Ryan Urquhart

Terzan 5 is a globular star cluster, a tight swarm of hundreds of thousands of stars squeezed into a sphere a few dozen light-years across. In such a crowd, stars exchange matter and spin each other up, and some turn into pulsars — rapidly rotating neutron stars that emit radio pulses like lighthouses. New images taken with the Karl G.

A dim lightbulb suddenly starts illuminating patterns on the wall that were invisible to the eye. That's roughly how astronomers look at distant dwarf galaxies — tiny stellar islands poor in heavy elements. In some of them, a faint violet glow of ionized helium has been spotted (a specific spectral line He II 4686 Å).