(ORDO NEWS) — Astronomers from the University of Georgia, USA, have found an explanation for the unusual arrangement of massive stars, which are found too far from the place of their formation, in the disk of our Milky Way galaxy.
Stars more massive than the Sun have very hot cores that generate huge amounts of nuclear energy. They are among the brightest objects in the galaxy. But since the hydrogen in massive stars burns out very quickly, the life cycle of such stars is usually short and can be about 10 million years, versus 10 billion years for stars like the Sun.
Such a short lifespan of massive stars means that they simply do not have time to travel far from where they formed. Most massive stars are found in the flat disk of the Galaxy, where gas clouds are dense enough to stimulate the birth of new stars and where astronomers find young clusters of massive stars.
So when a massive star is discovered “far from home”, astronomers always ask the question – how did it get there?
“Astronomers find massive stars far from where they formed, so far away that the lifespan of a star isn’t long enough to cover that distance,” said astronomer Douglas Gies of Georgia State University. “The question of how such a massive star could get to its current location is actively debated in the scientific community.”
It is this problem that occurs in the case of the massive star HD93521, which lies at a distance of about 3600 light years above the plane of the galactic disk of the Milky Way. In a new study, Gies and colleagues show that the star simply could not have had time to get so far from the disk plane, where active star formation occurs.
Using the Gaia satellite of the ESA, the authors showed that the life cycle of this star with a mass of about 17 solar masses is about 5 million years, while it takes about 39 million years to cover a distance of 3600 light years.
According to Gies and his colleagues, the key to the mystery of the star is that HD93521 was previously a binary system, a close pair of small Sun-like stars that eventually merged into a single giant star.
Since the duration of the life cycle of not very massive stars is much longer compared to massive stars, the duration of the movement of a binary system through the Galaxy could be tens of millions of years, the authors explained.
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