Scientists at the Institute of Space Sciences of the University of Barcelona have discovered a group of stars that are about to leave the Milky Way galaxy. The discovery is reported in the article, published in the journal Astronomy and Astrophysics.
The researchers analyzed data from two star catalogs – the O-type Star Catalog (GOSC) and the Be-type Star Spectra (BeSS). It also used astrometric measurements of the positions, distances and velocities of one billion stars based on data obtained by the Gaia spacecraft.
417 O-type stars and 1335 Be-type stars were found, present both in the Gaia database and in catalogs. Scientists have identified 106 runaway O-type stars, representing 25.4 percent of the stars in the GOSC catalog, with forty-two of them newly identified. Among Be-type stars, 69 runaway stars have been identified, representing 5.2 percent of the stars in the BeSS catalogue. In general, O-type stars move faster than Be-type stars.
OB stars often form in binary pairs. In a double supernova scenario, the explosion throws off the other star, which breaks the gravitational bond with its partner and even escapes the gravitational pull of the entire galaxy. In this case, it will head into intergalactic space. In a dynamic ejection scenario, the star experiences gravitational interactions with other stars. This is common among O and Be stars because they are found in close groups called OB associations.
The higher fraction of runaway stars and higher velocities found among O-type stars compared to Be-type stars indicate that a dynamic ejection scenario is more likely than a binary supernova scenario. Previous studies also show that dynamic ejection often results in faster and more frequent escapes than the binary supernova scenario.
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