Research by PhD student Jonathan Dodd and Dutch astronomer Rene Odemeyer from the University of Leeds (UK) suggests that massive Be stars, previously thought to be part of double stars, could actually be “triple” star systems.MNRASNovember 21).
Be stars – also called “vampire stars” – are surrounded by a distinct disk of gas, similar to the disk of Saturn. But although the existence of these stars has been known for about 150 years, no one knew exactly how they formed.
Until now, astronomers have assumed that the disks are the result of the rapid rotation of Be stars, which could be caused by interaction with a nearby star. But from analyzing data from the European astronomical satellite Gaia, Dodd and Odemeijer now conclude that Be stars are part of systems consisting of three stars, rather than two.
Astronomers base their observations on Gaia’s observations of these stars. They analyzed the way stars move across the sky, both over periods of about ten years and over shorter periods of about six months. When a star moves in a straight line it is single, but if it shows a slight wobble, or better yet a spiral, there must be more than one star in play.
By applying this principle to both (ordinary) B stars As Be stars, astronomers have found that Be stars appear to have fewer companions on average than B stars, when the opposite is expected. The researchers then looked at another set of data to look for more distant companion stars, and found that in this case the number of companion stars for B and Be is roughly equal.
From this they conclude that in many cases a third star is involved, forcing the companion closer to the Be star – close enough to transfer mass from one star to another, forming the apparent disk. This would also explain why these companions did not appear: they simply became too small and too faint to be seen after the vampire star absorbed much of their mass. (any)