Gaia’s second data release became available to everyone on April 25. The catalogue includes the brightness and location on the two-dimensional sky for 1.7 billion stars, measures the distance and motion of 1.3 billion of them, and measures the colour of about 1.4 billion. It also measures the surface temperature, radius, luminosity and radial velocity of around other 14,000 objects within the solar system.
By tracing the motions and positions of such a large number of stars, Gaia is not only revealing new details about our galaxy’s spiral arms and other structures, but it is also opening the window on previously hidden eras of the Milky Way’s history.
Together with the data first released in 2016 we can now, for instance, determine the colour and brightness of more than 4 million stars within 5,000 light-years of Earth. With this information, astronomers can observe the characteristics of stars at all stages of their lives, from the first ignition, through their middle ages, to the period when they become giants and their declining years as white dwarves. These data will allow astronomers to understand the life cycle of stars better.
The measurements could also help astronomers to predict exactly where dark matter – an unknown, invisible substance thought to make up most of the matter in the universe – resides in the galaxy. Gaia has found nearly 5,000 objects that can be followed by ground-based telescopes before they disappear. Most of these are supernovas, exploding stars, which may help to reveal the nature of dark energy that is causing the expansion of the universe to accelerate.
Gaia was launched in 2013 and has been scanning the sky with its two telescopes continuously ever since, with the aim of explaining how our Milky Way galaxy formed and evolved. The satellite contains two telescopes and other instrumentation, including cameras with nearly a billion pixels.
Gaia’s first data release in 2016 published the distances of around two million stars but did not include any radial velocities. Unlike Nasa’s Hubble telescope, which takes images of the sky, Gaia measures the distance, motion, brightness and colour of stars. These data are then processed by hundreds of scientists and software engineers to produce maps of the asteroids in our solar system and a three-dimensional chart of nearby stars.
The next data release by Gaia will be in 2020. This is expected to increase the numbers of stars with known radial velocities from the current seven million to around 30 million.