Why can't lower-main-sequence stars become giant stars?
What will be an ideal response?
Stars between 0.08 and about 0.4 solar mass, the red dwarfs, are mixed by convection, and so can't develop inert helium cores surrounded by unprocessed hydrogen. For this reason a red dwarf can never ignite a hydrogen shell and can't become a giant star.
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When a karate chop breaks a board with a 3000-N blow, the amount of force that acts on the hand is
A) zero. B) 1500 N. C) 3000 N. D) 6000 N.
The speed of FM waves will be observed to be c = 2.9979 × 10^8 m/s when the antenna emitting the waves is
a. at rest relative to the receiving antenna. b. moving to the right of the detecting antenna at 0.5 c. c. moving to the left of the detecting antenna at 0.5 c. d. moving as described in (a), (b) or (c) above. e. moving at 2.9979 × 10^8 m/s.
Gas falling into a black hole:
a. is heated to millions of degrees through the loss of gravitational energy b. is cooled to near absolute zero through the loss of gravitational energy c. releases energy, all of which is absorbed by the black hole d. never reaches the black hole due to the effect of time dilation e. orbits the black hole but cannot cross the event horizon
This photo shows Comet Hale-Bopp in the night sky. Suppose you had taken another photograph from the same spot 10 minutes after this photo was taken. How would the scene have appeared at that time?
A) It would have looked virtually the same. B) We'd still see the same stars, but the comet would be out of sight, having passed below the horizon. C) We would see lots of smoke coming from the point where the comet crashed into the mountains. D) We'd still see the same stars, but the comet would have moved far enough so that we'd be able to see only its tails and not its coma above the horizon.