File:GEMs in the sky (and on the ground!) (potw2230a).jpg

English: Gazing up at the stars from the Chilean Atacama Desert is the newest addition to ESO’s La Silla Observatory: BlackGEM, an array of optical telescopes established to detect the sources of gravitational waves using visible light. While not present when this image was taken, a third dome has now been installed in the rightmost pillar.In partnership with observatories such as EGO-Virgo and LIGO, BlackGEM will search for some of the most dramatic events in the universe, including the collision of black holes and neutron stars. These events cause ripples in spacetime known as gravitational waves that detectors such as Virgo and LIGO can identify. BlackGEM is then able to pinpoint their location by searching the sky for short-lived astronomical events such as optical sources that appear or disappear within a single night. After BlackGEM has finished its measurements, other telescopes such as ESO’s Very Large Telescope (VLT) can make deeper follow-up observations in more detail, providing astronomers with insight into some of the universe’s most closely guarded secrets.Sparkling in the sky above BlackGEM is the Milky Way, bejewelled with stars and clouded with dark dust and bright gas. The haze of ruby red and emerald green which illuminates the scene is known as airglow and results mainly from chemical reactions between atoms high up in the atmosphere.