Quasars and other active galactic nuclei are often intense sources of x-rays. According to the supermassive black hole hypothesis, where are these x-rays produced?
A) in hot gas in an accretion disk around the central black hole
B) in ionization nebulae heated by supernovae near the black hole
C) in dust-rich molecular clouds that are forming new stars near the black hole
D) in the central black hole itself
A) in hot gas in an accretion disk around the central black hole
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The planet COROT-14b is only slightly larger than Jupiter, but is several times more massive. Which is the most plausible explanation for its similar size to Jupiter?
A) Planets that are close to a star are heated up and therefore larger. B) The mass measurement is mistaken, and it is actually about 10 times more massive than Jupiter. C) It is made of elements other than hydrogen and helium which do not compress under their own gravity. D) The hydrogen and helium gas compressed even under their own gravity to a higher density than Jupiter.
The binding energy of the hydrogen atom in its ground state is -13.6 eV. What is the energy when it is in the n = 5 state?
A) 2.72 eV B) -2.72 eV C) 0.544 eV D) -0.544 eV E) -68 eV
What kind of variable stars are pre-Main Sequence stars undergoing gravitational contraction and exhibiting erratic changes in their luminosities?
A) R Coronae Borealis B) RR Lyrae C) Cepheid D) T Tauri E) Herbig-Haro
The tip of the needle of a sewing machine executes simple harmonic motion with an amplitude of 1.2 cm and an angular frequency ? = 62 rad/s. What is the total distance traveled by the needle in 1.9 s?
A) 27 cm B) 40 cm C) 1.1 cm D) 90 cm E) 140 cm