H-R Diagram for Milky Way Stars

H-R Diagram for Milky Way Stars

In the Hertzprung-Russell diagram the temperatures of stars are plotted against their luminosities. The position of a star in the diagram provides information about its present stage and its mass. Stars that burn hydrogen into helium lie on the diagonal branch, the so-called main sequence. Red dwarfs like AB Doradus C lie in the cool and faint corner. AB Dor C has itself a temperature of about 3,000 degrees and a luminosity which is 0.2% that of the Sun. When a star exhausts all the hydrogen, it leaves the main sequence and becomes a red giant or a supergiant, depending on its mass (AB Doradus C will never leave the main sequence since it burns so little hydrogen). Stars with the mass of the Sun which have burnt all their fuel evolve finally into a white dwarf (left low corner).
Another H-R diagram showing a number of specific stars, as well as representative star sizes. The star sizes are somewhat to scale. Hertzsprung-Russel StarData ” by ESO is licensed under CC BY 4.0

The H-R diagram shown in illustration above provides stellar data in a different way. The four main groups of stars are clearly identified:

  1. Main Sequence: most stars, like our Sun; this is the area on the H-R diagram where most stars will spend their stellar lives.
  2. Supergiants: cool stars which are very large and very bright. These stars generally end with a supernova event and many collapse to become neutron stars and even further collapse to a black hole.
  3. Giants: cool stars which are a little smaller and dimmer than the Supergiants. The Giants have a different stellar ending than the Supergiants.
  4. White Dwarfs: very, very hot stars which are very small in size.

This particular H-R diagram is very informative in that it graphically shows relative sizes, (though not to scale), colors (thus temperatures), and in some cases masses when compared to the Sun (for example in the upper left-hand corner: 60 MSUN, which means a star 60 times the mass of the Sun). There are also a number of representative stars shown; for example:

  • Betelgeuse in the constellation Orion — X-axis: 3000K, Y-axis 10 SUN
  • Polaris, the north pole star — X-axis: 6000K, Y-axis between 10 and 10 SUN
  • Sirius, the brightest star visible from Earth after the Sun — X-axis: 9000K, Y-axis 10 and 10 SUN
  • Sirius B, the white dwarf companion of Sirius — o X-axis: ~25000K, Y-axis 0.1 and 10- SUN
  • The Sun — X-axis: 6000K, Y-axis 1 M SUN