# 19.4 Stellar multiplicity – A teaser for the hidden treasure

Understanding the statistical properties of binary and multiple stars is one important ingredient for the knowledge of our Galaxy, and the distribution of the companion properties down to the substellar regime is another key for the understanding of stellar formation and evolution. As a huge survey collecting astrometric, photometric, and spectroscopic complementary data, Gaia DR3 with its non-single star tables brings a revolutionary new view of these fundamental subjects.

Gaia Collaboration et al. (2022a) illustrates what can readily be inferred about the binarity from extrasolar planets to massive compact companions. For this purpose, table binary_masses is published. Its purpose is to provide an estimation of the masses of components, or at least lower or upper limits, computed using the orbital parameters from the nss_two_body_orbit table in the Gaia ESA Archive together with photometric information.

The description of the table content is given in Gaia Collaboration et al. (2022a), Sect. 5. For a limited number of solutions, the mass of the two components and their flux ratio, together with the associated $\pm 1\sigma$ confidence intervals, are provided. For most solutions, however, part of this information only is given, depending on the kind of non-single star solution that is published. For this purpose, a field shows which combination method has been used, and a flag indicates how the primary mass was computed, in particular whether a method deriving a mass consistent with the flux ratio has been used. Another flag indicates whether it is suspected that the companion may be a compact object.