The Milky Way just got a little more crowded. The European Space Agency's Gaia spacecraft has mapped more than a billion stars in the galaxy with unprecedented accuracy and detail — and it has already discovered 400 million more previously unknown stars.
The stellar trove of 1.142 billion stars, released Wednesday, marks the first step toward building the most intricate three-dimensional map ever made of our galactic home.
Gaia could find roughly half a million quasars and shed light on the role of dark matter in our galaxy. Once complete, the mission's full five-year catalog could help scientists better understand how our spiral-armed home in the universe came to be.
"We will be able to understand how the galaxy itself works and [how] it's evolving," Alvaro Gimenez, ESA's director of science, said in a news briefing.
Although astronomers can stare so deep into the universe that they can see galaxies that are billions of light-years away, there's a lot we don't know about our own stellar neighborhood.
Stare at the Milky Way as it appears across the sky, and there's no sign of its disc-like spiral-armed structure, or that we happen to be sitting in one of its swirling limbs, said Timo Prusti, Gaia's project scientist at ESA.
"In a way, Milky Way is an easy target: Wherever you look, you look at Milky Way," he said. "At the same time, it's extremely difficult because in order to understand it completely, you have to look to all directions."
When you observe nearby stars, you have to take into account that they're all interacting with one another in complicated ways, he added — and Gaia needs to map them accurately enough to understand those movements. Those interactions will be key to understanding how the galaxy as a whole operates, and how it came to be.
Scientists believe that the clusters in which hundreds or thousands of young stars are born may have played a large role in the eventual structure of the Milky Way, because they were the first structures to take form. But they don't know much about them, including the details surrounding how and why some stars get expelled from the stellar cradle while others get to stick close to their place of birth. (Those expelled stars, scientists said, may have helped populate the galaxy.)
"If we want to understand how the Milky Way was formed, we need to understand how the stars were formed," said Antonella Vallenari, a scientist with the Istituto Nazionale di Astrofisica and the Astronomical Observatory of Padua, Italy.
Among the other questions Gaia will help answer: What kinds of stars can be found at various distances from the center? What are the chemical components of these different stars, and how do they move?
"Gaia has a very important role as one of the real cornerstone missions for the understanding of the universe," Gimenez said.
Launched in December 2013, Gaia set out to perform a full survey of our Galaxy by surveying about 1% of the sky, or about a billion stars. It would take astrometric measurements to carefully track the position and movements of stars, gather photometry readings to measure brightness and use a radial velocity spectrometer to measure how the star moves toward and away from us.
Over its first 14 months conducting science, the spacecraft has been sending back 40 gigabytes of data per day, and returned a total of about 490 billion astrometric measurements (along with 118 billion photometric and 10 billion spectroscopic measurements).
The data, which will provide a baseline for future missions that study stars in the Milky Way, are exceedingly precise: If Gaia were sitting on Earth, it would be able to pick out a coin on the face of the moon, according to ESA officials.
Gaia will even help to find more exoplanets — particularly Jupiter-like planets that, like the gas giants in our own solar system, sit far away from their home star.
While the researchers celebrated the new map of the Milky Way, they were already waiting for the five-year mission's next interstellar bounty in 2017.
"I am extremely happy with the data release today, but I am even more looking forward to what we will see in the future," said Fred Jansen, Gaia mission manager at ESA.