| Date | May 2014 | Marks available | 3 | Reference code | 14M.3.HL.TZ2.4 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | State | Question number | 4 | Adapted from | N/A |
Question
This question is about stellar evolution.
Achernar may evolve to become a neutron star.
Achernar is a main sequence star with a mass that is eight times the mass of the Sun. Deduce that Achernar has a greater temperature than the Sun.
Outline why Achernar will spend less time on the main sequence than the Sun.
(i) State the condition relating to mass that must be satisfied for Achernar to become a neutron star.
(ii) Some neutron stars rotate about their axes and have strong magnetic fields. State how these stars may be detected.
Markscheme
from the mass–luminosity relation, Achernar has a higher luminosity; { (reference to mass–luminosity is essential)
so it is above/to the left of the Sun on the main sequence / temperature increases with luminosity in the main sequence;
Ignore irrelevant statements that \(L = \sigma A{T^4}\).
Allow second marking point even if only mass is discussed.
Achernar has greater luminosity/temperature and so fuses hydrogen at a (disproportionately) higher rate than the Sun / OWTTE;
so it will run out of hydrogen/move to red giant region in less time than the Sun / OWTTE;
(i) the remnant mass/the mass of its core/the mass after the supernova stage; { (do not allow “mass” bald)
must be between the Chandrasekhar and Oppenheimer limits / \(1.4{M_\square } < {M_{{\text{core}}}} < 3{M_\square }\); { (allow answer in words or numerical values)
Allow 2.5 \({M_\square }\) to 3 \({M_\square }\) as O–V limit.
(ii) detection of EM radiation from pulsars/stars that pulsate / stars whose intensity varies rapidly / OWTTE;
Accept answers that refer to any regions of the electromagnetic spectrum.
Examiners report
In (a) most candidates correctly referred to the mass-luminosity equation, but then asserted that luminosity was proportional to temperature without consideration of a star’s surface area.
(b) was answered well by most.
In (c)(i) the Chandrasekhar and Oppenheimer-Volkoff limits (or their values) were both expected but not often provided. Also it was common to refer to a star's 'mass' rather than 'remnant mass' or 'mass of the core'. Many candidates realised that a pulsar was being described in (c)(ii).
