Brown dwarfs are poorly named: they're not really brown. They're objects that are too small to really be called stars; they lack the oomph needed to fuse hydrogen into helium in their cores, which is the the mark of a true star. Because of this, they are far cooler than actual stars. Since cool stars are red, you'd think brown dwarfs would actually be really red. And they are. Unless they're blue. Yeah, let me explain this one. First, here are two images of a newly discovered brown dwarf, perhaps the coolest ever seen, and certainly one of the closest to the Earth:
[Click to redgiantize.] The star SDSS1416+13A is the brighter one in the image, and is a regular ol' brown dwarf. The other star is its lower mass and cooler companion, called SDSS1416+13B. How cool is it? Scientists estimate that it's at about 200 Celsius (400° F). I ...
