Astronomers know that stars are born in clouds of gas, but what sets off star formation, and how galaxies as a whole play into it, remains a mystery. To understand this process, astronomers have observed five nearby galaxies — NGC 1087, NGC 1300, NGC 3627, NGC 4254, and NGC 4303 — with the Multi-Unit Spectroscopic Explorer (MUSE) instrument on ESO’s Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA),...