'Failed star' is the coldest radio wave source ever discovered

lines of energy radiate outward from a brownish star

Astronomers have spotted the coldest star-like body on record found to produce emissions at radio wavelengths. 

Cooler than a campfire here on Earth and smaller than Jupiter, the faint object called T8 Dwarf WISE J062309.94−045624.6 is an ultra-cool brown dwarf, often referred to as "failed stars" because, despite usually being larger than gas giants, they are still smaller than stars.