By Alexandra Ka Po Yip, MAS´ and IFA UV postdoctoral researcher
A very high fraction of stars are found in pairs or small groups, bound together by their mutual gravitational attraction. The components of these systems (usually referred to as “binaries” and “multiple systems”) interact gravitationally with each other and with other stars in the Milky Way. These interactions can lead to the gradual weakening of the bonds between the components, eventually causing the system to become unbound. Disintegrating systems are thought to be common, however, since the time for the disintegration to take place is ~1 million years (short in astronomical terms but very long for human endeavors) they can be extremely difficult to identify. Furthermore, such interactions as well as breaking up the system, might also release low-mass stars, brown dwarfs, or planets, which were previously bound to one of the stars.
Brown dwarfs are known as intermediate objects between stars and planets, and hold the key to bridge the gap between the two. They are very small and dim compared to normal stars, as can be see in the image, showing the bright star Eta Cancri and its brown dwarf companion Eta Cancri B (the small brown dot inside the white circle to the right of the bright star, which is zoomed-in at the bottom right corner – image from Zhang et al. 2010).
There has been some limited analysis of disintegrating multiple systems in the Milky Way to date, however no actual disintegrating candidate that consists of at least one brown dwarf has been identified so far. To search for possible disintegrating systems, the first step is to identify objects that are close in the sky and at the same distance from us. The next step is to separate gravitationally bound systems from unbound disintegrating systems. Objects in wide multiple systems move in the same direction at the same speed, while those in disintegrating systems do not.
In my paper (https://zenodo.org/record/59237#.Wa3PpTCGPeM) I have identified one disintegrating quadruple system and two double systems, each containing a brown dwarf. The candidate disintegrating systems identified in my work should be examined further using more accurate and precise data provided by the satellite Gaia and dedicated observations. Gaia will also provide a much larger catalogue of stars and brown dwarf to search for additional disintegrating systems.