Researchers from the Institute of Cosmos Sciences of the University of Barcelona (ICCUB) and the Institute of Space Studies of Catalonia (IEEC), in collaboration with the Institute of Astrophysics of the Canary Islands (IAC), have led the most extensive observational study to date of runaway massive stars, which includes an analysis of the rotation and binarity of these stars in our galaxy. This study, published today in the journal Astronomy & Astrophysics, sheds new light on how these stellar "runaways" are ejected into space and what their properties reveal about their fascinating origins.
Runaway stars are stars that move through space at unusually high speeds, drifting away from the places where they were born. For a long time, the way massive runaway stars acquire these high velocities has remained a mystery to astronomers, who have considered two main scenarios: a violent kick when a companion explodes as a supernova in a binary system, or a gravitational ejection during close encounters in dense, young star clusters. However, the relative contribution of these scenarios to explaining massive runaway stars in the Milky Way was not well understood.
Using data from the Gaia mission of the European Space Agency ( ESA ) and high-quality spectroscopic information from the IACOB project, the team analyzed 214 O-type stars, the most massive and luminous stellar objects in the galaxy. To understand their origins, they combined measurements of rotation speed and binarity (whether the star is single or part of a binary system) for the largest sample of galactic O-type runaway stars to date.
At what speed do runaway stars move and rotate?
The results reveal that most runaway stars rotate slowly, but those that rotate faster are more likely to be linked to supernova explosions in binary systems. Stars with the highest space velocities tend to be single, suggesting that they were ejected from young clusters through gravitational interactions.
