Module Details

The information contained in this module specification was correct at the time of publication but may be subject to change, either during the session because of unforeseen circumstances, or following review of the module at the end of the session. Queries about the module should be directed to the member of staff with responsibility for the module.
Title The Interstellar Medium
Code PHYS495
Coordinator Dr S Longmore
Year CATS Level Semester CATS Value
Session 2021-22 Level 7 FHEQ Second Semester 15


To build upon the student's appreciation of the role which the interstellar medium (ISM) plays in topics as stellar evolution (star-forming regions to supernova remnants) and galaxy evolution.

To provide a firm physical framework for this appreciation by investigating in detail the mechanisms which govern the structure and appearance of the ISM.

Learning Outcomes

(LO1) An understanding of the structure and evolution of the ISM and the relationship between its various components

(LO2) The ability to list the various types of observable phenomena and relate them to the structure of the various phases of the ISM and the physical process at work

(LO3) Knowledge of how observation, specifically spectroscopy, allows astronomers to understand the physical conditions and chemical content of the ISM and thereby construct models of the interstellar medium and its relationship to the formation and evolution of stars and galaxies

(S1) Independent study skills



Review of Radiation Processes and Spectral Line emission

Spectral line formation. The interaction of a radiation field with matter. Radiative transfer

Physical Conditions in the ISM

The structure and phases of the Galactic interstellar medium. Photo ionisation and recombination in a pure hydrogen cloud (the HII region). The effects of including helium and heavier elements. Energy balance and thermal equilibrium. Free-free radiation. Collision ally excited emission lines, permitted and forbidden. Recombination lines. Continuum emission processes. Molecular emission, lines

Spectral Diagnostics

Determination of electron temperatures and densities from atomic spectral line and continuum measurements. Determination of elemental abundances. Tracers of dense molecular gas; mass measurements

Scattering and Polarisation

Introduction to theory and application of scattering of light by small particles. Polarisation by scattering and dichroic abso rption in reflection nebulae

Dust and Molecular Clouds

Formation and destruction of dust. Observable diagnostics. Formation of molecules on dust grains. Heating and cooling of molecular clouds. Molecular emission lines. Structure, dynamics, mechanical support and energy balance of molecular clouds. Magnetic fields, am-bipolar diffusion, gravitational contraction, star formation.

Introduction to Gas Dynamics

Sound waves and Alfven waves. Adiabatic and radioactive shock waves. Expansion of ionised regions. Stellar winds. Supernova remnants.

Teaching and Learning Strategies

The module is taught by directed reading and problem-solving. Students are expected to read a section of a textbook and attempt a set of problems every week, and the content and problems will be reviewed at weekly tutorial sessions.

Teaching Schedule

  Lectures Seminars Tutorials Lab Practicals Fieldwork Placement Other TOTAL
Study Hours     24

Timetable (if known)              
Private Study 126


EXAM Duration Timing
% of
Penalty for late
There is a resit opportunity. This is an anonymous assessment.  180 minutes    70       
CONTINUOUS Duration Timing
% of
Penalty for late
weekly problem sets. Standard UoL penalty applies for late submission. This is not an anonymous assessment.      30       

Recommended Texts

Reading lists are managed at Click here to access the reading lists for this module.