Free Astronomy Magazine July-August 2020

32 SPACE CHRONICLES “We were totally surprised when we realised that this is the first stellar system with a black hole that can be seen with the unaided eye,” says Petr Hadrava, Emeritus Scientist at the Academy of Sciences of the Czech Republic in Prague and co-au- thor of the research. Located in the constellation of Telescopium, the system is so close to us that its stars can be viewed from the southern hemisphere on a dark, clear night without binoculars or a telescope. “This system contains the nearest black hole to Earth that we know of,” says ESO scientist Thomas Riv- inius, who led the study published today in Astronomy & Astrophysics . The team originally observed the system, called HR 6819, as part of a study of double-star systems. How- ever, as they analysed their observa- tions, they were stunned when they revealed a third, previously undiscov- ered body in HR 6819: a black hole. The observations with the FEROS spectrograph on the MPG/ESO 2.2- metre telescope at La Silla showed that one of the two visible stars or- bits an unseen object every 40 days, while the second star is at a large dis- tance from this inner pair. Dietrich Baade, Emeritus As- tronomer at ESO in Garching and co-author of the study, says: “The observations needed to determine ESO instrument finds closest black hole to Earth A team of astronomers from the European Southern Ob- servatory (ESO) and other in- stitutes has discovered a black hole lying just 1000 light-years from Earth. The black hole is closer to our Solar System than any other found to date and forms part of a triple system that can be seen with the naked eye. The team found evi- dence for the invisible object by tracking its two companion stars using the MPG/ESO 2.2-metre tele- scope at ESO’s La Silla Observatory in Chile. They say this system could just be the tip of the iceberg, as many more similar black holes could be found in the future. JULY-AUGUST 2020 by ESO