There are a class of celestial objects much heavier than our systems Jupiter but about the same size. They are not really planets just balls of dense hot gas, but they are not really stars because they lack the mass to collapse and heat their core to ignite sustained fusion. These Brown Dwarves are probably one of the most common objects in our universe but little is known about them because until recently they were essentially impossible to find. With new tools and new techniques this fascinating class of in between are coming into focus.

Another fascinating article from Centauri Dreams.