Den galax som jorden och solen befinner sig i, Vintergatan, ska nu kartläggas noggrannare av en ny satellit, Gaia, som snart ska skjutas upp av European Space Agency (ESA) från den europeiska rymdbasen i Franska Guayana. Minst en miljard av Vintergatans stjärnor ska undersökas och mätas:
Gaia will create an extraordinarily precise three-dimensional map of more than a thousand million stars throughout our Galaxy and beyond, mapping their motions, luminosity, temperature and composition. This huge stellar census will provide the data needed to tackle an enormous range of important problems related to the origin, structure and evolutionary history of our Galaxy.
For example, Gaia will identify which stars are relics from smaller galaxies long ago ‘swallowed’ by the Milky Way. By watching for the large-scale motion of stars in our Galaxy, it will also probe the distribution of dark matter, the invisible substance thought to hold our Galaxy together.
Gaia will achieve its goals by repeatedly measuring the positions of all objects down to magnitude 20 (about 400 000 times fainter than can be seen with the naked eye).
For all objects brighter than magnitude 15 (4000 times fainter than the naked eye limit), Gaia will measure their positions to an accuracy of 24 microarcseconds. This is comparable to measuring the diameter of a human hair at a distance of 1000 km.
It will allow the nearest stars to have their distances measured to the extraordinary accuracy of 0.001%. Even stars near the Galactic centre, some 30 000 light-years away, will have their distances measured to within an accuracy of 20%.
The vast catalogue of celestial objects expected from Gaia’s scientific haul will not only benefit studies of our own Solar System and Galaxy, but also the fundamental physics that underpins our entire Universe.
Det är första gången något sådant här ska göras. Ingen har tidigare så noggrant kartlagt Vintergatan och dess stjärnor.