In active galaxies, their central engines may be temporarily fed by
A) a sudden surge of star formation.
B) a series of supernovae around the core.
C) the sudden collapse of the core into a supermassive black hole.
D) a close encounter with a neighbor galaxy.
E) the fusion of helium into carbon in their cores.
D
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Of the thousands of different isotopes known to exist,
a. most of them are radioactive b. only a couple can be used to build an atom bomb c. some are used in medical diagnosis and treatment d. most occur naturally e. all of the above
A binary star system in the constellation Orion has an angular separation between the two stars of 1.2 × 10^?5 radians. If ? = 5 × 10^?7 m, what is the smallest-aperture (diameter) telescope that may be used to resolve the two stars?
a. 10 cm b. 5 cm c. 50 cm d. 1 m e. 4 cm
In a pure resistive circuit, the phase angle between current and voltage is
A) 0. B) ?/2 radians. C) -?/2 radians. D) ? radians. E) 3?/4 radians.
Doubling the capacitance of a capacitor that is holding a constant charge causes the energy stored in that capacitor to
A) quadruple. B) decrease to one-half. C) double. D) decrease to one-fourth.