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White Dwarf Stars
There are several objects in astronomy which are classified as dwarfs. There are dwarf planets, dwarf stars and dwarf galaxies.
The classification of dwarf planet was created in 2006 by the International Astronomical Union after the discovery of Eris – a new object in the Kuiper Belt larger than Pluto. At their annual meeting, the IAU decided that there should be a new definition for planet. Planets must orbit the Sun, have enough gravity to pull themselves into a sphere, and have cleared out the other objects in their orbit. Objects which orbit the Sun, and are spheres, but haven’t cleared their orbit were classified as dwarf planets. Pluto, Ceres and Eris became the first dwarf planets under these new guidelines, with Haumea and Makemake added after.
A dwarf star is a relatively low-mass stellar object. There are many different kinds of dwarf stars, depending on their formation process. For example, a red dwarf star is a main sequence star with a much smaller mass than our Sun. They can last for billions of years, slowly and efficiently burning their fuel. A white dwarf star is a burned out remnant of a main sequence star, after it has used up all its fuel. A brown dwarf is a sub-stellar object which isn’t massive enough to ignite stellar fusion in its core. A black dwarf is the theorized final outcome of a white dwarf, after it has radiated away all of its heat.
And then there are dwarf galaxies. These are galaxies with a fraction of the number of stars as the larger grand spiral and elliptical galaxies. A dwarf galaxy merely contains several billion stars, far less than the 200-400 billion stars in the Milky Way. The Large Magellanic Cloud, for example, contains 20 billion stars. It’s believed that dwarf galaxies were once the building blocks of larger galaxies. They came together over billions of years, adding their stars and gas to create the largest galaxies in the Universe.
We have written many articles about dwarf celestial bodies for Universe Today. Here’s an article about Dwarf Galaxies, and here’s an article about Dwarf Planets.
If you’d like more information on Dwarf Planets, check out NASA’s Solar System Exploration Guide on Dwarf Planets, and here’s a link to NASA’s Discussion about White Dwarfs.
We’ve also recorded an entire episode of Astronomy Cast all about Dwarf Planets. Listen here, Episode 194: Dwarf Planets.
Sources:
NASA Dwarf Planets
NASA Stars
About Fraser Cain
Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.
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