Astronomers from the Gaia Data Processing and Analysis Consortium released today the most detailed ever catalogue of Milky Way stars. The new data set, called the Gaia Early Data Release 3 (EDR3), contains detailed information — stellar positions, movement, brightness and colors — on more than 1.8 billion sources, detected by ESA’s Gaia satellite. This represents an increase of more than 100 million sources over the previous data release, which was made public in April 2018.
Data from more than 1.8 billion stars have been used to create this map of the entire sky. It shows the total brightness and color of stars observed by ESA’s Gaia satellite and released as part of Gaia’s Early Data Release 3. Brighter regions represent denser concentrations of bright stars, while darker 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 patch of the sky. The bright horizontal structure that dominates the image is the plane of our Milky Way Galaxy. It is actually a flattened disk seen edge-on that contains most of the Galaxy’s stars. In the middle of the image, the Galactic center appears bright, and thronged with stars. Darker regions across the Galactic plane correspond to foreground clouds of interstellar gas and dust, which absorb the light of more distant stars. Many of these clouds conceal stellar nurseries where new generations of stars are currently being born. Dotted across the image are also many globular and open clusters, as well as entire galaxies beyond our own. The two bright objects in the lower right of the image are the Large and Small Magellanic Clouds, two dwarf galaxies orbiting the Milky Way. Image credit: ESA / Gaia / DPAC / CC BY-SA 3.0 IGO / A. Moitinho.
Launched on December 19, 2013, Gaia operates in an orbit around the so-called Lagrange 2 (L2) point, located 1.5 million km behind the Earth in the direction away from the Sun.
At L2 the gravitational forces between the Earth and Sun are balanced, so the spacecraft stays in a stable position, allowing long-term essentially unobstructed views of the sky.
The primary objective of Gaia is measure stellar distances using the parallax method.
In this case, astronomers use the observatory to continuously scan the sky, measuring the apparent change in the positions of stars over time, resulting from the Earth’s movement around the Sun. Knowing that tiny shift in the positions of stars allows their distances to be calculated.
Gaia also tracks the changing brightness and positions of the stars over time across the line of sight (their so-called proper motion), and by splitting their light into spectra, measures how fast they are moving towards or away from the Sun and assesses their chemical composition.
Equipped with 106 CCDs forming the equivalent of a camera with a resolution of a billion pixels, Gaia surveys 50 million stars per day, each time carrying out ten measurements, which represents a total of 500 million data points per day.
“Gaia is measuring the distances of hundreds of millions of objects that are many thousands of light years away, at an accuracy equivalent to measuring the thickness of hair at a distance of more than 2,000 km,” said UK Gaia DPAC project manager Dr. Floor van Leeuwen, an astronomer in the Institute of Astronomy at the University of Cambridge.
“These data are one of the backbones of astrophysics, allowing us to forensically analyze our stellar neighborhood, and tackle crucial questions about the origin and future of our Galaxy.”
Two previous releases — Gaia DR1 and Gaia DR2 — included the positions of 1.6 billion stars.
The Gaia EDR3 release brings the total to just under 2 billion stars, whose positions are significantly more accurate than in the earlier data. This is the first of a two-part release; the full Gaia DR3 release is planned for 2022.
“The new Gaia data promise to be a treasure trove for astronomers,” said Gaia deputy project scientist Dr. Jos de Bruijne, an astronomer at ESA.
The new data include exceptionally accurate measurements of 331,312 objects — about 92% of the stars within 100 parsecs (326 light-years) of the Sun.
The previous census of the solar neighborhood, called the Gliese Catalogue of Nearby stars, was carried out in 1957. It possessed just 915 objects initially, but was updated in 1991 to 3,803 celestial objects.
It was also limited to a distance of 82 light years: Gaia’s census reaches four times farther and contains 100 times more stars. It also provides location, motion, and brightness measurements that are orders of magnitude more precise than the old data.
The researchers also confirm that the Solar System is accelerating in its orbit around the Galaxy.
Using the observed motions of extremely distant galaxies, the velocity of our Solar System has been measured to change by 0.23 nm/s every second.
Because of this tiny acceleration, the trajectory of the Solar System is deflected by the diameter of an atom every second, and in a year this adds up to around 115 km.
The acceleration measured by Gaia shows a good agreement with the 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.
The team also sees the evidence of the Milky Way’s past by looking at stars in the direction of the Galaxy’s ‘anticenter’. This is in the exact opposite direction on the sky from the center of the Galaxy.
Computer models predicted that the disk of the Milky Way will grow larger with time as new stars are born.
The new data allow the scientists to see the relics of the 10 billion-year-old ancient disk and so determine its smaller extent compared to the Milky Way’s current disk size.
The data from these outer regions also strengthen the evidence for another major event in the more recent past of the Galaxy.
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 that are heading downwards towards the plane, and a component of fast-moving stars below the plane that are moving upwards.
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 more recent past.
“The patterns of movement in the disk stars are different to what we used to believe,” said Dr. Teresa Antoja, an astronomer at the University of Barcelona.
“Although the role of the Sagittarius dwarf galaxy is still debated in some quarters, it could be a good candidate for all these disturbances, as some simulations from other authors show.”
The new Gaia data additionally deconstruct the two largest companion galaxies to the Milky Way, the Small and Large Magellanic Clouds, allowing the astronomers to see their different stellar populations.
Having measured the movement of the Large Magellanic Cloud’s stars to greater precision than before, the team clearly shows that the galaxy has a spiral structure.
The data also resolve a stream of stars that is being pulled out of the Small Magellanic Cloud, and hints at previously unseen structures in the outskirts of both galaxies.
“Gaia EDR3 is the result of a huge effort from everyone involved in the Gaia mission,” said Gaia project scientist Dr. Timo Prusti, an astronomer at ESA.
“It’s an extraordinarily rich data set, and I look forward to the many discoveries that astronomers from around the world will make with this resource.”
“And we’re not done yet; more great data will follow as Gaia continues to make measurements from orbit.”
These fascinating results come from a set of papers that demonstrate the quality of the EDR3 release.
