Gaia is ESA’s mission to create the most accurate and comprehensive multidimensional map of the Milky Way. This allows astronomers to reconstruct the structure of our original galaxy and its past evolution over billions of years, and to better understand the life cycle of stars and our place in the Universe.
For the first time, Gaia’s latest data release, Data Release 3, contains star chemistry, measured from high-resolution spectroscopy, a technique in which starlight is split into its constituent colors (like a Rainbow).
The data reveals what six million stars are made of, as well as how fast 35 million stars are moving towards or away from us (the radial velocity). This multiplies the number of radial velocities listed by five.
Professor Mark Cropper (UCL Mullard Space Science Laboratory), who played a key role in the development of Gaia’s Radial Velocity Spectrometer (RVS), said: “This is by far the largest catalog of radial velocities, reaching the center of the Milky Way, and in its halo.
“For the first time, this covers enough of the Milky Way to unveil its formation history and to understand the behavior of its spiral arms and central bar. A next step will be to compare these 3D movements and positions to advanced computer simulations.
ESA’s Gaia 3 data release shows us how fast more than 30 million Milky Way objects (mostly stars) are approaching or moving away from us.
The DNA of stars
Dr George Seabroke (UCL Mullard Space Science Laboratory) said: “Chemical mapping of Gaia is analogous to DNA sequencing of the human genome. The more we know about the chemistry of stars, the better we can understand our galaxy as a whole. Gaia’s chemical catalog of six million stars is ten times larger than previous terrestrial catalogs, so it’s truly groundbreaking. Data releases from Gaia tell us where the stars were and how they move. Now we also know what many of these stars are made of.
View of the whole sky in galactic coordinates (HEALPix map) showing the stars in the Gaia DR3 GSP-Spec database (Gaia Collaboration, Recio-Blanco et al. 2022). The color indicates stellar metallicity, [M/H]it is the average abundance of all chemical elements
Some stars contain more “heavy metals” than others. During the Big Bang, only light elements were formed (hydrogen and helium). All other heavier elements – called metals by astronomers – are built inside stars. When stars die, they release these metals into the gas and dust between stars called the interstellar medium, from which new stars are formed. The formation and death of active stars will lead to a more metal-rich environment. Therefore, a star’s chemical composition somewhat resembles its DNA, giving us crucial information about its origin.
With Gaia, we see that some stars in our galaxy are made up of primordial matter, while others like our Sun are made up of matter enriched by previous generations of stars. Stars closer to the center and plane of our galaxy are richer in metals than stars at greater distances. Gaia has also identified stars originally from galaxies different from ours, based on their chemical composition.
Starquakes, binary stars, asteroids, quasars, etc.
The data also includes special subsets of stars, such as those that change brightness over time. Along with chemical compositions and radial velocities, the catalog includes new information on the temperatures, colors, masses, and ages of stars.
One of the most startling discoveries from the new data is that Gaia is able to detect starquakes – tiny movements on a star’s surface – that change the shape of stars, something the observatory does for n was not originally designed.
Previously, Gaia had found radial oscillations that cause stars to periodically swell and shrink, while retaining their spherical shape. But Gaia has also spotted other vibrations that are more like large-scale tsunamis. These non-radial oscillations change the overall shape of a star and are therefore more difficult to detect.
Other papers published today reflect the breadth and depth of Gaia’s discovery potential. A new catalog of binary stars presents the mass and evolution of more than 800,000 binary systems, while a new study of asteroids including 156,000 rocky bodies digs deeper into the origin of our solar system. Gaia also reveals information about 10 million variable stars, mysterious macromolecules between stars, as well as quasars and galaxies beyond our own cosmic neighborhood.
UCL Mullard Space Science Laboratory has contributed significantly to Gaia for 21 years by developing Gaia spectrometer concepts, testing and calibrating each of the 106 electronic detectors used to capture all Gaia data, and playing a major role in the processing of spectroscopic data – MSSL is responsible for the development of the software that calibrated the RVS instrument which allows to extract, calibrate and combine the RVS spectra into an average spectrum per star. One million of these combined spectra are first published in Data Release 3 and they have been used to derive the chemistries of nearly six million stars.
The UK team involved in the Gaia mission is supported by the UK Space Agency and the Science and Technology Facilities Council.