Astronomers have discovered black holes ranging from a few times the Sun’s mass to tens of billions. Now a group of scientists has predicted that NASA’s Nancy Grace Roman Space Telescope could find a class of “featherweight” black holes that has so far eluded detection. Today, black holes form either when a massive star collapses or when heavy objects merge. However, scientists suspect that smaller “primordial” black holes, including some with masses similar to Earth’s, could have formed in the ...