An excess of 'failed' stars is a bad sign for alien life

We know for a fact that life can exist on planets that orbit yellow dwarf stars like our sun and are optimistic about the chances for smaller red dwarf systems like Trappist-1. When it comes to their awkward brown dwarf cousins, however, astronomers don't think life is possible -- they're too small and cool to support it. So it's a bit of a bummer that astronomers have discovered as many as 100 billion brown dwarfs in our galaxy, out of a maximum 400 billion stars in total.