1. 6. Stars evolve and eventually ‘die’
ASTROPHYSICS
Caroline Chisholm College
Physics
Describe the processes involved in stellar formation
THE FORMATION
OF STARS
Space is filled with gas, dust and molecules - a sparse interstellar medium
Stars form in dense clouds of this medium
Gravity of denser parts of the cloud starts to attract surrounding material
Increased rotation of core may lead to fragmentation that forms clusters and, later, planets
Restricted movement across magnetic fields causes a disc to form
Compression at the core causes temperature to rise, fusion occurs and a balance begins between thermal and gravitational pressure
A STAR IS BORN

2. ASTROPHYSICS 6. Black Holes 4. Helium flash 5. Helium Depletion
Outline the key stages in a star’s life in terms of the physical processes involved
Caroline Chisholm College
Physics
See the separate powerpoint presentation
(modified from an original NASA presentation)
on the 'Life Cycles of Stars' for more info
Remember high mass stars burn fuel more quickly, so spend a shorter time on main sequence
1. Formation
2. Main sequence
3. Red Giant expansion
<5Mo
>5Mo
4. Helium flash
5. Helium Depletion
6. Planetary Nebula and White Dwarfs
4. Fusion of heavier elements
5. Supernova explosion
(too massive)
6. Neutron stars, pulsars
6. Black Holes

3. Caroline Chisholm College
Physics

4. Caroline Chisholm College
ASTROPHYSICS
Caroline Chisholm College
Physics
Supernova remnant =
Dust/gas Cloud
(nebula)

5. Caroline Chisholm College
ASTROPHYSICS
Caroline Chisholm College
Physics
Dust/gas Cloud
(nebula)
Main sequence
star
Supernova

6. Caroline Chisholm College
ASTROPHYSICS
Describe the types of nuclear reactions involved in main sequence and post-main sequence stars
Caroline Chisholm College
Physics
(NOT correct particles here)
The PROTON-PROTON reaction and the CNO cycle both involve fusion of four Hydrogen nuclei to form a He nucleus and conversion of mass to energy
E = mc 2
The energy appears as K.E of the particles formed, high energy gamma rays and neutrinos
The temperature of the star’s core determines which process will dominate
The P-P process dominates in the Sun

7. ASTROPHYSICS CLUES TO STAR FORMATION AND AGES OF STARS
Explain how the age of a cluster can be determined from its zero-age main sequence plot for a H-R diagram
Caroline Chisholm College
Physics
Open clusters - few hundred stars, younger, high metal abundance, M to B stars, low and high mass main seq.stars, only few giant & supergiant stars
CLUES TO STAR FORMATION
AND AGES OF STARS
Globular clusters (pictured) - 100,000‘s of stars tightly bound, older, low metal abundance, mostly Hydrogen burning, M to G stars, low mass main sequence (MS) stars, many giant & supergiant high L stars
There is a ‘continuum’ of H-R cluster diagrams - moving from young (with high mass MS stars) (open) to old (no high mass MS stars) (globular).
MS turn-off point indicates age

8. ASTROPHYSICS turn-off point Caroline Chisholm College Physics
Can you discuss fusion
reactions up to iron
then supernova synthesis?
Caroline Chisholm College
Physics
Discuss the synthesis of elements in stars
Explain how the age of a cluster can be determined from its zero-age main sequence plot for a H-R diagram
turn-off point
Lower turn-off point from the main sequence indicates that there are not many high mass stars left so this cluster is older - likely to be a globular cluster
High turn-off point shows there are
high mass stars present, so this cluster is
younger and probably an open cluster
Present information by plotting Hertzsprung-Russell diagrams for: nearby or brightest stars; stars in a young open cluster; stars in a globular cluster
practical
exercises
5.2, 5.3

9. Caroline Chisholm College
ASTROPHYSICS
Analyse information from a H-R diagram and use available evidence to determine the characteristics of a star and its evolutionary stage
Caroline Chisholm College
Physics
Absolute magnitude
Luminosity
Spectral Type
Colour
Temperature
Size
Mass

10. Caroline Chisholm College
ASTROPHYSICS
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
Caroline Chisholm College
Physics
Hayashi tracks
(end of last chapter)

11. WHY STUDY ASTROPHYSICS?
Caroline Chisholm College
Physics
Gather, analyse information and use available evidence to assess the impact of increased knowledge in astrophysics on society
WHY STUDY ASTROPHYSICS?
To gain an understanding of our universe and our role in it
Learn about how the universe operates --> modern science
Study of our solar system allows us to study data from other planets and assess the nature of our planet, its origins and our resources
Space technology gives us communication satellites, accurate weather forecasts, GPS, minerals exploration, long term monitoring of earth
Observations lead to Laws such as Newtonian mechanics, which had applications for machines, construction and Industrial Revolution
Technology (e.g. medicine, materials, techniques) developed for space have valuable uses on earth
aaawww! it's over!