How stars lose their partners

About half of the stars are accompanied by partners and sail through space in double systems while others move alone. Why do couples break up immediately after leaving the birth area? 

How stars lose their partners
About half of the stars are accompanied by partners and sail through space in double systems while others move alone. Why do couples break up immediately after leaving the birth area?

The open cluster NGC 265 as imaged by the Hubble Space Telescope
Not all planets are lonely like our sun. In our galaxy, the Milky Way, about half of the stars are accompanied by partners, sailing through space in double systems. But the reason why some stars move in double and triple systems while others move alone is still a mystery. Now a team of astronomers from the University of Bonn and the Max Planck Institute for Radio Astronomy (also in Bonn) believe they have discovered the answer - different environments of star birth determine whether a star will have a partner.
The scientists published their paper in the September issue of the journal Monthly Notices of the Royal Astronomical Society.

Stars usually do not form in isolation but in groups within clouds of gas and dust or nebulae. These star factories usually form double systems. This means that almost all birth stars come in pairs. Most groups quickly disperse so that their members become part of the galaxy. Why then are not all the stars we see in the sky double but only about half of them?

Before the constellation disperses, the binary stars move through their natal region and the group members learn how to interact with other stars by gravity. "In many cases the groups split up and the stars scatter in the same way that pairs of dancers might separate after colliding with another couple on a crowded dance floor." explains Michael Marks, PhD student and member of the International School of Astronomy and Astrophysics of the Max Planck Institute. The population of binary stars is reduced before the stars disperse into the wider galaxy.

The star hotbeds are not uniform in structure and star density. The more pairs formed in the same space (dense group) the more interaction will occur and the more binaries will split into individual stars. This means that each cluster will exhibit a different composition of single stars and pairs when it disperses, depending on the initial density of the stars.

By using a model to calculate the composition of stars and pairs in regions of different density, the team of astronomers knows which types of star-forming regions will contribute individual stars and which will contribute star pairs to the galaxy as a whole. "This is the first time we have been able to calculate the contents of an entire galaxy, something that has not been possible until now. Now we can calculate with this method the star content in many galaxies and find how many single stars and how many pairs of stars exist.

to the notice of the researchers