A space agency sends a probe to observe a white dwarf in a binary system. Fig. 1 shows matter moving from a larger companion star towards the white dwarf. E...
Question 1 Report
A space agency sends a probe to observe a white dwarf in a binary system. Fig. 1 shows matter moving from a larger companion star towards the white dwarf. Engineers monitor the rate at which gas collects because a sudden burst of radiation would affect the probe instruments. The white dwarf is the dense remnant of a star like the Sun.
(a) What was the stage immediately before the white dwarf formed? [1]
(b) Describe one property of a white dwarf that makes its gravitational field strong. [1]
(c) Which two particles combine in the main sequence fusion reaction of the original star? [1]
(d) Give one reason why the white dwarf itself does not normally produce energy by hydrogen fusion. [2]
This star is being studied by an observatory that records its surface temperature and brightness. Fig. 1 is a Hertzsprung-Russell diagram used in the report. Point P is a cool but very bright star. The astronomers compare it with a normal main sequence star before deciding where it is in its life cycle. Temperature decreases from left to right on this type of graph.
(a) Which named group of stars contains P? [1]
(b) What is meant by brightness in this diagram? [1]
(c) Describe two differences between P and a main sequence star at the same temperature. [2]
(d) Give the next major stage after P for a Sun-like star. [1]
Answer Details
White dwarf in a binary system
- (a) The stage immediately before a white dwarf is a red giant. [1]
- (b) A white dwarf has a very large mass in a very small volume, so it has very high density and a strong gravitational field. [1]
- (c) The particles that combine in the original star's main-sequence reaction are hydrogen nuclei, or protons. [1]
- (d) The white dwarf has used most of its hydrogen fuel, and its core is no longer undergoing sustained hydrogen fusion. [2]
Hertzsprung-Russell diagram
- (a) P is a red giant: it is cool but very bright. [1]
- (b) Brightness here means the energy emitted by the star each second, also called luminosity. [1]
- (c) At the same temperature, P is brighter and has a larger radius than a main-sequence star. [2]
- (d) The next major stage for a Sun-like star after the red giant is a white dwarf. [1]
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