That's no moon! Seriously -- it's a star, guys.
Y dwarfs are the dimmest stars of the brown dwarf family, like all brown dwarfs, they are not massive enough to fuse atoms at their cores. Without the atomic energy that allows stars like our sun to burn for billions of years, brown dwarfs gradually cool, until they only emit infrared light.
One of the Y dwarfs found, WISE 1828+2650, now holds the record for chilliest star at 80 degrees Farenheit.
Brown dwarfs help astronomers study star formation and the atmospheres of planets like Jupiter. Their atmospheres, similar in composition to the gas-giant planets, are often easier to observe because brown dwarfs are isolated in space, away from the light of more brilliant, parent stars.
Not gonna lie, being a brown dwarf sounds pretty depressing. "Isolated in space...away from the light of more brilliant, parent stars." Great, so not only are both your parents doctors, but you have to live alone in the woods. You know, this is how stars develop complexes.
Thanks to Braun, who's so bright his dad calls him son.