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The Question

(Submitted November 30, 1996)

What is known about Sagittarius A*,the center of our galaxy ?

The Answer

Sgr A* at the center of Milky Way is probably a massive black hole of about a million solar masses (the mass of the Sun). The mass is estimated from the motion of gas and stars in the region. Although Sgr A* is gathering mass from its vicinity at a rate of about 10E-4 solar masses per year, a rather high rate, it is not as bright as would be expected. Therefore, Sgr A* is extremely inefficient (one part in 100,000) in converting the gravitational energy of the gathered material into radiation.

Koji Mukai
with helps from Drs. Chen, Loewenstein and Snowden

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