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The Gaia Space Telescope measured the acceleration of the Solar System as it orbits the center of our galaxy, the Milky Way. The motion of the Solar System with respect to the stars agrees with the results of Finnish astronomers in the 19th century.
Additionally, Gaia’s observational data improves satellite navigation. Finnish researchers are participating in this huge effort, which results in a three-dimensional mapping of our galaxy, to be completed in 2024.
Today, December 3, 2020, the European Space Agency (ESA) released observational data from the Gaia Early Data Release 3 or EDR3, in continuation with the 2016 and 2018 DR1 and DR2 releases. Gaia accumulates accurate data knowledge for example, the stars of the Milky Way, distant extragalactic quasars and asteroids in our Solar System.
Quasars are bright star-like objects that help determine the orientation of planet Earth in space. With the help of their precise positions measured by Gaia, it is possible to construct a new, high-precision reference system to define the positions of stars, Solar System objects and even satellites.
“The knowledge gained by Gaia affects the accuracy of satellite navigation in the future. The positions of the satellites and the orientation of the Earth in space are determined in a reference system linked to the directions of the quasars. The accuracy and state of the art of the system reference points are crucial for accuracy in navigation, “says Professor Markku Poutanen at the Finnish Geospatial Research Institute FGI, National Land Survey of Finland.
Precise observations of quasars have led, for the first time, to a successful calculation of the acceleration of the Solar System.
“The acceleration of the Solar System towards the center of the Milky Way, measured by Gaia, is (2.32 ± 0.16) x 10-10 m / s2 or, approximately, two hundred billionths of the gravitational acceleration caused by the Earth on its surface, “summarizes astronomy professor Karri Muinonen at the Physics Department of the University of Helsinki, also a research professor at the Finnish Geospatial Research Institute FGI.
Gaia in the search for asteroids
Gaia’s data processing is carried out within the European DPAC (Data Processing and Analysis Consortium) network with more than 300 researchers. Solar system researchers from the University of Helsinki take part in Gaia data processing in several ways.
“We are responsible for the daily calculation of orbits for the asteroids discovered by Gaia. Based on these calculations, follow-up observations on the ground are organized,” Muinonen describes.
“Before the data is released, we take part in the validation of Gaia observations of asteroid positions, luminosities and spectra. Our research with Gaia data focuses on asteroid orbits, periods of rotation and polar orientations, masses, the shapes and structural and compositional properties of the surface. In the calculation of collision probabilities for asteroids near the Earth, the precision of the reference systems is completely central “, continues Muinonen.
Gaia’s asteroid observations were published on DR2 in spring 2018 (14099 asteroids). In the next release of DR3 in the spring of 2022, there will be position and brightness data for tens of thousands of asteroids and, for the first time, asteroid spectra will also be released.
Years of work and billions of stars
EDR3 data has been collected by Gaia since the end of July 2014. The data includes, for example, position and brightness data of 1.81 billion stars and color data of 1.55 billion stars over a period of 34 months. Additionally, the data more than triples the number of quasars observed for accurate reference systems to 1.61 million.
EDR3 is a major improvement, both in terms of numbers and accuracy, over previous versions. The latest version provides hints on the gargantuan nature of the upcoming DR3 release in spring 2022 and the final DR4 release after 2024.
Gaia systematically observes astronomical objects at the so-called L2 Lagrange point about 1.5 million kilometers from Earth in an anti-sun direction. Gaia observes about two billion stars with an accuracy, at best, of one hundred millionths of a degree. The result will be a three-dimensional map of our galaxy.
Star motion in the future
Based on the data from Gaia, the researchers modeled the movement of stars in the Milky Way. They produced an animation for the motion of 40,000 randomly selected stars in the sky 1.6 million years into the future.
“In animation, short and long paths describe changes in stellar positions over 80,000 years. The former are mostly related to distant stars, while the latter are solely due to nearby stars. Occasionally, the short paths they expand into long ones and long traces shrink to short ones. This is also related to the changing distances of the stars, “says Muinonen.
At the end of the animation, the stars appear to have been removed from the left and collected on the right. This is due to the movement of the Solar System with respect to the stars. A similar phenomenon can be observed when moving from the center of a wooded islet to its border: the trees in front gradually disappear while they appear to be gathered in the back.
“This shows the mean motion of the Solar System relative to surrounding stars. From the Finnish point of view, it is intriguing that the motion documented by Gaia agrees with the pioneering research on the motion of the Solar System by Friedrich Wilhelm August Argelander (1799 -1875) in the 19th century at the Helsinki Observatory “, concludes Muinonen.
Argelander was the first astronomer, who unequivocally calculated the direction of the movement of the Solar System in space. He worked at the Observatory, the University of Helsinki, then the Imperial Alexander University. He had made observations at the Turku Observatory in 1827-1831 before the observatory moved to Helsinki. In Helsinki he compiled the star catalog entitled “DLX stellarum fixarum positiones mediae ineunte anno 1830” which, as the title says, included the precise positions of 560 stars.
The movement of quasars is actually the movement of the Solar System
More precisely, the apparent stellar streams include information about the movement of the stars and the Solar System over the center of the Milky Way. Observations of the quasar of Gaia allow to determine the acceleration relative to this orbital movement.
Gaia measured the apparent movements of quasars in the sky. These movements are tiny, about one thousandth of the motion of stars 3000 light years away from us. The apparent flow of quasars is directed towards the center of the Milky Way, that is, in the direction in which the acceleration of the Solar System points. Gaia has, in essence, measured the absolute movement of the Solar System with respect to the distant universe. This movement results from the gravitational forces of the Milky Way and all other objects in the universe.
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