A tale of two black holes

What can the surprisingly huge mass of the black holes detected by LIGO tell us about dark matter and the early universe? The historic detection of gravitational waves announced earlier this year breathed new life into a theory that's been around for decades: that black holes created in the first second of the universe might make up dark matter. It also inspired a new idea: that those so-called primordial black holes could be contributing to a diffuse background light. The connection between the...