Top: the two stars in real physical space. Colors show their common gravitational field; the grey shaped region around them approximately indicate the Roche-lobe (i.e. the closermost common gravitational equipotential surface). If one of the stars puffs up to fill the Roche-lobe, its mass starts to flow towards the companion. Bottom left: Hertzsprung--Russell diagram of both binary companions. Bottom right: time evolution of the radial distance between the two stars (with the center of mass at zero). When the contact phase happens at 3.1775~Myr, the orbit quickly changes due to the change in relative masses: the mass gainer (the secondary) moves closer to the center of mass, while the mass donor (the primary) moves away from it. The underlying data for this animation was kindly provided by Athira Menon; the binary model was computed by her with the MESA code. The animation was designed and rendered by Dorottya Szécsi who works as a research fellow and a stellar evolution expert associated with Prof. Walch-Gassner's group.
Binary stars in touch
Dr. Dorottya Szécsi
One thing that has an important contribution on star-formation through their strong feedback, is massive stars. However, massive stars' life is complicated by, amongst other things, the fact that many of them are born close to another one! We call these double stars binaries.
About 50% of all massive stars are born in binaries (Sana et al. 2012). And if they do, their life is fundamentally changed. Indeed, the companions can influence each other for example by... stealing each other's material!(Götberg et al. 2019) Let's see how.
In this video, the coupled life of a binary star system is shown. These two stars come `in touch' for a short time around 3.1775~Myr. This is called the contact phase during which the stars exchange mass between them very rapidly. This mass exchange leads to a change in orbit, as well as to a change in both of their luminosities and surface temperatures.
And if so, this should be taken into account when determining the feedback of massive stellar populations. Indeed, binary interaction typically leads to more blue (i.e. hot) populations (de Mink et al. 2014) -- therefore, for a realistic treatment of stellar feedback, we need to switch from synthetic single star populations to synthetic binary populations in star-formation simulations. This is something we are working on right now. Stay tuned!