I was reading about the coolest stars, and was surprised to find about stars with a surface temperature lower than a candle, like 2MASS 0939-2448 A/B, of about 100 Celsius like CFBDSIR 1458+10B and even below 0 Celsius temperature where the water freezes like WISE J0855-0714. Then I thought, they might be stars where fusion only happens very deep in the core, and then I found out this:
In addition, many brown dwarfs undergo no fusion; those at the low end of the mass range (under 13 MJ) are never hot enough to fuse even deuterium, and even those at the high end of the mass range (over 60 MJ) cool quickly enough that after 10 million years they no longer undergo fusion.
Are these brown dwarfs which don't sustain any type of fusion considered stars? If so, what's the reason?