> TRAPPIST-1 is an M8 dwarf, only 0.08 times the mass of the Sun; just barely massive enough to fuse hydrogen into helium in its core. If it were much lower mass we wouldn’t call it a star at all (we’d say it’s a brown dwarf).
And the Wikipedia article on brown dwarfs: https://en.wikipedia.org/wiki/Brown_dwarf
> Brown dwarfs are substellar objects not massive enough to sustain hydrogen-1 fusion reactions in their cores, unlike main-sequence stars.
Apparently TRAPPIST-1 is an actual star, which makes it a (small, cool) red dwarf, not a brown dwarf. But it is near the dividing line.
(A brown dwarf with planets would be interesting, but they probably wouldn't be potentially habitable.)
> TRAPPIST-1 is an M8 dwarf, only 0.08 times the mass of the Sun; just barely massive enough to fuse hydrogen into helium in its core. If it were much lower mass we wouldn’t call it a star at all (we’d say it’s a brown dwarf).
And the Wikipedia article on brown dwarfs: https://en.wikipedia.org/wiki/Brown_dwarf
> Brown dwarfs are substellar objects not massive enough to sustain hydrogen-1 fusion reactions in their cores, unlike main-sequence stars.
Apparently TRAPPIST-1 is an actual star, which makes it a (small, cool) red dwarf, not a brown dwarf. But it is near the dividing line.
(A brown dwarf with planets would be interesting, but they probably wouldn't be potentially habitable.)