The European Space Agency has released the most detailed star catalogue ever assembled, including high-precision measurements of nearly 1.7 billion stars along with the positions, distances and relative motions of more than one billion suns. Based on 22 months of data collected by ESA’s Gaia astrometry spacecraft, the survey includes some 14,000 asteroids, detailed observations of globular clusters orbiting the Milky Way’s halo and gravitationally bound dwarf galaxies.
The data even indicate the motions of stars within some globular clusters and the Small and Large Magellanic Clouds. The catalogue includes the orbits of 75 globular clusters and 12 dwarf galaxies orbiting the Milky Way, providing clues about the galaxy’s formation and evolution.
“With Gaia, we can actually deconstruct the whole history of the Milky Way,” Günther Hasinger, ESA director of Science, said at a briefing to unveil the new results. “It’s like archeoastronomy, to really build up the history of our universe.”
Launched in December 2013, Gaia’s first data release in 2016 revealed the distances and motions of about two million stars. The latest release, unveiled 25 April, pushes the total number of measured stars to nearly 1.7 billion with an accuracy in some cases equivalent to an Earth-bound observer resolving a Euro coin on the surface of the moon.
“It’s measuring solar system objects, it’s measuring stars, it’s not only measuring where they are on the sky but also how distant they are, how they’re moving through space, and this allows us to map things like our Milky Way disk, the Milky Way halo where we find the globular clusters,” said Anthony Brown of Leiden University, leader of the Gaia Data Processing and Analysis Consortium.
“And we can also look at our neighbour galaxies, the dwarf galaxies like the Magellanic clouds,” he said during the briefing to describe the new data release. “Finally, I should mention that Gaia also measures the very distant objects called quasars.”
Powered by supermassive black holes, quasars are “effectively infinitely distant,” Anthony said.
“One of the fundamental contributions of this data release is for the first time, we have an optical reference frame completely built from extra-galactic sources,” he said. “That’s somewhat technical, but really an amazing achievement.”
Gaia’s unprecedented precision allows researchers to separate the parallax of target stars — their apparent motion in the sky due to Earth’s movement around the Sun — and their true, or proper, motions in the galaxy. The new dataset includes parallax and proper motion data for more than 1.3 billion stars. The most accurate parallax measurements, about 10 percent of that total, provide the distances to those stars.
“The most eagerly awaited result from Gaia are so-called parallaxes, which is the measurement which gives the handle to the distance to the stars,” Tim Prusti, Gaia project scientist, said in an ESA video. “This is a very tough measurement to be done.
“We have known since Hipparcos, the previous ESA mission, distances to about 100,000 stars. Gaia is going to increase that number to about one billion, so that is a real revolution.”
“The sheer number of stars alone, with their positions and motions, would make Gaia’s new catalogue already quite astonishing,” Anthony said in an ESA statement. “But there is more. This unique scientific catalogue includes many other data types, with information about the properties of the stars and other celestial objects, making this release truly exceptional.”
Along with high-precision measurements of stellar positions, The Gaia data include brightness and colour measurements for nearly the entire surveyed population, along with similar measurements for a half million variable stars, key elements in refining models of stellar evolution.
The catalogue includes line-of-sight motion for some seven million stars, the surface temperatures of 100 million suns and the effects of interstellar dust on about 87 million suns. Analysis of the motions of stars within a few thousand light years indicates subtle patterns that may be the result of past mergers with smaller galaxies, the Milky Way’s spiral arm architecture or perturbations from a concentration of stars across the center of the galaxy.
Closer to home, the Gaia catalogue now includes the positions of more than 14,000 known asteroids, allowing precise determinations of their orbits. More asteroids will be added in subsequent data releases.
“Gaia will greatly advance our understanding of the Universe on all cosmic scales,” Prusti said in the agency’s statement. “Even in the neighbourhood of the Sun, which is the region we thought we understood best, Gaia is revealing new and exciting features.”
