The Gaia Space Telescope has been scanning the Milky Way with unprecedented precision since 2013. Astronomers have now published the third and most extensive map of our home galaxy to date. The data set contains the positions and movements of around 1.8 billion stars – more than ever recorded before. At the same time, the space telescope also provides new information about stars in the vicinity of our sun, the outer areas of the Milky Way and the Magellanic Clouds. Even subtle changes in the motion of our solar system reveal the new data.
The Gaia space telescope, developed and operated by the European Space Agency ESA, has been orbiting around Lagrangian point L2 since 2013 – a point that is around 1.5 million kilometers behind the earth when viewed from the sun. There, the forces of attraction of the celestial bodies are in balance so that a stable, economical path with an uninterrupted view of the starry sky is possible. The Gaia Observatory measures the distance, spectrum and movement of stars in the Milky Way using several mirror telescopes, CCD sensors and spectrometers. All stars come into the observation area of the telescope several times. Gaia observes an average of 850 million objects per day and collects around 20 gigabytes of data. Overall, the mission’s goal is to map around two billion celestial bodies in the Milky Way.
The three-dimensional star catalog resulting from this data offers decisive insights into the history of our home galaxy, but also into how it will change in the future. “The first two Gaia catalogs were published in September 2016 and April 2018 and have already had a lasting impact on our image of the development of the Milky Way,” explains Alessandra Roy, Gaia project manager at the German Aerospace Center (DLR). At the same time, the data also provide information about the development of stars and star remnants. The second catalog made it possible to check and refine the so-called Hertzsprung-Russell diagram. This diagram shows how the star features change in the course of their life and forms the basis for the classification of the different types of stars.
Insights into old collisions and current neighbors
Now astronomers have published the third Gaia dataset. With around 1.8 billion celestial bodies, it comprises around 100 million objects more than before. In addition, it maps the movement and the spectrum of 1.5 billion stars – this makes it possible to draw conclusions about the origin and age of various star currents and populations in the Milky Way even better and more precisely than before. The new data show that above the main plane of our galaxy there is a stream of slower stars wandering towards the center. On the other hand, below the galactic level, a faster stream of stars moves upwards. Astronomers suspect that these newly identified star streams are relics of an ancient near-collision between our galaxy and the neighboring Sagittarius dwarf galaxy. It is known from previous observations that this little neighbor of the Milky Way has already wandered through its fringes several times.
Also new in the third data set is a closer look at the stars in the vicinity of our solar system. For a long time, only objects within a radius of less than 100 light years were more precisely recorded and mapped. The new Gaia catalog now lists the properties and positions of more than 330,000 stars within 326 light years of our sun – this corresponds to around 92 percent of all objects in this area. At the same time, Gaia has also directed his gaze into the outer areas of our home galaxy and even beyond. The new catalog shows the movements of stars in the two magellanic clouds and two dwarf galaxies 160,000 and 200,000 light years away, respectively. These data reveal, among other things, that the Large Magellanic Cloud has a spiral structure despite its irregular, diffuse-appearing shape.
The solar system is getting faster
The Gaia catalog also provides new information about our solar system. Because from the movement of the stars around us, astronomers can also deduce the path and speed at which our home star is moving around the center of the Milky Way. According to this, the solar system experiences a slight acceleration over time, its speed changes every second by 0.23 nanometers per second – this corresponds to a deviation of one atomic diameter per second. In the year this adds up to an acceleration that advances our solar system around 115 kilometers further than in the year before.
(Video: European Space Agency (ESA))
“The new Gaia catalog already promises to become a real treasure trove for astronomers,” says Jos de Bruijne from ESA. The astronomer Floor van Leeuwen from the University of Cambridge adds: “These data form one of the pillars of astrophysics, because they allow us to examine our stellar neighborhood and to clarify crucial questions about the origin and the future of our galaxy.” The story of Gaia continues: Originally, the end of the Gaia mission was planned for 2019. Since all the instruments on board the satellite are still fully functional, the probe is supposed to collect data until 2025 – by then the gas supplies on board used to align the satellite will probably be completely used up. Further, even more complete publications of the Gaia catalog are planned from 2022.
Source: ESA / German Aerospace Center (DLR)