In Research
Photo : @Spacecraft: ESA/ATG medialab; Milky Way: ESA/Gaia/DPAC; CC BY-SA 3.0 IGO. Acknowledgement: A. Moitinho.

On 13 June, the European Space Agency (ESA) published the new Gaia catalogue, which is the largest, most detailed and most accurate catalogue of the Milky Way to date. This third release of data from the Gaia satellite contains an enormous amount of information about the stars and celestial objects that make up our Galaxy.

With more than 1.8 billion objects observed, the release of the Gaia catalogue is one of the most eagerly awaited events in the astronomical community and promises significant scientific benefits.

Belgian astronomers contributed to the Europe-wide consortium that makes this catalogue available. The survey will allow us to discover new asteroids, binary stars and “starquakes” and shed new insights into our Milky Way Galaxy.

Gaia s chemical map of the Milky Way

A sample of Milky Way stars in the Gaia data version 3. The colour indicates the stellar metallicity. Redder stars are richer in metals.

The Gaia satellite has been charting the sky since 2014, and its map includes stars that are a million times fainter than can be seen with the naked eye. Gaia has measured exceptionally accurate distances to almost 2 billion stars, and has measured how fast and in which direction the stars move through space as they orbit the centre of our Milky Way.

The third data release of Gaia adds a completely new dimension to these previous results. Using the spectroscopic information that Gaia collected, astronomers have determined stellar temperatures, masses, and ages of these stars. Also the speed at which stars move towards or away from us was determined, as well as their chemical composition. Detailed information about stars that vary in brightness over time or starquakes, or stars that are part of a binary system, is a further important part of the data release. It does not stop there, because Gaia also sees objects much closer by than the Milky Way stars, such as asteroids in the Solar System. Much further away, it has observed millions of galaxies and quasars outside our Milky Way.

The specialised expertise of Belgian researchers played an important role in the Europe-wide consortium that analysed the enormous amount of Gaia data. Astronomers from KU Leuven, the Royal Observatory of Belgium, ULB, Universiteit Antwerpen and University of Liège (ULiège) all contributed to this work. The Belgian participation to the Gaia mission has been made possible through funding provided by the Belgian Federal Science Policy (BELSPO) via the PRODEX Programme of ESA.

Ludovic Delchambre, astrophysicist, researcher at the STAR institute (Space sciences, Technologies and Astrophysics Research) explains the role of ULiège in the analysis of the data provided by Gaia.

“Researchers from the STAR institute at ULiège have a well-established expertise in the determination of the orbital parameters of binary stellar systems based on their observed radial velocities. From the Doppler effect induced by the back and forth motion of stars orbiting around each other, Gaia can measure the apparent velocities of one or both of their constituting components. The repeated measurements of these radial velocities over time are then subsequently used in order to derive the mass ratio, the period, the inclination and the eccentricity of the systems. Around 200 000 binary stars were thereby detected and characterised in Gaia DR3 by the ULiège team.”

“Our researchers are also involved in the determination of the redshifts and distances of extremely bright extragalactic sources that are quasars. Owing to the expansion of the Universe, the wavelength of the light emitted by such objects undergoes a stretching during its travel through the cosmos. This effect, called redshift, makes the quasar appear redder than when its light was initially emitted, billions of years ago. More than 6 million quasar candidates will have their redshift published in Gaia DR3 and will provide an indirect measure of their distances.”

Mission GAIA


Ludovic Delchambre

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