Binary star

Binary Stars

A binary star is a pair of stars that are connected and spin around each other. These stars are important for scientists who study space. They help us learn about how stars change over time and how much they weigh.

Sometimes, we can see two stars as one bright dot in the night sky. But with a telescope, we can see that they are really two stars close together. These are called visual binaries. Some of these pairs take hundreds or even thousands of years to go around each other.

The nearest binary star, Alpha Centauri, was photographed by the Hubble Space Telescope. It looks like one star to our eyes, but it is really two stars orbiting each other.

We can also find binary stars by watching how their light changes. When the stars line up just right, one star can pass in front of the other. This makes the pair look dimmer, like a flashlight being covered. These are called eclipsing binaries.

Famous examples of binary stars include Sirius, the brightest star in the sky, and Cygnus X-1, which has a black hole. Binary stars are also found in glowing clouds called planetary nebulae.

Binary stars have been noticed since telescopes were invented. Early examples include Mizar in the Big Dipper and Acrux in the Southern Cross.

The word "binary" was first used for pairs of stars by Sir William Herschel in 1802. He described stars that stay connected because of gravity.

Binary stars are grouped into four types based on how we study them: visually, by looking through telescopes; by watching changes in light patterns; by noticing brightness changes during eclipses; or by tracking small shifts in a star’s position.

Some binary stars fit into more than one group. Scientists study these stars to learn about how stars are born and how they change. About one-third of the stars in our Milky Way are part of binary or multiple star systems.