This morning, the European Space Agency unveiled a highly detailed new celestial map of the Milky Way that shows the brightness and positions of almost 1.7 billion stars. It is the most complete catalog of stars to date and includes precise details about the distances, movements and colors of the stars. With the launch of the map, astronomers hope to use this information to learn more about the structure of our galactic home and how it was formed billions of years ago.
The map was linked to the data from the ESA Gaia spacecraft. Launched in 2013, the spacecraft is almost a million miles from Earth, and continuously explores the sky with two telescopes. To get a complete view of the stars of the galaxy, the vehicle rotates once every six hours, mapping a large circle of the sky. The Gaia mission team also changes the position of the spacecraft's axis, allowing the vehicle to cover the entire sky in two-month increments. By performing multiple full-sky scans, ESA obtains repeated measurements of the same stars over and over again.
ESA published a preliminary map of the Gaia data in 2016 based on 14 months of scanning that showed the precise positions of more than 1.1 billion stars But today's map is replete with even more information, thanks to the data collected over the course of 22 months. The chart details distances and movements of up to 1.3 billion stars, in addition to positions and brightness. Astronomers have also been able to measure the colors of 1.3 billion stars, which is a feature that provides a lot of information about what stars are made of and how old they are.
In addition, the Gaia data includes information about how fast some stars move toward us or away from us, in what is known as radial velocity. Astronomers could make this measurement for 7 million stars. "It's a small number compared to 1,700 million, but it's still the largest radial velocity survey ever," says Anthony Brown, astronomer at the Leiden Observatory working on the Gaia mission, The Verge .
And it's not just the stars of Milky Ways that Gaia assigned. The spacecraft also found the positions of half a million distant galaxies, as well as objects much closer to home. The scientists identified the positions of 14,000 asteroids in our Solar System thanks to the Gaia data.
Gaia scientists hope that this data will help astronomers deepen their understanding of the physics of stars. Knowing the distance of a star is crucial to find out how bright the object is, for example. "[Distance] is the only way we can see if a particular star looks bright in the sky because it's intrinsically bright or it's close and it's really weak," says Brown.
But above all, the new map of Gaia will help astronomers to reconstruct the history of the formation of the Milky Way. It is believed that our galaxy grew to 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 of these past systems are today. "These stars from the small galaxies of the past spread throughout the sky, but you can still recognize that they belong together when you see that their orbits are all the same," says Brown. "So the properties of the stars … basically allow us to do archeology of the Milky Way."
As extensive as today's map is, there is still more information to come. Gaia's mission will last five full years, and ESA scientists hope to extend the mission for another five years. "That has the advantage, not so much that we measure more stars, but that all the measurements will be more accurate," says Brown.