Question 34Correct1.00 points out of1.00Question 35Correct1.00 points out of1.00What happens to the surface of a low-mass star after the helium core and shellfusion stages are completed?Select one:a. It stabilizes at the size of a red giant star, radiation pressure from belowbalancing gravity from the core, and will slowly cool for the rest of its life.b. It is spun off into space to make a spiral structure known as a spiral galaxy.c. It is propelled slowly away from the core to form a planetary nebula. Correct!d. It contracts back onto the core and becomes hot enough to undergo furtherhydrogen fusion, leading to a very hot and active white dwarf star.What is it that is actually located at the event horizon of a black hole?Where does gold (the element) come from?
Question 36Correct1.00 points out of1.00Question 37Correct1.00 points out of1.00Question 38Correct1.00 points out of1.00I always thought nothing could escape from a black hole, yet astronomers arelocating black hole candidates by the X rays they emit. How can X rays be comingfrom a black hole?Why does the core of the Sun contain more helium and less hydrogen than thesurface of the Sun?Select one:a. The hydrogen has been lifted out of the core by the Sun's magnetic field.b. Helium is heavier than hydrogen and has sunk toward the center in a processof chemical differentiation.c. Helium condenses more easily, so when the Sun was forming the corebecame helium-rich; vast quantities of hydrogen were added only after the corebecame massive enough.d. Thermonuclear reactions have converted much of the original hydrogen in thecore into helium. Correct!Giant and supergiant stars are rare because
Question 39Correct1.00 points out of1.00Question 40Correct1.00 points out of1.00Black holes are formed byApproximately what fraction of its main-sequence lifetime has the Sun completed atthe present time?