This image shows the paths of 40,000 stars located within 326 light-years of the solar system over the next 400,000 years, based on measurements and projections from the European Space Agency's Gaia spacecraft. (Image credit: ESA/Gaia/DPAC)
A treasure trove of data is set to answer some big questions about our galaxy.
The data, compiled by the European Space Agency's Gaia mission, contains an unprecedented amount of information about more than 1 billion of the brightest objects in the sky. Astronomers hope the new data, which will be released June 13, will help solve some major mysteries about the birth and life of the Milky Way and the stars in it.
The Gaia mission launched in 2013 and is known for creating the most detailed map of the Milky Way by charting the precise positions, distances and velocities of nearly 2 billion stars. The upcoming data set will add a new dimension: It will reveal the chemical compositions of tens of millions of stars, allowing astronomers to answer important questions.
Hovering around Lagrange Point 2 (not too far from another groundbreaking mission, the James Webb Space Telescope), Gaia scans the entire sky about every two months. The 2 billion celestial objects the telescope sees make up only about 1% of the total stars in the Milky Way. But with the help of sophisticated computer algorithms and a lot of scientific knowledge, astronomers can extrapolate those measurements to learn about the galaxy as a whole.
Here are some of the most fascinating mysteries the Milky Way explorers are eager to crack with the new data.
By measuring the precise positions, distances and velocities of vast quantities of stars, Gaia does much more than map the Milky Way as it is today. Because objects in the universe follow the rules of physics, astronomers can model the past trajectories of those stars and essentially play the movie of the Milky Way backward and forward millions, or even billions, of years. But that was already possible with the previously released data. With the new data set, astronomers will be able to look for more.
For the first time, the Gaia mission team will release what they call "astrophysical parameters" for half a billion stars. These parameters, derived from the light spectra of the stars measured by Gaia (which are essentially the fingerprints of how these stars absorb light), reveal information about the chemical composition, mass, age, temperature and brightness of each of the measured stars. And that is a big deal, Gaia project scientist Jos de Bruijne told Space.com.
The Milky Way has four spiral arms, but astronomers still debate about their sizes and positions.(Image credit: NASA/JPL-Caltech)
"You will really get to know the stars," De Bruijne said. "They basically tell you who they are. It's like having an anonymous group of 500 million people and now you get to know every single one of them — their names, how old they are, where they came from."
For 30 million of these stars, Gaia measured the chemical composition of stellar atmospheres, which is identical to the chemical composition of the molecular clouds that these stars were born in billions of years ago, De Bruijne said. By combining the information about chemical composition with the modeling of the stellar trajectories, astronomers will be able to track groups of stars to their birthplaces inside (but also outside) the Milky Way.
"It's really unique that we now can do this with such a high number of stars," De Bruijne said. "That's something that is otherwise really difficult and expensive to do with ground-based telescopes, as it takes a lot of time."
Although Gaia has been scanning the Milky Way since 2014, there is still a lot astronomers don't understand about the galaxy. Studying our galactic home is not an easy task. Because we are inside the galaxy, we cannot "see the forest for the trees." It is impossible even for Gaia to peer through the thick dust and gas clouds obscuring the Milky Way's center (where the recently photographed supermassive black hole Sagittarius A* lurks) to the other side of the galactic disk.
But through the gradual improvements in Gaia data — and with the help of other observation techniques, such as radio astronomy — the big picture is coming together, piece by piece. That means we're getting closer to solving some of the great puzzles, including the distribution of dark matter in the galaxy.
"All the stuff in the galaxy is exerting gravity at every star, and this gravity determines how fast the star moves," De Bruijne said. "So by measuring motions of stars, you also probe the matter distribution in the Milky Way. And that is really important for figuring out how the galaxy hangs together."
One of the lingering uncertainties related to the distribution of stars in the Milky Way is the galaxy's trademark spiral structure. Astronomers mostly agree that the Milky Way has four spiral arms, the dense twisting streams of stars and gas that appear to emanate from the galaxy's center. But there are quite a few points of contention around these spiral arms: Astronomers still debate the size and prominence of the individual arms, as well as their exact position in the Milky Way's disk. The new data might help reveal the spiral structure with better clarity.
"With the astrophysical parameters that we now have, we can directly create samples of stars for specific science cases," De Bruijne said. "We know that the spiral arms are mostly made of young stars. It's where stars form. So, with the new data, we can look, for instance, at stars that are no older than 100 million years." (In stellar terms, 100 million years is infancy. For comparison, our sun is 4.6 billion-year-old and will die in 5 billion years.)