Astronomy and Astrophysics – Astrophysics – Galaxy Astrophysics
Scientific paper
2009-06-30
Astronomy and Astrophysics
Astrophysics
Galaxy Astrophysics
5 pages, 3 figures, accepted by MNRAS LETTER
Scientific paper
We determine the spin of a supermassive black hole in the context of discseismology by comparing newly detected quasi-periodic oscillations (QPOs) of radio emission in the Galactic centre, Sagittarius A* (Sgr A*), as well as infrared and X-ray emissions with those of the Galactic black holes. We find that the spin parameters of black holes in Sgr A* and in Galactic X-ray sources have a unique value of $\approx 0.44$ which is smaller than the generally accepted value for supermassive black holes, suggesting evidence for the angular momentum extraction of black holes during the growth of supermassive black holes. Our results demonstrate that the spin parameter approaches the equilibrium value where spin-up via accretion is balanced by spin-down via the Blandford-Znajek mechanism regardless of its initial spin. We anticipate that measuring the spin of black holes by using QPOs will open a new window for exploring the evolution of black holes in the Universe.
Kato Yusuke
Matsumoto Ryo
Miyoshi Makoto
Negoro Hitoshi
Takahashi Ryoji
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