The movement of stars in the outskirts of our galaxy indicates important changes in history Milky Way. These and other equally impressive results come from a set of papers demonstrating the quality of Gaia’s early release of Data 3 (EDR3) from ESA, announced on December 3, 2020.

Astronomers from the Gaia Data Processing Consortium (DPAC) saw evidence of the Milky Way’s past by looking at the stars in the direction of the galaxy’s “anti-center”. This is in the exact opposite direction in the sky from the center of the galaxy.

The results come in the opposite place from one of the four “explanatory papers” released alongside Gaia data. Others are using Gaia data to provide a massive extension of the counts of nearby stars, derive the shape of the solar system’s orbit around the galactic center, and explore structures in two galaxies close to the Milky Way. The papers are designed to highlight the newly published improvements and data quality.

Version 3 of early Gaia data by numbers. Credit: ESA; CC BY-SA 3.0 IGO

What’s New in EDR3?

Gaia EDR3 contains detailed information on more than 1.8 billion sources, discovered by the Gaia spacecraft. This represents an increase of over 100 million sources compared to the previous data release (Gaia DR2), announced in April 2018. Gaia EDR3 also contains color information for nearly 1.5 billion sources, an increase of about 200 million sources on Gaia DR2. Plus more public resources are included Health The accuracy of the measurements has also improved.

“The new Gaia data promises to be a treasure trove for astronomers,” says Jos de Bruijne, Gaia’s vice scientist at ESA.

Data from more than 1.8 billion stars were used to create this map of the entire sky. It shows the total star density observed by the European Space Agency’s Gaia satellite and launched as part of Gaia’s early release of Data 3 (Gaia EDR3). Brighter regions indicate denser concentrations of stars, while dark areas correspond to patches of the sky where fewer stars are observed. Unlike a color brightness map which is optimized by brighter and more massive stars, this view shows the distribution of all stars, including faint and distant stars. The bright horizontal structure dominating the image is the plane of the galaxy. It is an oblate disk that hosts most of the stars of our galaxy. The bulge in the center of the image surrounds the center of the galaxy. Credit: ESA / Gaia / DPAC; CC BY-SA 3.0 IGO. Acknowledgments: A. Moitinho and M. Barros

To the center of the galaxy

The new Gaia data allowed astronomers to track various groups of older and younger stars toward the edge of our galaxy – the galactic anticenter. Computer models predicted that the Milky Way’s disk would grow larger over time as new stars were born. The new data allows us to see remnants of a 10 billion-year-old ancient disk, thus determining a smaller range compared to the current disk size of the Milky Way.

New data from these outer regions also reinforces evidence of another major event in the galaxy’s recent past.

The data shows that in the outer regions of the disk there is a component of slow-moving stars above the plane of our galaxy heading down towards the plane, and a component of fast-moving stars below the plane that is moving up. This unusual pattern was not expected before. It may be the result of a close collision between the Milky Way and the Sagittarius dwarf galaxy that occurred in the recent past of our galaxy.

The dwarf Galaxy Sagittarius contains a few tens of millions of stars and is currently in the process of being broken up by the Milky Way. The last corridor close to our galaxy wasn’t a direct hit, but that would have been enough to the point that its gravity disturbed some of the stars in our galaxy like a stone’s fall into the water.

The Large and Small Magellanic Cloud (LMC and SMC, respectively) are two dwarf galaxies that orbit the Milky Way. This image shows the stellar density of satellite galaxies as seen by Gaia in its early release of Data 3, released December 3, 2020. It is composed of layers of red, green, and blue, which mostly follow the oldest and middle ages. Age and younger stars, respectively. Credit: ESA / Gaia / DPAC; CC BY-SA 3.0 IGO. Acknowledgments: L. Chemin; X. Luri et al (2020)

Using Gaia DR2, the DPAC members have already found a subtle ripple in the motion of millions of stars indicating the effects of an encounter with Sagittarius sometime between 300 and 900 million years ago. Now, using Gaia EDR3, they have discovered more evidence pointing to its powerful effects on our galaxy’s disk of stars.

“The motion patterns of disc stars are different from what we used to believe,” says Teresa Antuga, University of Barcelona, ​​Spain, who worked on the analysis with colleagues at DPAC. Although the role of the dwarf galaxy is still debated in some quarters, Teresa says, “You could be a good candidate for all these disturbances, as some simulations from other authors show.”

Data from more than 1.8 billion stars were used to create this map of the entire sky. It shows the overall brightness and star color observed by the European Space Agency’s Gaia satellite and released as part of Gaia’s Early Data Release 3 (Gaia EDR3).
The brighter regions represent denser concentrations of bright stars, while the darker regions correspond to patches of the sky where fewer and fainter stars are observed. The image color is obtained by combining the total amount of light with the amount of blue and red light that Gaia recorded in each spot of the sky. The bright horizontal structure dominating the image is the plane of our Milky Way. It’s actually a flat disk seen from the edge that contains most of the galaxy’s stars. In the center of the image, the galactic center appears bright and crowded with stars. Credit: ESA / Gaia / DPAC; CC BY-SA 3.0 IGO. Acknowledgments: A. Moitinho.

Measuring the orbit of the solar system

Galactic history is not the only finding from Gaia EDR3 presentation papers. DPAC members across Europe have done further work to demonstrate the ultimate in data accuracy and the unique potential of unlimited scientific discovery.

In one paper, Gaia allowed scientists to measure the acceleration of the solar system with respect to the frame of the rest of the universe. Using the observed motions of very distant galaxies, the velocity of the solar system was measured to change at 0.23 nm / s every second. Due to this slight acceleration, the path of the solar system is deflected by a diameter corn Every second, and in the year this is about 115 km. The acceleration measured by Gaia shows good agreement with theoretical predictions and provides the first measurement of the curvature of the solar system’s orbit around the galaxy in the history of visual astronomy.

New Star Count

Gaia EDR3 also allowed new star count in the solar quarter. Gaia’s catalog of nearby stars contains 331,312 objects, which are estimated to be 92 percent of the stars within 100 parsecs (326 light-years) from the Sun. The previous solar neighborhood census, called the Gliese Catalog of Nearby Stars, was made in 1957. It contained only 915 objects at the start, but was updated in 1991 to 3803 celestial bodies. It’s also limited to a distance of 82 light-years: Gaia is four times more numerous and contains 100 times more stars. It also provides measurements of location, motion and brightness that are at volumes more accurate than historical data.

Data from version 3 of early Gaia data shows how stars are pulled from the Small Magellanic Cloud, and directed toward the adjacent Large Magellanic Cloud, forming a stellar bridge through space. Credit: ESA / Gaia / DPAC; CC BY-SA 3.0 IGO. Acknowledgments: S. Jordan, T. Sagristà, X. Luri et al (2020).

Beyond the Milky Way

A fourth illustration paper analyzed the Magellanic Cloud: two galaxies orbiting the Milky Way. After measuring the motion of the stars of the Large Magellanic Cloud more precisely than before, Gaia EDR3 clearly demonstrates that the galaxy has a spiral structure. The data also analyzes a stream of stars being pulled from the Small Magellanic Cloud, and hints at previously unseen structures on the outskirts of both galaxies.

At 12:00 CET on December 3, the data produced by the many scientists and engineers from the Gaia DPAC Consortium became available for everyone to see and learn from. This is the first in two parts; 3 full data release is planned for 2022.

“Gaia EDR3 is the result of a great effort from all involved in the Gaia mission. It’s a very rich dataset, and I look forward to the many discoveries that astronomers from around the world will make with this resource,” says Timo Proste, Gaia Project Scientist for the European Space Agency . “We’re not done yet; more fantastic data will follow as Gaia continues to make measurements from orbit.”