Question

1. The fusion of iron nuclei does not occur in stable stars. Why not? a) no star ever gets hot enough for iron fusion b) elements more massive than iron aren't stable c) iron fusion uses up energy rather instead of producing energy d) iron is destroyed in stars as soon as it is produced 2. The oldest stars in the galaxy have a ____ abundance of heavier chemical elements than the sun a) higher b) lower c) similar 3. The size of the Swarzchild radius depends on what property of black hole? a) age b) angular momentum c) chemical composition d) mass e) temperature 4. What is indicated by the absence of O and B stars in elliptical galaxies a) elliptical galaxies are young and have not had enough time to form any O and B stars b) Interstellar dust clouds hide the O and B stars from our sight c) ellipticals are the oldest galaxies and have already gone through the spiral stage d) The O and B stars originally in elliptical galaxies have all died and no new ones have been formed

Answer 1

1. The fusion of iron nuclei does not occur in stable stars because iron has the highest binding energy per nucleon, Hence it is the most stable element, all the element higher or lighter than iron are less stable. Heavier elements than iron when undergoes nuclear fusion, it uses up energy rather than releasing it, so it is hard to sustain a star by using up energy. So the best answer is (c), the answer could also include (b).

2. The oldest stars have fewer heavy elements as compared to young stars because the young stars are born from the remanants of supernova, which may already have heavy elements and these are also there at the starting stage of young stars. Hence younger stars have more heavier elements. So older stars in galaxy will have lower abundance of heavier chemical elements.

3. From the formula we know that, the radius is,

Hence it is dependent on the mass of the black hole (option (d)).