The key to identifying a black hole candidate in a binary system is that:
A) one of the two stars cannot be seen.
B) the unseen companion in the system must have a sufficiently high mass.
C) the unseen star is a contact binary.
D) the system must be a very strong source of radio emissions.
E) the visible companion must be an evolving main sequence or giant star.
B
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A fully charged parallel-plate capacitor remains connected to a battery while a dielectric is slid between the plates. Does DV increase, decrease, or stay the same?
1.increase 2.decrease 3.remains the same
We observe stars orbiting at distances of 25,000 light-years from the centers of Galaxy X and Galaxy Y. For this orbital distance, stars in Galaxy X have higher orbital speeds than stars in Galaxy Y. What can we conclude?
A) Galaxy X contains more total mass within 25,000 light-years of its center than Galaxy Y. B) Galaxy Y contains more total mass within 25,000 light-years of its center than Galaxy X. C) Galaxy X contains more dark matter than Galaxy Y. D) Galaxy Y contains more dark matter than Galaxy X. E) The stars of Galaxy X are more massive than those of Galaxy Y.
What is the Cassini division of Saturn's rings?
A) a dark ring, visible from Earth, composed of dark, dusty particles B) a large gap, visible from Earth C) the imaginary circle marking the halfway point of Saturn's rings D) the widest ring of Saturn, located between two large ring gaps E) the most opaque ring of Saturn, made of highly reflective ice particles
About what percent of Earth's surface is covered with water?
a. 70% b. 10% c. 50% d. 30%