Monday, June 13, the latest Gaia catalog was unveiled, and with it many new revelations. Among them, an astronomical amount of binary systems has been detailed, showing their number much higher than expected in the galaxy.
The stars are social! Or at least, are born and spend their lives surrounded by other stars, for a third of them. This was revealed by the latest data catalog Gaia Release 3, which listed more than a billion additional objects. Among them are 813,000 double stars that Gaia delivers: two stars in orbit around each other. A high number, especially in comparison with the 300,000 listed so far! In the long term, the mission aims to fully map our Galaxythe Milky Way.
This animation illustrates the movements projected in the sky of binary stars whose orbits were determined by Gaia. Each ellipse corresponds to one of 335 systems located within 50 parsecs (163 light-years) and with periods less than 1,000 days. © ESA, Gaia, DPAC
The orbits are represented on this animation to scale, and are classified by increasing distance from the Sun from top left to bottom right. The white horizontal line in the lower right indicates an apparent size of 10 milliseconds of arc. The color roughly matches the source color as determined by Gaia with purple/blue indicating hot stars and white dwarfsgreen/yellow indicating stars similar to the Sun and red indicating cool, dim stars mass. The movements are equivalent to 1,000 days, duration of observation carried out by Gaïa for this last observation campaign.
It is the influence of one star on the other which makes it possible to identify them.
To obtain all these details, the researchers used the various instruments on board the satellite which make it possible to characterize each targeted object.
When several stars inhabit the same orbit, they influence each other: this is what allows them to be identified. Studied by an outside observer, the multiple systems have a distinctive signature. Their orbit, to begin with, seems out of step with that of a lonely system.
When two objects in orbit are far enough apart, their oscillations in the sky are detected by astrometry, which consists of measuring the position and movement of the stars. In this specific case, one of the two stars is impossible to observe, but the movement of the farthest is enough to deduce its presence. © ESA, Gaia, DPAC
But be careful, if the system is too far from the observer, the two stars will appear merged into one. In the case of a short orbit, of only a few days, the two stars are close: their proximity then gives them a high probability of being observed thanks to the drop in brightness characteristic when passing one in front of the other. Moreover, for these same short-orbit systems, the variations of speed radial can be detected by spectrometry : by study of spectrum light emitted by the source. At the other extreme, very distant multiple systems are detected by the small dip in brightness of faint stars.
Here, spectrometry is used to follow the movement of lines in the light spectrum of stars: if a source approaches then moves away periodically, as in the case of binary systems, its radial velocity also varies periodically. Binaries observed by this method are called spectroscopic binaries. © ESA, Gaia, DPAC
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