Question

what would happen if you combined the two types of stars into a single H-R diagram?​

Answer 1

The H-R Diagram

A star's position on the H-R diagram tells you a great deal of information about it. The diagonal strip is called the main sequence. Main sequence stars are hydrogen-burning stars like our Sun. More massive main sequence stars are hotter, and are found at the top left of the strip. Less massive stars are cooler, and are found at the bottom right.

Massive stars burn through all their hydrogen quickly, in only a few million years. Smaller stars burn their hydrogen relatively slowly. Our Sun has been a main sequence star for about five billion years and will stay on the main sequence for another four to five billion years.

When stars have exhausted all their hydrogen fuel, they evolve to red giants. Their outer layers of gas expand and cool; therefore, the stars move to the right on the H-R diagram. Although a star cools when it becomes a red giant, it grows so large its luminosity (or total power emitted) increases. Therefore, the star also moves up the H-R diagram. The region above and to the right of the main sequence is occupied by the red giants.

When a red giant exhausts its fuel, its fate depends on its mass. Large red giants become neutron stars or black holes. Neutron stars are too faint to see in SDSS data and black holes, well, they are black!

Smaller stars, like our Sun, become white dwarf stars. White dwarfs are the cores of stars that have exhausted all their nuclear fuel. They are very hot when formed, but they are not very luminous because they are so small. White dwarfs are less luminous and hotter than main sequence stars, so they lie below and to the left of the main sequence on the H-R diagram. They will not be commonly seen in the data for this project, but there may be a few.