When two stars orbit a common centre of mass, they are called binary stars. These stars are gravitationally bound to each other. It is said that 85% of stars are in binary systems or in multiple systems.
Did you know that the light that we observe coming from a star in the sky may not be produced by a single star? That the light emanating from the single point may actually be light coming out from two or even more stars that are orbiting together? These are called multiple-star systems.
The most common star system that you come across will be a binary star system that comprises two stars. When two stars orbit a common centre of mass, they are called binary stars. These stars are gravitationally bound to each other.
Did you know that most stars are in binary systems? It is said that 85% of stars are in binary systems or in multiple systems.
While the brighter star is called the primary star, the dimmer one is called the secondary. If the stars are of equal brightness, then the discoverer gets to decide on the designation.
Binary stars are very important from an astronomic point of view as they help in understanding stellar evolution. They help determine the masses and luminosities of stars.
But how are these binary stars formed? The most common way of formation of a binary star system is by a process called fragmentation.
According to this, the gas and dust cloud which collapses to form a star splits into two or more stars due to their instability or cooling/heating effects.
These fragments or stars then evolve separately and form the binary star system. But there are rare incidents when a massive star captures a passing one, as the star travels through the galaxy and thereby creates a new binary pair.
Binary pairs can be classified based on a number of factors. One such classification is on how they are observed viz. visual binaries.
They are called visual binaries when the two stars have a wide separation when viewed through a telescope.
The first binary stars to be ever spotted were visual binaries. In 1617, at the behest of a scientist, Italian astronomer Galileo Galilei used his telescope to focus on a star at the end of the handle of the Big Dipper, a constellation.
It was discovered that this wasn't a single star, but two stars which later turned out to be six. Sir William Herschel, who is known for cataloguing 700 pairs of stars, used the term binary for the first time in 1802 to refer to the double stars.
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