What Is #15: A Blue Dwarf?

The 'What Is' Series

A couple of months ago I started a new series on this blog titled "What Is". Thus far the focus is on the field of astronomy where we hear all sorts of cool science taking place in space. The goal of this series is to explain the details of different objects we hear about relatively frequently.

Stars

I have recently covered Black Dwarfs, Brown Dwarfs, White Dwarfs, and Red Dwarfs. Brown Dwarfs are objects that were not quite large enough to fuse hydrogen, so they never reached full star status. White Dwarfs are the final stage of a low mass star such as the Sun. After these low mass stars shed away their outer layers, the stellar core leftover is called a White Dwarf. Black Dwarfs do not yet exist in the Universe, but eventually White Dwarfs will finally emit all of their energy, leaving behind a leftover core that no longer releases energy. This leftover core will be called a Black Dwarf. Red Dwarfs are the very low mass Main Sequence stars fusing hydrogen into helium in their cores. But there are also Blue Dwarfs. How do Blue Dwarfs differ from their cousins?

Blue Dwarfs

A Blue Dwarf is not a term that came up often in my astronomy studies and not something I spend much time on in the astronomy classes I now teach. But there is a class of stars called Blue Dwarfs, or rather, there WILL BE a class of stars called Blue Dwarfs. When Red Dwarfs exhaust their hydrogen supplies, these small stars will increase in luminosity and increase in surface temperature. The change in surface temperature will change the surface color from red to, eventually, blue. Thus these stars will become Blue Dwarfs. Red Dwarfs are very small stars and take tens of billions of years to evolve into Blue Dwarfs. As the Universe is only 13.8 billion years old, there are not yet any Blue Dwarfs in the Universe. This is similar to Black Dwarfs that will one day exist, but don't exist yet.