The Incredible Stellar Density of the Galactic Center

A view of the Sagittarius-I Window, a star field near the center of the Milky Way containing about 2.8 million stars packed into 0.6 square degrees of sky

Credit: ESA/Gaia/DPAC — A part of the Sagittarius-I (Sgr-I) Window, observed by the astrometric satellite Gaia on February 7, 2017. The field of view covers about 0.6 square degrees of sky. In it, some 2.8 million stars are crowded, most of them belonging to the galactic bulge

Gaia is a space telescope launched by ESA in 2013, whose mission is to gather astrometric data (position, distance, proper motion, radial velocity) of over 1.8 billion stars in the Milky Way with the highest possible precision.

A complicated series of mirrors inside the satellite sends starlight to a giant camera, which records brightness values ​​through a series of CDDs that collectively provide nearly 1 billion pixels — it’s the largest and most powerful camera ever sent into space.

In just one hour, Gaia can record information on about two million stars. It produces about 50 gigabytes of data in a single day, the equivalent of over 10 DVDs. It is an enormous mass of information that the satellite sends via radio to several data processing centers on Earth.

Despite such an ability to record and process data, some sky regions are so crowded with stars that not even Gaia can handle them adequately. So, to maintain high precision standards in the data gathered, the procedure used while observing those regions is different…