Researchers discover why unusual ‘blue hook’ stars are hotter than Sun

Washington: Researchers have revealed why the blue hook stars, found in the center of many star clusters, are just half the mass of Earth’s sun, yet ten times hotter and much more luminous.

The international team found the so-called blue hook stars throws off their cool outer layers late in life because they are rotating so rapidly, making them more luminous than usual.

Team member Dr Antonino Milone, from ANU Research School of Astronomy and Astrophysics, said that 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 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 showed that the formation of stars in clusters do not all form at once and so these blue stars must form in a second generation of star formation, said co-author Dr Aaron Dotter, also from ANU Research School of Astronomy and Astrophysics.

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.

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