KU Leuven: Gaia sees strange stars in most detailed study of the Milky Way yet

Today, ESA’s Gaia mission has opened its treasure trove of new data about our own galaxy. Astronomers, including Professor Conny Aerts from KU Leuven, describe strange ‘starquakes’, stellar DNA, asymmetric movements and other fascinating insights in this most detailed study of the Milky Way yet.

ESA’s Gaia mission aims to create the most accurate and complete multidimensional map of the Milky Way. With this information, astronomers can reconstruct the structure of our galaxy and its evolution over billions of years. It also helps to better understand the life cycle of stars and our place in the universe.

What’s new in dataset 3?
Gaia’s dataset 3 contains new and improved information about nearly two billion stars in our galaxy. The catalog contains new information including chemical compositions, stellar temperatures, colors, masses, ages, and the speed at which stars move toward or away from us (radial velocity). Much of this information came to light through new data obtained through spectroscopy, a technique that splits the starlight (like in a rainbow). This data also includes special subgroups of stars, such as stars that change brightness over time.

Also new to this dataset is the largest catalog to date of binary stars, thousands of solar system objects such as asteroids and planetary moons, and millions of galaxies and quasars beyond the Milky Way.

One of the most surprising discoveries from the new data is that Gaia is able to detect starquakes: tiny movements on the surface of a star that change the shape of stars, something the observatory was not originally built for.

Previously, Gaia discovered radial oscillations that cause stars to swell and shrink periodically, while maintaining their spherical shape. But Gaia has now also spotted other tremors that more closely resemble large-scale tsunamis. These non-radial oscillations change the shape of a star and are therefore more difficult to observe.

Gaia found strong non-radial starquakes among thousands of stars. Gaia also detected such oscillations in stars that had rarely seen this before. These stars, according to current theory, should not have tremors, although Gaia did detect them on their surfaces.

“Starquakes teach us a lot about stars, especially about their internal processes. Gaia opens a gold mine for the ‘asteroseismology’ of massive stars,” says Professor Conny Aerts (KU Leuven), who is part of the Gaia collaboration.

The DNA of stars
What stars are made of can tell us something about their origin and their subsequent journey, and thus about the history of the Milky Way. With the dataset released today, Gaia reveals the largest chemical map of the galaxy linked to 3D motion; from our solar system to smaller galaxies around us.

Some stars contain more ‘heavy metals’ than others. During the Big Bang, only light elements (hydrogen and helium) were formed. All other heavier elements—called “metals” by astronomers—form inside the stars. When stars die, these metals are released and enter the interstellar medium, the gas and dust between the stars from which new stars form. Active star formation and death lead to an environment richer in metals. So a star’s chemical makeup is a bit like its DNA, giving us crucial information about its origin.

Thanks to Gaia, we know that some stars in our galaxy are made of primordial matter, while others, like our sun, are made 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, based on their chemical makeup, that originally came from galaxies other than our own.

“Our galaxy is a beautiful melting pot of stars,” said Alejandra Recio-Blanco of the Observatoire de la Côte d’Azur in France, who is a member of the Gaia collaboration.

“This diversity is extremely important because it tells us the story of how our galaxy was formed. It shows the migration processes within our galaxy and the attraction from external galaxies. It also clearly shows that our sun, and we, are all part of an ever-changing system, formed by the merging of stars and gas of different origin.”

Binary stars, asteroids, quasars, and more
Other articles published today reflect the broad and deep potential of Gaia’s discoveries. A new catalog of binary stars describes the masses and evolution of more than 800 thousand binary systems, while a new survey of asteroids, which includes 156 thousand rocky bodies, digs deeper into the origins of our solar system. Gaia also provides information about 10 million variable stars, mysterious macromolecules between stars, and about quasars and galaxies outside our own cosmic environment.

“Unlike other missions that target specific objects, Gaia is a survey mission. That means that as she scans the entire sky with billions of stars several times, Gaia will inevitably make discoveries that other more specific missions would miss. This is one of its strengths, and we can’t wait for the astronomical community to dive into our new data and learn even more about our galaxy and its environment than we could have imagined,” said Timo Prusti, science project officer for Gaia at ESA.