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The four sky maps made with the new ESA Gaia data released on 13 June 2022.

The Milky Way in four maps: data from the Gaia spacecraft show the speed at which stars move towards or away from us, known as radial velocity (top left); their radial velocity and proper motion, or how they move across the sky (bottom left); their chemical make-up (bottom right); and the interstellar dust (top right).Credit: ESA/Gaia/DPAC/CU6 (CC BY-SA 3.0 IGO)

Mega-map of Milky Way adds depth to stars’ motions

Astronomers’ main reference guide to the Milky Way has received a major update. The Gaia mission, in which a spacecraft is tracking nearly two billion stars, has released a vastly improved map. The map now includes the 3D motions of tens of millions of stars and thousands of asteroids — as well as the detections of stellar ‘quakes’ and of possible extrasolar planets.

The mission’s team unveiled the trove, which consists of 34 months’ worth of data, on 13 June.

Gaia was launched by the European Space Agency in 2013 and orbits the Sun at a fixed distance from Earth. It takes repeated measurements of the same stars from different perspectives. This makes each star’s apparent position change by a tiny angle — typically millionths of a degree — proportional to its distance. The mission team uses such changes and a technique called parallax to calculate the star’s distance from the Sun.

The biggest addition to the previous catalogue is the set of detailed spectra for about one million stars. By measuring a spectrum’s Doppler shift, the team has calculated 30 million ‘radial velocity’ measurements. Each indicates the speed at which a star is moving towards, or away from, the Sun. Together with Gaia’s measurements of the star’s motion across the sky and of its distance, the data provide a full reconstruction of the star’s trajectory as it circles the Galaxy.

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