Which of the following statements about Supernova 1987A is FALSE? a. it exploded relatively close to us, in a spiral arm of the Milky Way Galaxy b. it was only visible from the Southern Hemisphere c. astronomers believe it was the explosion of a star that was originally a massive type O e. it was observed with instruments in space as well as on the ground

You discover a binary star system in which one member is a 15 solar-mass main-sequence star and the other star is a 10 solar-mass giant. Why should you be surprised, at least at first? A. It doesn't make sense to find a giant in a binary star system. B. The two stars in a binary system should both be at the same point in stellar evolution; that is, they should either both be main-sequence stars or both be giants. C. The two stars should be the same age, so the more massive one should have become a giant first. D. The odds of ever finding two such massive stars in the same binary system are so small as to make it inconceivable that such a system could be discovered. E. A star with a mass of 15 solar-mass is too big to be a main-sequence star.

In a star of 1 solar mass (M☉), the core hydrogen burning phase, also known as the main sequence phase, lasts for approximately 10 billion years. Suppose there's a star of 15 solar masses (M☉). Stars of higher mass burn through their hydrogen at a faster rate, following an approximate relation that the lifetime of a star on the main sequence (T) is proportional to its mass (M) raised to the power of -2.5 (T ∝ M^-2.5). Calculate approximately how long this 15 solar mass star would remain in the main sequence phase, compared to the 1 solar mass star.

Which of the following is the least likely reason that astronomers consider supernova 1987A so important? Group of answer choices   The event confirmed theoretical predictions that much of the energy of a supernova explosion is emitted in the form of neutrinos.   Supernova 1987A was the first observable supernova in the Milky Way since the invention of the telescope.   Because supernova 1987A was relatively close and very little dust intervenes between us and the Large Magellanic Cloud, from which the supernova originated, astronomers were able to figure out its total energy output with pretty good accuracy.   The neutrinos preceded the light because they escaped during the collapse, whereas the first light of the explosion was emitted only after the supernova shock had plowed through the body of the star to the surface.   Supernova 1987A represented the first time astronomers had observed a star and knew its basic properties before it exploded.