Gaia's Massive Third Data Release is out!

It’s here! The third and largest data release (DR3) from the ESA’s Gaia Observatory has officially been made public. As promised, the DR3 contains new and improved details for almost two billion stars in our galaxy, including the chemical compositions, temperatures, colors, masses, ages, and the velocities at which stars move. The release coincided with a virtual press event hosted by the Gaia Data Processing and Analysis Consortium (DPAC) on June 13th, which featured ESA officials and guest speakers who addressed the significance of the new data.

Much of this information consists of newly released spectroscopy data, a technique in which starlight is split into the color spectrum and analyzed to determine how it is being shifted. This technique is known as radial velocity (aka. Doppler Spectroscopy), where light is shifted towards the red or blue end of the spectrum (i.e., redshift and blueshift) based on whether the object is moving towards or away from Earth (respectively). Astrophysicists use this technique to determine how a star is moving relative to our own and also for the sake of detecting exoplanets.

These findings were described in a series of papers released alongside the DR3, which provide an overview of the Gaia mission, the contents of DR3, summarize specifics about the technical details, the processing and calibration of raw data, and the paths taken to arrive at DR3. These papers were published in a special issue of Astronomy & Astrophysics and were made available on the ESA’s website.

The latest release also includes data on special subsets of stars, like those that undergo changes in brightness over time (aka. variable stars). The DR3 also contained the largest catalog of binary star systems, thousands of Solar System objects (asteroids and moons), and millions of galaxies and quasars outside the Solar System (like Andromeda). Other major discoveries include the ability of Gaia to detect tiny motions on the surface of a star (Starquakes) and improved data on the chemical compositions of stars.

Starquakes

As the name suggests, starquakes are a phenomenon where the crust of a star undergoes a sudden adjustment that changes its shape. This was a surprise to astronomers since it is not something the observatory was not originally built for. Previously, Gaia data pointed towards radial oscillations that cause stars to swell and shrink periodically but leave their shape unaffected. The latest data demonstrates that Gaia can also detect nonradial oscillations that are far more powerful but harder to detect because they change the star’s shape globally.

Gaia detected strong nonradial starquakes on the surface of thousands of stars, even where conventional theory states that none should exist. Much like how Earthquakes and similar phenomena on other bodies (like “Moonquakes and “Marsquakes” that have been studied) allow astronomers to learn more about the interior of planets and moons, these starquakes can tell astronomers a great deal about the internal workings of different star types. As the research papers indicate, this information could lead to new opportunities for the field of “asteroseismology.”

Stellar DNA

By studying the chemical composition of stars, astronomers can place tighter constraints on where the stars were born and how they migrated over time. This, in turn, can reveal interesting details about the history of the Milky Way and how it has evolved since. With the DR3, Gaia has revealed the largest chemical map of the galaxy from our solar system to smaller galaxies surrounding the Milky Way. Coupled with proper motion and velocity measurements (astrometry) in the catalog, this information has provided a 3D map of where stars originated and got to where they are today.

The key aspect of stellar composition is the amount of heavy metals they contain, also known as “metallicity.” The first stars in the Universe, which formed roughly 100 million years after the Big Bang, were composed of hydrogen and helium, reflecting the composition of the Universe at the time. These Population III stars (as they’re named) formed heavier elements in their interiors through a slow process of nuclear fusion, where fusion and helium were merged to create boron, carbon, nitrogen, oxygen, silicon, and eventually iron.

When these stars collapsed at the end of their life cycles and exploded in massive supernovae, these elements were dispersed through the interstellar medium (ISM) – from which new stars formed. This active cycle of star formation and death slowly enriched the interstellar medium with metals over time. Subsequent generations of stars, known as Population II and I, contained greater and greater amounts of these elements, which can be used to determine their age. In this respect, a star’s chemical composition is like its DNA since it can yield crucial information about its origin.

With this latest release, Gaia has revealed that some stars in our galaxy are “metal-poor” and composed of primordial material, while others (like our Sun) are rich in metal. The data also showed that stars closer to the center and plane of our galaxy have higher metallicities than those farther from the center and outside the galactic disk. Based on their compositions, Gaia also identified numerous stars that formed in different galaxies but were captured by the Milky Way or became part of it through galactic mergers.

Alejandra Recio-Blanco, an astronomer with the Observatoire de la Côte d’Azur and a member of the Gaia Collaboration, explained:

“Our galaxy is a beautiful melting pot of stars. This diversity is extremely important, because it tells us the story of our galaxy’s formation. It reveals the processes of migration within our galaxy and accretion from external galaxies. It also clearly shows that our Sun, and we, all belong to an ever changing system, formed thanks to the assembly of stars and gas of different origins.”

Other Findings

Other research papers that were released alongside the DR3 describe numerous other discoveries, which demonstrate the sheer potential of the Gaia mission. In particular, the new binary star catalog (the largest ever) contains data on the mass and evolution of more than 800,000 binary systems. Another breakthrough is a new asteroid survey that provides data on the origins of 156,000 thousand rocky bodies in our Solar System. Lastly, Gaia‘s observations have revealed about 10 million variable stars, macro-molecules in the ISM, and quasars and galaxies. Said Timo Prusti, Gaia Project Scientist at the ESA:

“Unlike other missions that target specific objects, Gaia is a survey mission. This means that while surveying the entire sky with billions of stars multiple times, Gaia is bound to make discoveries that other more dedicated missions would miss. This is one of its strengths, and we can’t wait for the astronomy community to dive into our new data to find out even more about our galaxy and its surroundings than we could’ve imagined.”

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Additional releases are planned, the date of which will depend on future mission extensions. The mission has been approved until the end of 2022, and there are indications that it will be extended further to 2025. In the event of this, the full data release for the five-year nominal mission (DR4) will take place before the extended mission wraps up, and DR5 – which will contain data from the full ten-year run – will be released no earlier than three years after the end of the mission.

This final product will contain the most precise astronomical measurements ever made and will include:

• Full astrometric, photometric, and radial-velocity catalogs
• All available variable-star and non-single-star solutions
• Source classifications (probabilities) plus multiple astrophysical parameters (derived from BP/RP, RVS, and astrometry) for stars, unresolved binaries, galaxies, and quasars. Some parameters may not be available for faint(er) stars
• An exo-planet list
• All epoch and transit data for all sources

All of this information will be made available for free to researchers and the general public through the ESA’s Gaia Data Release Schedule. The Gaia Data Processing and Analysis Consortium‘s public outreach working group is also collaborating with the Astronomical Calculation Institute (ARI) at Heidelberg University to develop Gaia Sky – been developed to explore the galaxy in three dimensions using Gaia data.

Further Reading: ESA