The movement of stars on the periphery of our galaxy suggests significant changes in the history of Milky Way. This and other equally fascinating findings come from a series of documents demonstrating the quality of ESA’s Gaia Early Third Data Release (EDR3), which is released on December 3, 2020.
Astronomers from the Gaia Data Processing and Analysis Consortium (DPAC) have seen 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 anti-center results come from one of four “demonstration documents” released along with the Gaia data. The others use Gaia’s data to provide a huge extension to the census of nearby stars, derive the shape of the orbit of the Solar System around the center of the galaxy, and probe structures in two galaxies close to the Milky Way. The documents are designed to highlight the improvements and quality of the newly published data.
What’s new in EDR3?
Gaia EDR3 contains detailed information on over 1.8 billion sources, detected by the Gaia probe. This represents an increase of over 100 million sources from the previous data release (Gaia DR2), which was made public in April 2018. Gaia EDR3 also contains color information for approximately 1.5 billion sources, an increase of about 200 million sources compared to Gaia DR2. In addition to including multiple sources, the general precision and the accuracy of the measurements has also improved.
“The new Gaia data promises to be a treasure trove for astronomers,” says Jos de Bruijne, ESA’s Deputy Project Scientist.
At the galactic anticenter
The new data from Gaia allowed astronomers to trace the various populations of older and younger stars towards the edge of our galaxy – the galactic anticenter. Computer models predicted that the Milky Way disk will grow larger over time as new stars are born. The new data allows us to see the relics of the ancient 10-billion-year-old disk and thus determine its extent smaller than 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 shows that in the outer regions of the disk there is a component of slowly moving stars above the plane of our galaxy that are heading downward towards the plane and a component of fast-moving stars below the plane that are moving. upward. This extraordinary model was not anticipated before. It could be the result of the near collision between the Milky Way and the dwarf galaxy of Sagittarius that took place in our galaxy’s more recent past.
The dwarf galaxy of Sagittarius contains a few tens of millions of stars and is currently in the process of being cannibalized by the Milky Way. Its last close pass to our galaxy was not a direct hit, but it would have been enough for its gravity to perturb some stars in our galaxy like a stone falling into water.
Using Gaia DR2, DPAC members had already found a subtle ripple in the motion of millions of stars that suggested the effects of encountering Sagittarius between 300 and 900 million years ago. Now, using Gaia EDR3, they have uncovered further evidence indicating its strong effects on our galaxy’s star disk.
“The motion patterns in the stars on the disk are different from what we thought,” says Teresa Antoja, University of Barcelona, Spain, who worked on this analysis with colleagues from the DPAC. Although the role of the Sagittarius dwarf galaxy is still debated in some circles, Teresa says, “It could be a good candidate for all of these ailments, as some simulations by other authors show.”
Measurement of 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 extreme data fidelity and the unique potential for limitless scientific breakthroughs.
In one article, Gaia 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, it was measured that the speed of the Solar System changes by 0.23 nm / s every second. Due to this small acceleration, the trajectory of the Solar System is deflected by a diameter of one atom every second, and in a year it reaches about 115 km. The acceleration measured by Gaia shows good agreement with theoretical expectations and provides the first measure of the curvature of the Solar System’s orbit around the galaxy in the history of optical astronomy.
A new stellar census
Gaia EDR3 also made it possible to obtain a new census of the stars in the solar district. The Gaia catalog of nearby stars contains 331 312 objects, which are estimated to be 92% 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 owned only 915 objects, but was upgraded in 1991 to 3803 celestial objects. It was also limited to a distance of 82 light years: Gaia’s census goes four times farther and contains 100 times more stars. It also provides position, motion, and brightness measurements that are orders of magnitude more accurate than old data.
Beyond the Milky Way
A fourth demonstration paper analyzed the Magellanic Clouds: two galaxies that orbit the Milky Way. Having measured the motion of the stars in the Large Magellanic Cloud with greater accuracy than before, Gaia EDR3 clearly shows that the galaxy has a spiral structure. The data also resolves a stream of stars that is extracted from the Small Magellanic Cloud and alludes to previously invisible structures on the periphery of both galaxies.
At 12:00 CET on December 3, the data produced by the numerous scientists and engineers of the Gaia DPAC Consortium becomes public for anyone to watch and learn from. This is the first of a two-part version; the complete Data Release 3 is scheduled for 2022.
“Gaia EDR3 is the result of a huge effort by all involved in the Gaia mission. It’s an extraordinarily rich dataset and I look forward to the many discoveries astronomers around the world will make with this resource, “says Timo Prusti, ESA’s Gaia Project Scientist.” And we’re not done yet; more big data will follow as Gaia continues to make measurements from orbit. “