This is an artist's impression of
the early life of a blue hook star and the destruction of its
proto-stellar disc by another star.
Credit: Marco Galliani, INAF
Astronomers have solved a mystery over
small, unusually hot blue stars, 10 times hotter than our Sun, that are
found in the middle of dense star clusters.
The international team found the so-called blue hook stars throw off
their cool outer layers late in life because they are rotating so
rapidly, making them more luminous than usual.
"We've solved an old puzzle. These stars are only half the mass of
our Sun yet we could not explain how they became so luminous," said team
member Dr Antonino Milone, from The Australian National University
(ANU) Research School of Astronomy and Astrophysics.
"As the star was forming billions of years ago from a disc of gas in
the congested centre of the star cluster, another star or stars must
have collided with the disc and destroyed it."
The research, published in Nature, gives new insights into
star formation in the early Universe in the crowded centres of clusters.
Star clusters are rare environments in the Universe, in which many
stars are born at the same time.
The team studied the globular cluster Omega Centauri, the only
cluster visible to the naked eye, which contains around 10 million stars
in close proximity to one another.
The model shows the formation of stars in clusters do not all form at
once, said co-author Dr Aaron Dotter, also from ANU Research School of
Astronomy and Astrophysics.
"These blue stars must form in a second generation of star
formation," he said. "Our new explanation is quite simple, and it hangs
together really nicely."
Usually the large disc of ionised gas around a newly-forming star
locks its rotation through magnetic effects. For the progenitors of blue
hook stars, however, an early destruction of its disc allows the stars
to spin up as the gas comes together to form a star.
Because its high rotation rate partially balances the inward force of
gravity, the star consumes its hydrogen fuel more slowly and evolves
differently throughout its life.
The blue hook phase of its life occurs after more than 10 billion
years, when the star has consumed nearly all its hydrogen and begins
burning the hotter fuel helium. The different evolution processes leave
it with a heavier core which burns brighter than typical helium-burning
stars.
Story Source:
The above post is reprinted from
materials provided by
Australian National University.
Note: Materials may be edited for content and length.
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