Fig. 1 is a sketch from a telescope log. It shows a star at two times during a supernova. At the second observation, the gas shell has a diameter of 0.84 li...
Question 1 Report
Fig. 1 is a sketch from a telescope log. It shows a star at two times during a supernova. At the second observation, the gas shell has a diameter of 0.84 light-years. Twenty-one years earlier, its diameter was 0.42 light-years. Assume that the expansion rate has stayed constant. The astronomers use the result to plan when to observe the shell again.
(a) Calculate the increase in diameter each year, in light-years per year. [2]
(b) What event produced the expanding shell? [1]
(c) Describe why the shell contains elements heavier than hydrogen. [2]
(d) Give one measurement that could improve confidence in the calculated rate. [1]
Answer Details
(a) Find the change in diameter, then divide by the time interval:
\[0.84-0.42=0.42\text{ light-years}\]
\[\frac{0.42\text{ light-years}}{21\text{ years}}=0.020\text{ light-years per year}\] [2]
(b) The expanding shell was produced by a supernova. [1]
(c) Fusion in the original massive star made elements heavier than hydrogen. The supernova explosion then expelled these elements into the expanding shell. [2]
(d) Measure the shell diameter at more times, or repeat diameter measurements. This gives more evidence for whether the assumed constant rate is reliable. [1]
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