are in orbit, they are in a state of equilibrium that requires no energy to maintain. This equilibrium is based on the principle of energy conservation. It would take extra energy for a star to either escape or to collapse into another. This extra energy is often supplied by another star or a large celestial object, but such events are exceedingly rare.

In most cases, a star’s orbital path may change due to collisions or interactions with other objects. However, what often happens is that one or both of the stars may go supernova. This event is catastrophic but also stabilizing. After a supernova, the surviving stars continue to orbit each other, although the orbit might change due to the supernova’s mechanical and energetic impact.

Orbit Around the Barycenter

It is common to describe orbiting stars as orbiting each other. Technically, they orbit their common center of mass, known as the barycenter. Sirius A and Sirius B orbit this barycenter. The distance between them varies from 8.2 to 31.5 Astronomical Units (AU) with an orbital period of 50 years. This distance ensures that no collision occurs.

Famous Examples: Mizar and Alcor

Mizar and its dimmer companion, Alcor, form one of the most famous double star systems visible to the naked eye. These two stars are gravitationally bound and located within the circumpolar constellation Ursa Major, known as Saptharishi Mandala. Mizar itself is a double star, and it was the first double star known. It consists of two binaries, making it a quadruple system.

Alcor, the visible companion of Mizar, is a binary system composed of Alcor A and Alcor B. The Alcor binary system is gravitationally bound to the Mizar quadruple system, making it a sextuple system in total. Since Mizar is 1.2 light years away from Alcor, the risk of collision is negligible.

Contact Binary Systems

There are special types of binary systems called contact binary systems where the stars are so close that they touch each other and even share their gaseous envelopes. While most contact binary stars are stable, a few have become unstable and have merged in the past. Thus, the likelihood of stars colliding is greatest when they are close enough to share the same atmosphere.

Stability of Contact Binary Systems

Contact binary systems are fascinating. Seen from a distant planet, these systems exhibit unique characteristics. The diagram below illustrates a contact binary star system, emphasizing the proximity between the two stars and the shared atmosphere.

These diagrams and explanations provide a clearer picture of the intricate and delicate balance that keeps stars from colliding. Despite their speed and the strength of their gravitational pull, the vastness of space and the intricate nature of their orbits prevent them from coming into contact with each other.

Conclusion

The vastness of our galaxy and the complex orbital dynamics of stars ensure that while binary and multiple star systems are common, collisions are rare. Whether they orbit each other or their common barycenter, the sheer distances involved and the principles of orbital mechanics work to maintain these systems in lifelong harmony.