Free Astronomy Magazine July-August 2023

JULY-AUGUST 2023 observations, which will help to shed light on some of the most extreme events in the cosmos. T his drone shot, taken at ESO’s La Silla Observatory, shows a close- up of the open domes of the Black- GEM array. The three 65-cm telescopes that make up the array are visible inside. [ESO] To date, however, only one visible counterpart to a gravitational-wave source has ever been detected. Fur- thermore, even the most advanced gravitational-wave detectors such as LIGO or Virgo cannot precisely iden- tify their sources; at best, they can narrow the location of a source down to an area of approximately 400 full moons in the sky. BlackGEM will efficiently scan such large re- gions at high enough resolution to consistently locate gravitational- wave sources using visible light. BlackGEM’s three constituent tele- scopes were built by a consortium of universities: Radboud University, the Netherlands Research School for As- tronomy, and KU Leuven in Belgium. The telescopes are each 65 centime- tres in diameter and can investigate different areas of the sky simultane- ously; the collaboration eventually aims to expand the array to 15 tele- scopes, improving its scanning cover- age even more. BlackGEM is hosted at ESO’s La Silla Observatory in Chile, T his photo- graph shows a BlackGEM tele- scope sitting in- side its dome. The BlackGEM array, comprising three 65-cm tele- scopes, is located at La Silla Obser- vatory. [ESO] making it the first array of its kind in the southern hemisphere. “Despite the modest 65-centimetre primary mirror, we go as deep as some proj- ects with much bigger mirrors, be- cause we take full advantage of the excellent observing conditions at La Silla,” says Groot. Once BlackGEM precisely identifies a source of grav- itational waves, larger telescopes such as ESO’s Very Large Telescope or the future ESO Ex- tremely Large Tele- scope can carry out detailed follow-up