ESA's Gaia mission presents the Milky Way in motion

Version 3 of data from ESA’s Gaia mission shows the speed at which more than 30 million objects in the Milky Way (mainly stars) are approaching or receding from us.

This is called ‘radial speed’. Now we can see how objects move over a large part of the Milky Way’s disk, explains ESA in a statement published on the occasion of the publication of the new mission database on June 13.

The rotation of the disk, projected along the line of sight (top left image), is visible by alternating bright areas (facing away from us) and dark areas (facing toward us). Various objects whose radial velocity differs from that of their near surroundings are visible by contrast.

The Large and Small Magellanic Clouds (LMC and SMC) appear as bright spots in the lower right corner of the image. The Sagittarius Dwarf Galaxy is visible as a faint nearly vertical stripe below the Galactic Center. Several globular clusters appear as small dots in the image, such as 47 Tucanae, the dark dot to the immediate left of the SMC.

The sky map (lower left image) shows the Milky Way’s velocity field for about 26 million stars. The colors show the radial velocities of the stars along the line of sight. Blue shows the parts of the sky where the average motion of the stars is toward us, and red shows the regions where the average motion is away from us. The visible lines in the figure trace the motion of the stars projected on the sky (proper motion). These lines show how the direction of the stars’ velocity varies with galactic latitude and longitude. The Large and Small Magellanic Clouds (LMC and SMC) are not visible as only stars with well defined distances were selected to make this image.

Gaia doesn’t just map the stars in our galaxy, she tells us what’s between the stars. The space between stars is not empty, but is filled with clouds of dust and gas, from which stars are born.

Through precise measurements of the positions of stars and their scattered light, Gaia allows us to map the absorption of starlight by the interstellar medium. Those maps give us essential clues about the physical mechanisms of star formation, galaxies, and the history of our home galaxy.

This map (upper right image) shows the interstellar dust that fills the Milky Way. The dark regions in the center of the galactic plane in black are the regions with a large amount of interstellar dust that fades to yellow as the amount of dust decreases.

What stars are made of can tell us about their birthplace and subsequent journey, and thus about the history of the Milky Way. With the new data release, Gaia brings us a chemical map of the galaxy (lower right image).

With Gaia, we see that some stars in our galaxy are made of primordial material, while others, like our Sun, are made of matter enriched by earlier generations of stars. Stars that are closer to the center and plane of our galaxy are richer in metals than stars that are further away.

This all-sky view shows a sample of the Milky Way’s stars in Gaia Data Release 3. Color indicates stellar metallicity. The reddest stars are rich in metals.

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