Gaia’s Map of 1.3 Billion Stars Makes for a Milky Way in a Bottle

Call it a galaxy in a bottle.

Dennis Overbye

Last Wednesday, astronomers in Europe released a three-dimensional map of the Milky Way. It is the most detailed survey ever produced of our home galaxy. It contains the vital statistics of some 1.3 billion stars — about one percent of the whole galaxy. Not to mention measurements of almost half a million quasars, asteroids and other flecks in the night.

Analyzing all these motions and distances, astronomers say, could provide clues to the nature of dark matter. The gravity of that mysterious substance is said to pervade space and sculpt the arrangements of visible matter. Gaia’s data could also reveal information about the history of other forces and influences on our neighborhood in the void. And it could lead to a more precise measurement of a historically troublesome parameter called the Hubble constant, which describes how fast the universe is expanding.

The map is the latest result from the European Space Agency’s Gaia mission, which was launched into an orbit around the sun in December 2013. It was built by an international collaboration of European astronomers and universities as the successor to the Hipparcos satellite, which charted the positions of about 2 million stars. Gaia’s cameras find the distances to stars by triangulation, measuring how their images shift against background stars and quasars as the spacecraft swings from one side of its orbit to the other — a baseline of about 186 million miles. A preliminary data release, containing information on 2 million stars, was published in 2016.

The new data set is based on 22 months, from July 2014 to May 2016, of staring at the sky. The first sifting of these stars has led to new insights into the types and colors and ages of the stars, and has allowed astronomers to distinguish subsets of stars with different histories and origins in the galaxy, which could lead to a better account of how and when the Milky Way formed. The mission continues. The final Gaia catalog, expected in the early 2020s, will include positions, motions, brightnesses and other parameters of over a billion more stars. There is Big Data and then there is Cosmic Data.

“Gaia is astronomy at its finest,” said Fred Jansen, of ESA, the mission’s manager.

Parallax and proper motion on the sky - 360° viewCreditCreditVideo by ESA Science & Technology

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