OUTSIDE THE MILKY WAY

Total number of sources 1.8 billion (mostly stars) Binary star systems 813,000 Variable stars 10 million White dwarfs 500,000 Star clusters 2,500 Solar System objects 158,000 Quasar candidates 6.6 million Galaxy candidates 4.8 million When you're surveying between 1 and 2 billion stars, you can't help bagging numerous galaxies and quasars, too. Quasars are the luminous cores of remote galaxies, powered by supermassive black holes. They are found all over the sky, and since they don't exhibit parallax or proper motion, Gaia uses a selection of 1.6 million quasars as a reference frame — a coordinate system against which it measures stellar positions. But of course, quasars are interesting by themselves, just like the many galaxies studied by Gaia. DR3 includes two separate catalogues of extragalactic sources, containing 6.6 million quasar candidates and 4.8 million galaxy candidates, respectively. For…