Study estimates that around 10 million stars are ‘fleeing’ the Milky Way

2023-11-19 09:41:00

Massive stars in the Milky Way are moving independently of the galaxy, indicating an escape towards intergalactic space, escaping the gravitational pull of the galaxy. This phenomenon was recently recognized by observing catalogs of stars in our universe, in a study carried out by researchers who analyzed the distribution of velocities, observing those that were not in sync with the galactic rotation.

Although the exact number of runaway stars is not known, a study led by Mar Carretero Castrillo and published in the journal Astronomy and Astrophysics estimates something in the range of 10 million. Astronomers used the Galactic O-Star Catalog (GOSC) and Be Star Spectra (BeSS), along with data from ESA’s Gaia telescope, to identify dozens of these runaway stars.

The two catalogs catalog massive, young and hot stars, with GOSC and BeSS responsible for recording different types. The joint analysis resulted in the identification of 417 O-type stars and 1,335 B-type stars present in Gaia and in the GOSC and BeSS catalogs, respectively. Notably, 106 O-type stars (25.4% of GOSC) and 69 B-type stars (5.2% of BeSS) were identified as escaping the Milky Way.

“The higher percentages and velocities found for O-type escapees compared to Be-type escapees highlight that the dynamic ejection scenario is more likely than the binary supernova scenario,” the study points out.

Two theories have been proposed to explain this phenomenon: the binary supernova scenario (BSS) and the dynamical ejection (DES). While in BSS a binary pair causes one star to explode, releasing enough energy to eject the other out of the galaxy, in DES, gravitational interactions in a compact and dense environment cause a star to flee, without the need for an explosion. Comparative analysis of the data suggests that the likely explanation for runaway stars favors dynamical ejection.

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