ESA's Gaia probe has been investigating the Milky Way for several years, and the first data release contained the exact location of more than 2 million stars. Now Gaia's second main dataset has determined the position and brightness of 1.7 billion stars in our galaxy. ESA has used this data to create the most detailed map of the Milky Way so far.
Gaia contains three instruments for observing stars, which enable him to determine the position, color and motion of stars over time. Gaia calculates the distance to stars, which astronomers consider the most critical data point, with parallax measurements. Gaia does this by examining the apparent motion of a star at two different points in its orbit, separating it from its true motion in the galaxy. The spacecraft will monitor each target star about 70 times over the course of five years, which corresponds to the planned mission duration. We are nearing the end of the mission, so Gaia has sent back a huge amount of data.
There are about 100 billion stars in the Milky Way, so it's still a drop in the bucket, if you know about a billion of them. However, previous measurements could only detect about 100,000 stars. With Gaia's data, scientists have determined the location and apparent brightness of 1.7 billion stars, but that's not all. The ESA has more details about an impressively large subset of these celestial bodies. We also know the color of 1.4 billion stars, the distance and the movement of 1.3 billion. For a smaller number of stars we have even more details. The ESA says 161 million stars now have accurate surface temperature measurements in the database, 77 million have known radii, and we know the radial velocity of 7 million.
In the image above, the ESA has created a map of the Milky Way from Gaia's perspective with location, color and brightness data. With Gaia data from 22 months of observations, scientists are closer to mapping the galaxy than ever before. Gaia's original mission mandate will expire at the end of this year, but it is likely that the ESA will grant an extension. Gaia has enough fuel to continue for another four years, provided there are no mechanical failures.
The Gaia mission itself is not meant to make the big discoveries. It's just a catalog of stars in the sky. Community scientists will use this data to explore the galaxy and learn more about their past, present and future.