Astronomers Conduct Landmark Study of 214 Runaway O-Type Stars Using Gaia Mission Data

Scientists have recently concluded the most comprehensive study to date regarding massive stars that have been violently ejected from the galactic plane of the Milky Way. These celestial bodies, known as runaway stars, were analyzed through a detailed examination of 214 O-type stars to better understand the mechanisms responsible for their anomalous velocities. The findings of this extensive research have been formally published in the journal "Astronomy & Astrophysics." The project was coordinated by the Institute of Cosmos Sciences (ICCUB) at the University of Barcelona, Spain.

The investigation relied heavily on high-precision kinematic data captured by the European Space Agency’s (ESA) Gaia mission. By examining a sample of 214 O-type stars—the largest dataset of its kind currently available—researchers were able to evaluate critical parameters such as rotation speeds and binary status. A major highlight of the study was the discovery of twelve runaway binary systems, six of which are considered potential hosts for compact objects, including small black holes. This international effort saw contributions from the Institute of Cosmos Sciences (ICCUB), the Institute of Space Studies of Catalonia (IEEC), and the Institute of Astrophysics of the Canary Islands (IAC), with researcher Mar Carretero-Castrillo leading the study.

Data analysis allowed the scientific team to draw significant conclusions about the dominant forces behind these stellar expulsions. It was determined that the majority of runaway stars are characterized by slow rotation and a lack of companions, which strongly points toward gravitational ejection from dense stellar clusters. This theory is bolstered by the fact that globular clusters—tightly packed groups of stars found in the Milky Way's outer halo—can gravitationally propel individual stars to incredibly high speeds through complex interactions.

In contrast, runaway stars exhibiting faster rotation speeds appear to have received their momentum from a supernova explosion within a binary system. This evidence supports a long-standing hypothesis introduced by Dutch astronomer Adriaan Blaauw in 1961, which suggested that the explosive death of a companion star could effectively "launch" the remaining star into the cosmos. The identification of potential black hole candidates within these runaway binary systems provides astronomers with specific targets for future observational research and deeper exploration.

This work is of fundamental importance for our comprehension of stellar dynamics and the broader evolution of the Galaxy. Runaway stars play a crucial role in transporting heavy elements and energy far from their birthplaces, thereby shaping the interstellar medium. The ESA’s Gaia mission, which launched on December 19, 2013, has been instrumental in this field by providing unprecedented accuracy in measuring stellar parallaxes and velocities. This latest research expands upon previous studies that identified 106 O-type and 69 Be-type runaway stars, further confirming that O-type stars typically achieve significantly higher velocities.