1.1. Algol is a triple-star system, with stars Aa1, Aa2 and Aa3 orbiting each other.

This triple-star is 90 light-years from the Earth.

Here is some data on the star Aa1. • radius = (1.90 ± 0.14) × 10⁹ m • mass = (6.31 ± 0.42) × 10³⁰ kg. Calculate the gravitational field strength g at the surface of Aa1 to 3 significant figures.

  Include the absolute uncertainty in your answer. Assume that the other stars of the system exert negligible gravitational force on Aa1.

g = .............................. ± .............................. N kg^–1 [4]

1.2. The table shows some data about the three stars of Algol.

Star Luminosity of star / L_Θ Surface temperature of star / K Aa1 182 13000 Aa2 6.92 4500 Aa3 10.0 7500

The luminosity of each star is in terms of the solar luminosity L_Θ.

i) Define the luminosity of a star.

[1]

ii) Use Stefan’s law to determine the ratio $\frac{radiusofstarAa2}{radiusofstarAa3}$

ratio = .......................................................... [2]

iii) Use Wien’s displacement law to explain which star would have the longest wavelength at the peak intensity of the emitted electromagnetic radiation.

[2]

iv) Suggest how an astronomer using just an optical telescope can deduce that the three stars of Algol have different surface temperatures.

[1]

v) The light from each star passing through a diffraction grating shows an absorption line spectrum.

Explain how a specific absorption line is produced in this type of spectrum in terms of photons and electrons.

[3]

1.3. The Aa1 star could evolve into a black hole. State two ways in which the black hole would differ from the Aa1 star. 1. ............................................................................................. 2. .............................................................................................

[2]