Astronomers have mapped the stars on the very anticenter of the Milky Way

The most accurate three-dimensional map of the Milky Way to date reveals the secrets of our galaxy. Looking deep into the anticenter – the opposite direction from the galactic center – helps astronomers piece together the Milky Way’s wild past.

The European Space Agency’s Gaia satellite, launched in 2013, has been working for years to map the galaxy in as much detail and with the highest precision possible. Its new data release, Gaia Early Data Release 3 (EDR3), is a huge improvement over existing data, as demonstrated by a series of new papers published in Astronomy and astrophysics.

In addition to probing the galaxy’s anticenter, astronomers have described the solar system’s orbit around the galactic center, taken a closer look at the Magellanic clouds that orbit the Milky Way, and taken the largest census in this day of the stars of the Milky Way and their movement in the sky.

“The new data from Gaia promises to be a treasure trove for astronomers,” said ESA astronomer Jos de Bruijne.

Gaia revolves around the Sun with Earth, in a looping orbit around the Sun-Earth Lagrangian point L2, a gravitationally stable pocket of space created by the interactions between the two bodies. From there, he carefully studies the stars of the Milky Way over an extended period of time, observing how the positions of the stars appear to change relative to more distant stars. This provides a parallax, which can be used to calculate distances to stars.

It can be done from here on Earth, but atmospheric effects can interfere with measurements. Due to his position in space, Gaia has an advantage, which he uses wisely.

To date, it has mapped 1.8 billion sources in detail and collected color information on 1.5 billion sources. According to ESA, this represents an increase of 100 million and 200 million sources compared to Data Release 2 in 2018.

Of particular interest is the Milky Way’s anticenter. This region is not as densely populated as the galactic center, nor as obscured by interstellar clouds of thick dust, giving a clearer view of the stars on the edge of the Milky Way.

(ESA / Hubble, sketch: ESA / Gaia / DPAC)

This region shows more clearly the disruption inflicted on the Milky Way throughout its history and, studying the new data, astronomers have concluded that the galaxy’s disk was once smaller than it is today. .

Interestingly, the older stars – the original population of the Milky Way – don’t extend as far as the stars of the sausage Gaia, a galaxy that merged with the Milky Way 8-10 billion years ago. ‘years.

Looking above and below the galactic plane, a different picture emerges. A group of stars above the plane moves downward and stars below move upward. This, according to the analysis, could be the result of a slow and continuous collision with the dwarf galaxy of Sagittarius, ruffling the outer edge of the Milky Way’s disk.

The Sagittarius galaxy, according to an article published earlier this year based on Gaia DR2, is likely distorting the Milky Way’s disk as it moves. Its last close encounter is difficult to say, but it took place between 300 and 900 million years ago, producing strong disturbances.

While unexpected, the eerie motions of the stars spotted in EDR3 could be further evidence of the ongoing interaction between the two galaxies, as determined by simulations that match the observations.

View of Gaia on the Magellanic Clouds. (ESA / Gaia / DPAC; CC BY-SA 3.0 IGO)

It’s not the only violence Gaia has confirmed. The Milky Way has two companions, the Large and Small Magellanic Clouds, orbiting each other as they also move around the Milky Way. Eventually these will also merge into the Milky Way, but they are also engaged in interactions with each other.

In Gaia’s data, astronomers observed in more detail a flow of stars called the Magellanic Bridge being withdrawn from the Small Magellanic Cloud to the Large Magellanic Cloud. They also clearly observed the spiraling structure of the Large Magellanic Cloud, and found enticing hints of previously invisible structures on the outer edges of the two Clouds.

The movement of the solar system has also been slightly revised. By observing the movements of distant galaxies, astronomers have been able to calculate the acceleration of the solar system relative to the resting frame of the Universe. This gave us the first measurement of the curvature of the solar system’s orbit around the center of the Milky Way.

And a new census of stars within 100 parsecs (326 light years) of the solar system is the most complete yet. It contains 331,312 stars – about 92% of all stars within this distance. The Gaia Catalog of Nearby Stars should provide an invaluable reference for astronomy.

Based on previous Gaia data releases, we’ve learned a lot about our home galaxy, including some fascinating surprises, such as the Milky Way’s largest gas structure, hidden stellar flows from ancient collisions, and a new estimate of the size of the Milky Way (it was much bigger than we thought!).

EDR3 will deepen this knowledge and Gaia, although near the end of her mission, is not yet complete. EDR3 is only the first part of the data release. The second part arrives in 2022.

The satellite will also retire in 2022. But it will do so after irrevocably changing astronomy and our understanding of the space around us.

The articles were published in Astronomy and astrophysics, and the publication of the data can be found here.