9

9.7 Option — Astrophysics

Contextual Outline

The wonders of the universe are revealed through technological advances based
on tested principles of physics. Our understanding of the cosmos draws upon models, theories and laws in our endeavour to seek explanations for the myriad of observations made at many different wavelengths. Techniques, such as imaging, photometry, astrometry and spectroscopy, allow us to determine many of the properties and characteristics of celestial objects. Continual technical advancement has resulted in a range of devices extending from optical and radio-telescopes on Earth to orbiting telescopes, such as Hipparcos, Chandra and HST.

Explanations for events in our spectacular universe, based on our understandings
of the electromagnetic spectrum, allow for insights into the relationships between supernovae, star formation and evolution, and extreme events, such as high gravity environments of a neutron star or black hole.

Objects that generate high-energy radiations spanning the electromagnetic spectrum from radio to high-energy gamma rays are studied to further our understanding of nucleosynthesis, Type I and Type II supernovae and Einstein’s Law of relativity.

Outcomes

This module contributes to the following course outcomes:

A student:

H2 analyses the ways in which models, theories and laws in physics have been tested and validated

H4 assesses the impact of applications of physics on society and the environment

H7 explains the effect of energy transfers and transformation

H8 analyses wave interactions and explains the effects of those interactions

H9 explains the effects of electric, magnetic and gravitational fields

H11 justifies the appropriateness of a particular investigation plan

H12 evaluates ways in which accuracy and reliability could be improved in investigations

H13 uses terminology and reporting styles appropriately and successfully to communicate information and understanding

H14 assesses the validity of conclusions drawn from gathered data and information

H15 explains why an investigation is best undertaken individually or by a team

H16 justifies positive values about and attitudes towards both the living and non-living components of the environment, ethical behaviour and a desire for critical evaluation of the consequences of the applications of science.

1. Our understanding of celestial objects depends upon observations made from Earth or space near the Earth

Students learn to:

• recall the components of the electromagnetic spectrum and describe the properties of each component

• explain why some wavebands can only be detected from space

• define the terms resolution and sensitivity

• discuss the problems associated with ground-based astronomy in terms of resolution and selective absorption of radiation

• outline methods by which the resolution and sensitivity of ground-based systems can be improved, including:

– adaptive optics

– interferometry

Students:

• process information to discuss Galileo’s utilisation of the telescope to identify properties of the moon

• identify data sources, plan, choose equipment or resources for, and perform an investigation to demonstrate why it is desirable for telescopes to have a large diameter objective lens or mirror in terms of both sensitivity and resolution

• gather, process and present information on new generation optical telescopes

2. Careful measurement of a celestial object’s position, in the sky, (astrometry) may be used to determine its distance

• define the terms parallax, parsec, light year

• explain how trigonometric parallax can be used to determine the distance to relatively close stars

• discuss the limitations with trigonometric parallax measurements

• outline the results from astrometric satellites such as Hipparcos

• analyse information to calculate the distance to a star given its trigonometric parallax

• gather and process information to determine the relative limits to trigonometric parallax distance determinations using ground-based and space-based methods of measurement

· solve problems and analyse information using d = 1/p

3. Spectroscopy is a vital tool for astronomers and provides a wealth of information

Students learn to:

• account for the production
of emission and absorption spectra and compare these with a continuous blackbody spectrum

• describe the technology needed to measure astronomical spectra

• identify the general types of spectra produced by stars, emission nebulae, galaxies and quasars

• describe the key features
of stellar spectra and explain how this is used to classify stars

• describe how spectra can provide information on surface temperature, rotational and translational velocity, density and chemical composition of stars

• identify how Wien’s Law can assist in providing information about stellar composition

• explain qualitatively how Stefan’s Law is related to stellar radii

Students:

• process information to examine a variety of spectra produced by discharge tubes, reflected sunlight, incandescent filaments

• solve problem and analyse information to calculate the surface temperature of a star from its intensity/wavelength graph

• gather information about stellar spectra from either a first-hand investigation or second-hand sources and use available evidence to classify stars

4. Photometric measurements can be used for determining distance and comparing objects

• define absolute and apparent magnitude

• explain how the concept of magnitude can be used to determine the distance to a celestial object

• outline spectroscopic parallax

• explain how two-colour values (ie colour index, B-V) are obtained and why they are useful

• describe the advantages of photoelectric detectors over photographic methods for photometry

• solve problems and analyse information using:

and

to calculate the absolute or apparent magnitude of stars using photographic or digital data and a reference star

• perform an investigation to demonstrate why it is important to use filters for photometry

• identify data sources,
gather, process and present information to assess the impact of improvements in measurement technologies on understanding of the celestial objects

5. The study of binary and variable stars reveals vital information about stars

Students learn to:

• describe binary stars in terms of means of detection: visual, eclipsing, spectroscopic and astrometric

• explain the importance of binary stars in determining stellar masses

• classify variable stars as either intrinsic or extrinsic and periodic or non-periodic

• explain the importance of the period-luminosity relationship for distance determination

Students:

• perform an investigation
to model the light curves
of eclipsing binaries using computer simulation

• solve problems and analyse information by applying Kepler’s Third Law:

to calculate the mass of a star system

6. Stars evolve and eventually ‘die’

• describe the processes involved in stellar formation

• outline the key stages in a star’s life in terms of the physical processes involved

• describe the types of nuclear reactions involved in main-sequence and post-main sequence stars

• discuss the synthesis
of elements in stars

• explain how the age of a cluster can be determined from its zero-age main sequence plot

• explain the concept of star death in relation to:

– planetary nebula

– supernovae

– white dwarfs

– neutron stars/pulsars

– black holes

• present information by plotting Hertzsprung-Russell diagrams for: nearby or brightest stars; stars in a young open cluster; stars
in a globular cluster

• analyse information from
a H-R diagram and use available evidence to determine the characteristics of a star and its evolutionary stage

• present information by plotting on a H-R diagram
the pathways of stars from 0.1 to 10 solar mass during their life and relate the mass of the initial protostar to the final end point

• gather, analyse information and use available evidence to assess the impact of increased knowledge in astrophysics on society