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Are colored dwarves actualy colored or are they different kinds of stars?

Date: Thu Jan 23 08:51:03 1997
Posted by: Amanda Cooper
Grade level: 4-6
School/Organization: Harmony Middle
City: Overland Park State/Province: KS
Country: USA
Area of science: Astronomy
Message ID: 854031063.As


Are colored dwarfs actually colored or are they different kinds of stars?

Posted By: Malcolm Tobias, Graduate Student, Physics
Date: Fri Feb 21 12:15:35 1997

(This first paragraph was originally posted by Malcolm Tobias, and I added the rest later.)

When astronomers talk about colored dwarfs, they are usually referring to how bright the object is. Therefore a white dwarf is very bright, and a brown dwarf is very dark. Even though both of these objects are called dwarfs, the name is misleading since they are very different objects. White dwarfs are really small bright stars, with very high surface temperatures, but low luminosities. Even though they have about the same mass as our own sun, they are roughly 40 times smaller. Brown dwarfs are really large planets like Jupiter. Since they aren't stars they don't shine so astronomers refer to them as being brown, since they are very dark.

Here are some additional comments provided by Phil Plait.

I have a special page on my web site that talks all about star colors. Some of it is a bit technical so I'll tell you now that a star's color depends on the temperature of the star, and that there are lots of stars called "dwarfs" even though they are very different types of stars.

Hot stars are bluer, while cooler stars are red. There are lots of types of dwarf stars: the Sun is called a yellow dwarf, because it is relatively small and yellow (its temperature is about 6000 degrees Celsius). A red dwarf is a tiny red star, pretty much like the Sun but much cooler and smaller.

A white dwarf is a very different type of star: it is a star that used to be like the Sun but has used up its fuel. It contracts and gets very hot, sometimes as hot as 200,000 degrees! They are very small, about the size of the Earth.

Brown dwarfs are a newly discovered type of object, which are midway between stars and planets. They are too small to be real stars, but too big to be called planets. Several brown dwarfs have been recently discovered orbiting normal stars; you can find more about them at one of my favorite web sites, The Nine Planets, on the page called "Other Solar Systems?".

©2008 Phil Plait. All Rights Reserved.

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