This morning, the European Space Agency unveiled a new, highly detailed sky map of the Milky Way Galaxy that showcases the brightness and positions of nearly 1.7 billion stars. It’s the most comprehensive catalog of stars to date, and it includes precise details about many of the stars’ distances, movements, and colors as well. With the map’s release, astronomers are hoping to use this information to learn more about the structure of our galactic home and how it first formed billions of years ago.
The map came together with data from ESA’s Gaia spacecraft. Launched in 2013, the spacecraft sits nearly 1 million miles from Earth, and it’s continuously scanning the sky with two telescopes. To get a thorough view of the galaxy’s stars, the vehicle rotates once every six hours, mapping one big circle of the sky. The Gaia mission team also changes the position of the spacecraft’s axis, too, allowing the vehicle to cover the entire sky in two-month increments. By doing multiple scans of the full sky, ESA gets repeated measurements of the same stars again and again.
ESA released a preliminary map of Gaia’s data back in 2016 based on 14 months of scanning. That one showed the precise positions of more than 1.1 billion stars. But today’s map is overflowing with even more information, thanks to data gathered over the course of 22 months. The chart details the distances and motions of up to 1.3 billion stars, in addition to positions and brightness. Astronomers have been able to measure the colors of 1.3 billion stars, too, which is a characteristic that provides a lot of information about what the stars are made of and how old they are.
Plus, the Gaia data includes information about how fast some stars are moving toward us or away from us, in what is known as radial velocity. Astronomers were able to make this measurement for 7 million stars. “It’s a small number compared to the 1.7 billion, but it’s still the largest radial velocity survey ever conducted,” Anthony Brown, an astronomer at the Leiden Observatory who works on the Gaia mission, tells The Verge.
And it’s not just Milky Ways stars that Gaia mapped, either. The spacecraft found the positions of half a million distant galaxies, too, as well as objects much closer to home. Scientists pinpointed the positions of 14,000 asteroids in our Solar System thanks to Gaia data.
Gaia scientists hope this data will help astronomers further their understanding of the physics of stars. Knowing the distance of a star is crucial for figuring out how bright the object is, for instance. “[Distance] is the only way we can tell if a particular star looks bright in the sky because it’s intrinsically bright or that it happens to be nearby and is actually faint,” says Brown.
But above all, the new Gaia map will help astronomers piece together the history of the Milky Way’s formation. It’s thought that our galaxy grew into its current form after merging with much smaller galaxies billions of years ago, according to Brown. These small galaxies serve as the building blocks of our galactic home, and the catalog could show astronomers where the stars from these past systems are today. “These stars from the small galaxies of the past are spread out all over the sky, but you can still recognize they belong together by seeing that their orbits are all the same,” says Brown. “So the properties of the stars... allows us basically to do archeology of the Milky Way.”
As extensive as today’s map is, there’s even more information to come. The Gaia mission is planned to last for a full five years, and ESA scientists hope to extend the mission for an additional five years afterward. “That has the advantage, not so much that we will measure more stars, but all the measurements will become more accurate,” says Brown.