Read the observation below. A university telescope detects a star that gives out intense X-rays. A visible companion star orbits it, and gas from the compan...
Question 1 Report
Read the observation below. A university telescope detects a star that gives out intense X-rays. A visible companion star orbits it, and gas from the companion appears to be pulled into a small region. The source itself cannot be seen directly. The astronomers suggest that it may be a black hole formed after the death of a massive star.
(a) What force pulls gas towards the possible black hole? [1]
(b) Describe why the black hole cannot normally be seen by light from its surface. [2]
(c) Give one reason why X-rays may still be detected from material near it. [1]
A researcher reads a case study of an exploding star observed in another galaxy. Before the explosion, images showed a red supergiant. After the explosion, telescopes found a rapidly expanding cloud but could not immediately identify the remnant. The researcher uses Fig. 1 to decide between two possible outcomes for the core.
(a) What determines whether the final object is a neutron star or a black hole? [1]
(b) Which outcome is more likely if the remaining core has the greatest mass? [1]
(c) Give one observation that would show gas from the supernova is still moving outwards. [1]
(d) Describe one importance of supernovae for later stars and planets. [1]
Answer Details
First investigation
- (a) Gas is pulled towards the object by gravity, also called gravitational force. [1]
- (b) A black hole has an extremely strong gravitational field. Light cannot escape from it, so no light from a visible surface can reach an observer. [2]
- (c) Gas falling towards the black hole becomes very hot and emits X-rays. The X-rays come from nearby material, not from the black hole itself. [1]
Second investigation
- (a) The outcome depends on the mass of the remaining core (or the mass of the original star). [1]
- (b) The greatest remaining core mass is more likely to form a black hole. [1]
- (c) An expanding shell has an increasing diameter. Alternatively, a spectral shift showing outward velocity would provide evidence. [1]
- (d) Supernovae spread heavy elements into space. These materials can later become part of new stars and planets. [1]
Examination reminder: distinguish radiation emitted by hot infalling gas from light escaping a black hole. The latter cannot escape.
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