1 of 6

Binary Stars

2 of 6

What are binary systems?

  • A binary system occurs when two deep space objects come close enough so they start orbiting one another around a common barycenter.
  • A barycenter is the center of mass between 2 or more bodies
  • If the masses of the two bodies are equal, the barycenter is exactly in the middle of the two objects; if the masses differ, the barycenter will vary in distance from the two bodies. It will be closer to the greater mass, and further from the lesser mass. Why is this true?
  • The barycenter is always an imaginative point which the two deep space objects in a binary system orbit around.

3 of 6

Star binaries

  • Usually seen in the night sky as one star, which if the stars have long orbital periods, can be distinguished as a binary system through a powerful telescope.
  • If the stars orbit each other along our line of sight, we will see them “eclipsing” each other, so the luminosity of the binary system will appear to change. Astronomers can use spectroscopy to study these stars.
  • Spectroscopy is the study of electromagnetic waves and color as it is perceived in the visible spectrum. It allows to study the chemical composition of DSOs on an atomic level, along great distances.

4 of 6

A specific type of binary: main sequence star and a white dwarf

White dwarfs have strong gravitational pull, which means they sometimes “pull” a main sequence star into their orbit, form a barycenter, and because of gravitational force, start accreting matter from the companion star

White dwarfs are composed of carbon and oxygen which are the elements in the core of a red giant

5 of 6

What happens next?

  • As white dwarfs accrete enough material from the companion star, they reach a limit called Chandrasekhar limit of 1.44 solar masses.
  • Because the white dwarf cannot sustain any more mass, it collapses onto itself and produces something called a type 1A supernova.
  • Type 1A supernovae are used as standard candles to measure distances by astronomers. Standard candles are objects that always exhibit a known luminosity (because the conditions for the formation of type 1A supernova are the same, thus luminosity is the same)
  • The core of the white dwarf gets destroyed, leaving behind a trail of star dust
  • Here is an example of type 1A supernova, the Kepler remnant 20K ly away from Earth

6 of 6

Let’s watch an animation of how a type 1A supernova is formed from a binary star system:

​

​

https://youtu.be/-yEBVm5o97E

​

Fun fact: did you know that Jupiter and the Sun share a barycenter OUTISIDE of the Sun?

We all know that planets orbit around the Sun, but not all! Jupiter is so massive, that it shares a common orbital point with our star:

​

​

​