Topic questions Space physics Astronomical distances
6 questions · 41 marks · about 55 minutes
The apparent position of a star changes by an angle of 1.0 × 10– 4 degrees between observations made 6 months apart from the same place on Earth.
What is the distance of the star from Earth in parsecs?
A 2.8
B 5.6
C 170
D 330
Calculate the magnitude of the recession velocity of M87.
velocity =........ km s–1
Estimate the distance in light years to M87 using Hubble’s law.
Hubbles constant Ho = 2.5 × 10–19 s–1
Estimate the percentage uncertainty in the distance calculated in part (b) using the width of the emission line in the diagram.
percentage uncertainty = +/–........ %
Other methods have shown M87 is actually 50 million light years from Earth.
Suggest why M87 might contradict Hubble’s law.
Suggest one reason why the Big Bang theory is still the accepted model of the origin of the Universe.
The Hipparcos space telescope used stellar parallax with a precision of 9.7 × 10–4 arcseconds to determine the distance to stars.
One of the stars studied was Polaris A. Data about this star is in the table below.
| Parallax angle | 7.5 × 10–3 arcseconds |
| Radius | 2.1 × 1010 m |
| Mass | 1.1 × 1031 kg |
| Surface temperature | 6000 K |
| Temperature of the atmosphere of the star | 4.0 × 106 K |
Estimate the maximum stellar distance in parsecs that could be measured using Hipparcos.
Calculate the percentage uncertainty in the calculated value of the distance to Polaris A.
A continuous stream of particles called a solar wind flows from the surface of the star into the surrounding space.
These particles include helium nuclei of mass 6.6 × 10–27 kg.
Assume that the atmosphere is modelled as an ideal gas.
Show that the typical kinetic energy of a helium nucleus in the atmosphere is about 10–16 J.
The gravitational potential energy of a helium nucleus in the outer layer of the star is –2.3 × 10–16 J.
Calculate the gravitational potential energy U at the maximum distance from the star that a helium nucleus could reach.
Calculate the distance from the centre of the star reached by this helium nucleus.
Explain why the star has a solar wind that reaches a much greater distance from the star than found in (iii).
A pulsar is a rapidly rotating neutron star that emits radio waves.
Describe the formation of a neutron star.
State one characteristic of a neutron star.
An astronomer uses a radio telescope to observe a pulsar.
The graph below shows the power that the telescope receives due to the radio waves from one full rotation of a pulsar.
By calculating the area between the curve and the horizontal axis, estimate the total energy received by the telescope in one full rotation of the pulsar.
The surface area of the telescope is about 3000 m2. (ii)
The distance to the pulsar is about 300 pc.
By assuming that the radiation from the pulsar is emitted equally in all directions, estimate the total energy emitted in one full rotation.
Use your answer in (i) to calculate the distance d of Proxima Centauri from the Earth in light-years (ly).
1 pc = 3.26 ly
Estimate the gravitational force between two neighbouring galaxies.
Show that the mean density of the Universe is about 7 × 10–29 kg m–3. (ii)
Suggest why the actual mean density of the Universe is different from the value calculated in (ii).
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