Not all stars travel alone in space. At least half of all stars in the night sky have a sister star and are part of a solar system where there are two or more suns, whose gravity keeps them in orbit around a common center of gravity.
Within 20 light years of here are 16 binary stars and two triple stars.
The Sun’s nearest neighbor is the triple star Alpha Centauri, where the two suns Alfa Cenauri A and B orbit each other in close proximity, while the third and faintest sun, Proxima Centauri, is somewhat further away.
Binaries form in the same cloud of gas and dust. These stars are therefore made of exactly the same elements and are also the same age. But sometimes their mass is uneven and they therefore develop unevenly and do not live very long. The more massive star dies earlier.
The twin of our sun
Some scientists even believe that all stars, including our Sun, formed as binaries.
This possible twin of the Sun is called Nemesis, and billions of years ago it hit an orbit, which has blown it out of the solar system.
According to this idea, Nemesis is most likely somewhere in the Milky Way and most likely a brown dwarf, which is a small, cool star that can never get hot enough to start nuclear fusion.
Three methods for finding binaries
Binaries revolve around a common center of gravity, but often only one star is visible. Astronomers therefore use special methods to find the twin.
1. Movement changes
Some binaries are discovered because the larger star’s motion pattern is irregular. Examples of this are Sirius and Sirius B in the Big Dog.
2. Blackout
In other cases, the orbits lie so that the stars shadow each other from here. An example of this is Algol in Perseus, whose brightness apparently wanes every third day.
3. Spectroscopic measurements
Two stars, very close to each other, are often only detected with a spectrometer that separates the light from the stars. With this method it was possible to reveal Kastor in Gemini, as a double star.
