Cosmology (AQA A Level Physics)

Astronomers recently used the radial velocity method to discover an exoplanet orbiting HD 66141.

Describe the main features of the radial velocity method in the detection of planets.

Figure 2 shows, for some galaxies, how their recession speed varies with distance from the Earth.

Figure 2

Estimate, using Figure 2, the age in seconds of the Universe.

The estimate in part (a) assumes that the Universe has expanded at a constant rate.

Measurements involving type 1a supernovae that are at large distances from Earth caused astronomers to make a modification to this assumption.

State:

• the modification

• the explanation that was proposed to account for this modification.

U Cephei is an eclipsing binary system consisting of two stars that orbit their common centre of mass.

The primary star is class B; the secondary star is class G.

Figure 1 shows the variation of apparent magnitude of U Cephei with time as observed from Earth.

Figure 1

Explain the shape of the graph in Figure 1.

A particular spectral line has a wavelength of 486.136 nm when measured from a source in the laboratory.

This line is also present in the absorption spectrum of the primary star of U Cephei.

When observed from Earth, the wavelength of the primary star’s absorption line varies as shown in Table 1.

Table 1

State why the average of the values in Table 1 is different from the laboratory value.

Show that the orbital speed of the primary star is about 250 km s⁻¹.

Calculate the orbital radius of the primary star.

Which absorption lines would be most prominent in the spectrum of the primary star?

A different eclipsing binary star system is thought to consist of a white dwarf star and a neutron star.

Discuss how astronomers could confirm this.

IC2497 is a galaxy that contained a quasar. It is believed that the quasar stopped emitting radiation several thousand years ago.

Suggest why the quasar stopped emitting radiation.

IC2497 has a red shift of 0.0516

Determine the distance from the Earth to IC2497.

Give an appropriate unit for your answer.

Table 3 contains information about two galaxies.

Table 3

Discuss whether these data are consistent with Hubble’s Law.

Quasars are the most distant measurable objects.

Discuss one problem associated with the determination of the distance from the Earth to a quasar.