Climate zones, soil types, land use – geoscientists love to immerse themselves in thematic maps. Astronomers now also have this pleasure thanks to “Gaia”. The Milky Way has been mapped in 3D with a telescope on board the spacecraft since 2014.
The mission’s largest data package to date was released on Monday. It is far more than a map: a comprehensive atlas of our home galaxy.
The atlas is based on position and brightness data from around 1.8 billion objects, mostly stars, that were published two years ago. More details are now available, such as chemical compositions, stellar temperatures, colors, masses, ages, and the speeds at which stars are moving toward or away from us. This makes it possible to find out which ones have been circling around the black hole in the center of the Milky Way for a long time and which ones were formed in other galaxies and came to us.
The European space agency Esa also provides a catalog that is intended to provide information about the mass and the development of more than 800,000 binary star systems. It has also captured tens of thousands of asteroids, more than ten million variable stars, black holes called quasars, and galaxies outside of our own cosmic neighborhood.
The researchers owe much of the new data to spectroscopy. In this process, starlight is split into its individual colors. This creates a kind of individual fingerprints of the celestial bodies. The spectra depend, among other things, on the chemical composition and the movement of the celestial bodies relative to the observer.
“Using this data, we can understand the development history of the Milky Way,” says Roelof de Jong from the Leibniz Institute for Astrophysics in Potsdam (AIP), which is significantly involved in the Gaia mission. After the Big Bang there was initially only hydrogen and helium, heavy elements were formed inside stars and thrown into intergalactic space by supernovae. Stars of later generations formed from the dust.
“Depending on the original material of which today’s stars are made, they have different numbers of heavy elements,” explains the researcher. Based on the Gaia data, different groups of objects can be identified, some of which come from other galaxies and have migrated into the Milky Way.
The light from the stars is often very weak and the devices work at the limit of what can be measured. There are also disruptions. This is how it turned out after the telescope was launched: Individual fibers protrude from the foldable shield that shields it from sunlight. “These partially direct the sunlight into the sensitive optics,” explains de Jong. The problem was solved with software developed at the AIP.
There were also positive surprises. Although not specifically designed for this purpose, Gaia proved to be a sensitive instrument for detecting starquakes. These are recurring surface changes that vary greatly by star and also occur in the Sun. “Just as seismologists use earthquakes to explore the interiors of planets, stellar tremors can help us learn more about the temperature, density and rotation inside stars,” said Conny Aerts of the University of Leuven in Belgium, presenting the results.
The observatory has tracked down more than 100,000 stars that “buzz” in this way. The most promising ones are to be observed from 2026 by the Esa probe “Plato”, which specializes in stellar seismology. “The measurements of Gaia and Plato are a veritable gold mine to study these phenomena.”
The data from the current mission could also help to track down the mysterious dark matter. So far nobody can say exactly what it consists of. But it is very likely that they exist. The movement of stars and galaxies is determined by gravity – and cannot be explained solely with that of visible matter. So there must be more.
“When a dwarf galaxy enters the Milky Way, it is stretched by galactic tidal forces,” says de Jong. But the movement of the stars is complex, something invisible is pulling them. Dark matter? “We don’t know,” says the AIP researcher. “But with the precise measurements from Gaia, we can for the first time test suspected dark matter effects on smaller scales.”
According to de Jong, the data available so far may not be sufficient. But more are in sight: the mission has already been extended several times beyond the original operating period of five years. The telescope is still intact and continues the measurements.
The scientific yield is already enormous. On average, five specialist articles based on Gaia data have been published every day since 2020, said Günther Hasinger, Director of Science at Esa. “We have already overtaken the previous gold standard, the Hubble telescope.”