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The stellar movement of Gaia for the next 400 thousand years. The stars are in constant motion. To the human eye, this movement, known as self-movement, is imperceptible, but Gaia measures it with increasing precision. The traces in this image show how 40,000 stars, all located within 100 parsecs (326 light years) of the Solar System, will move across the sky in the next 400,000 years. These suitable moves are released as part of Gaia Early Data Release 3 (Gaia EDR3). They are twice as accurate as the proper moves launched on the previous Gaia DR2. The increase in precision is because Gaia has now measured stars more times and over a longer time interval. This represents a major improvement on Gaia EDR3 over Gaia DR2. Credit: ESA / Gaia / DPAC; CC BY-SA 3.0 IGO. Acknowledgments: A. Brown, S. Jordan, T. Roegiers, X. Luri, E. Masana, T. Prusti and A. Moitinho.
The movement of the stars on the outskirts of our galaxy points to significant changes in the history of the Milky Way. This and other equally fascinating results come from a set of articles demonstrating the quality of ESA’s Gaia Early Data Release (EDR3), which is released on December 3, 2020.
Astronomers from the Gaia Data Processing and Analysis Consortium (DPAC) saw evidence of the Milky Way’s past by looking at the stars in the direction of the galaxy’s ‘anticenter’. This is exactly in the opposite direction in the sky from the center of the galaxy.
The results on the anticenter come from one of four ‘demonstration papers’ published alongside the Gaia data. The others use data from Gaia to provide a large survey of nearby stars, derive the shape of the Solar System’s orbit around the center of the galaxy, and probe structures in two galaxies near the Milky Way. The articles are designed to highlight the improvements and quality of the newly published data.
Gaia’s Early Data Release 3 in figures. Credit: ESA; CC BY-SA 3.0 OIG
What’s new in EDR3?
Gaia EDR3 contains detailed information on more than 1.8 billion sources, detected by the Gaia spacecraft. This represents an increase of over 100 million sources over the previous data release (Gaia DR2), which was made public in April 2018. Gaia EDR3 also contains color information for around 1.5 billion sources, an increase of approximately 200 million sources on Gaia DR2. In addition to including more sources, the accuracy and the accuracy of measurements has also improved.
“The new Gaia data promise to be a treasure trove for astronomers,” says Jos de Bruijne, deputy scientist for ESA’s Gaia project.
Data from more than 1.8 billion stars have been used to create this map of the entire sky. It shows the total density of stars observed by ESA’s Gaia satellite and published as part of Gaia’s Early Data Release 3 (Gaia EDR3). The brighter regions indicate denser concentrations of stars, while the darker regions correspond to patches of the sky where fewer stars are observed. In contrast to the color brightness map that is enhanced by the brightest and most massive stars, this view shows the distribution of all stars, including faint and distant ones. The bright horizontal structure dominating the image is the plane of the galaxy. It is a flattened disk that houses most of the stars in 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. Acknowledgment: A. Moitinho and M. Barros
To the galactic anticenter
The new data from Gaia has allowed astronomers to trace the various populations of older and younger stars to the very edge of our galaxy: the galactic antcentric. Computer models predicted that the disk of the Milky Way will grow over time as new stars are born. The new data allows us to see the relics of the 10 billion-year-old disk and thus determine its smaller extent compared to the current size of the Milky Way disk.
The new data from these outer regions also reinforces evidence for another major event in the galaxy’s more recent past.
The data show that in the outer regions of the disk there is a component of slow-moving stars above the plane of our galaxy moving downward toward the plane, and a component of fast-moving stars below the plane moving toward up. This extraordinary pattern had not been anticipated before. It could be the result of the near collision between the Milky Way and the Sagittarius dwarf galaxy that took place in our galaxy’s most recent past.
The Sagittarius dwarf galaxy contains a few tens of millions of stars and is currently in the process of being cannibalized by the Milky Way. Its last step close to our galaxy was not a direct impact, but this would have been enough for its gravity to disturb some stars in our galaxy like a stone falling into water.
The Large and Small Magellanic Clouds (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 Data Release 3, which was released on December 3, 2020. It is made up of red, green, and blue layers, primarily tracing ages and stars. younger respectively. Credit: ESA / Gaia / DPAC; CC BY-SA 3.0 IGO. Credit: L. Chemin; X. Luri and others (2020)
Using Gaia DR2, DPAC members had already found a subtle ripple in the motion of millions of stars that suggested the effects of the Sagittarius encounter sometime between 300 and 900 million years ago. Now, using Gaia EDR3, they have discovered more evidence pointing to its strong effects on the disk of stars in our galaxy.
“The movement patterns in the stars on the disk are different than what we used to believe,” says Teresa Antoja, University of Barcelona, Spain, who worked on this analysis with colleagues from DPAC. Although the role of the Sagittarius dwarf galaxy is still debated in some quarters, Teresa says that “it could be a good candidate for all these disturbances, as some simulations by other authors show.”
Data from more than 1.8 billion stars have been used to create this map of the entire sky. It shows the full brightness and color of the stars as observed by ESA’s Gaia satellite and published as part of Gaia’s Early Data Release 3 (Gaia EDR3).
The brighter regions represent denser concentrations of bright stars, while the darkest regions correspond to patches of the sky where fewer and fainter stars are observed. The color of the image is obtained by combining the total amount of light with the amount of blue and red light recorded by Gaia in each part of the sky. The bright horizontal structure dominating the image is the plane of our galaxy, the Milky Way. It is actually a flattened disk seen on edge that contains most of the stars in the galaxy. In the middle of the image, the galactic center appears bright and full of stars. Credit: ESA / Gaia / DPAC; CC BY-SA 3.0 IGO. Thanks: A. Moitinho.
Measuring the orbit of the Solar System
The history of the galaxy is not the only result of the Gaia EDR3 demonstration documents. DPAC members across Europe have done other work to demonstrate the extreme fidelity of the data and the unique potential for limitless scientific discovery.
In a paper, Gaia has allowed scientists to measure the acceleration of the Solar System relative to the rest frame of the Universe. Using the observed motions of extremely distant galaxies, the velocity of the Solar System has been measured to change by 0.23 nm / s per second. Due to this small acceleration, the path of the Solar System is deflected by the diameter of a atom every second, and in a year this adds up to about 115 km. The acceleration measured by Gaia shows good agreement with theoretical expectations and provides the first measurement of the curvature of the Solar System’s orbit around the galaxy in the history of optical astronomy.
A new stellar census
Gaia EDR3 has also made it possible to obtain a new census of stars in the solar neighborhood. Gaia’s Catalog of Nearby Stars contains 331,312 objects, estimated to be 92 percent of the stars within 100 parsecs (326 light years) of the Sun. The previous census of the solar neighborhood, called the Gliese Catalog of Nearby Stars , was carried out in 1957. Initially it had only 915 objects, but it was updated in 1991 to 3803 celestial objects. It was also limited to a distance of 82 light-years: Gaia’s census goes four times as far and contains 100 times as many stars. It also provides location, motion, and brightness measurements that are orders of magnitude more accurate than old data.
Data from Gaia’s Early Data Release 3 show how stars are pulled out of the Small Magellanic Cloud and into 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 demo article looked at the Magellanic Clouds: two galaxies orbiting the Milky Way. Having measured the motion of the stars in the Large Magellanic Cloud more precisely than before, Gaia EDR3 clearly shows that the galaxy has a spiral structure. The data also resolves a stream of stars being pulled out of the Small Magellanic Cloud, hinting at never-before-seen structures on the outskirts of both galaxies.
At 12:00 CET on December 3, the data produced by the many scientists and engineers of the Gaia DPAC Consortium is made public for anyone to view and learn from. This is the first of a two-part release; The full data release 3 is planned for 2022.
“Gaia EDR3 is the result of a great effort by everyone involved in the Gaia mission. It is an extraordinarily rich data set and I look forward to the many discoveries that astronomers around the world will make with this resource, ”says Timo Prusti, ESA’s Gaia project scientist. “And we are not done yet; More great data will follow as Gaia continues to make measurements from orbit. “
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