Stellar Evolution

What Color is a Brown Dwarf?

Brown dwarfs are extremely low mass stars. They have masses only slightly larger than that of the planet Jupiter. Because a star's temperature depends on its mass (with smaller stars having cooler temperatures) brown dwarfs are extremely cool.

We know that as the temperature of a hot dense object decreases, it glows an ever duller red color. You can see this by watching an electric stove burner when you turn it off.

Are brown dwarfs such a dull red? Well, not quite. They are so cool that dust can condense in their atmospheres and mingled with the dust are sodium atoms. Sodium atoms absorb yellow light very strongly. If you take yellow light away from a dull red star, the star looks purple or magenta.

So brown dwarfs are actually purple!