I have a few pet objects in astronomy that fascinate me endlessly. One of these is brown dwarfs, objects that are bigger than planets, but too small to be bona fide stars. They are much cooler and fainter even than dinky red dwarfs, making them very difficult to find… unless you are WISE:
[Click to embiggen.]
See that pale green dot in the middle? That’s a brown dwarf! I know, it’s not brown, it’s green, but that’s kosher since brown dwarfs are really magenta.
OK, hang on a sec. I’ll explain that in a minute.
The important thing is that this image shows a very nearby brown dwarf, maybe 18 – 30 light years away (the distance is hard to determine, but observations taken over the next year or so should pin it down). That’s really close! The nearest known star, Proxima Centauri (a faint red dwarf) is 4.2 light years away, and only a few hundred stars are within 30 light years. That makes this brown dwarf, named WISEPC J045853.90+643451.9 (after its location in the sky), one of the closest stars known.
You’d think think we’d have a pretty good idea of all the stars near us, since they’d be among the brightest in the sky. But in fact brown dwarfs are so faint that to optical telescopes they can escape detection even if they’re our cosmic neighbors. WISE, however, looks in the infrared, where brown dwarfs glow considerably brighter.
And that brings me to the weird colorful adjectives we use for these objects.