How Have Astronomers Measured the Mass of the Black Hole

question 52

Multiple Choice

How have astronomers measured the mass of the black hole at the center of our galaxy?

• A) using the rotation curve derived from 21-cm emission
• B) by observing the motions of stars near the center of the galaxy
• C) by measuring the brightness of the quasar
• D) by measuring the Doppler shift of Sagittarius A*
• E) by counting the number of supernova explosions near the black hole during the last century

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Definitions:

Draft

A written order drawn on one person by another, requesting him to pay money to a designated third person.

Demand

A claim; a legal obligation; a request to perform an alleged obligation; a written statement of a claim. In corporation law, a request that the board of directors sue a person who has harmed the corporation; a prerequisite to a shareholder derivative suit.

Commercial Paper

Negotiable paper such as promissory notes, drafts, and checks that provides for the payment of money and can readily be transferred to other parties.

Unconditional Order

A directive that must be followed without any stipulations or requirements.