Download Death of Stars

6. Stars evolve and eventually ‘die’
Describe the processes
involved in stellar
formation
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
Outline the key stages in
a
star’s life in terms of the
physical processes
involved
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
4. Fusion of
heavier elements
5. Helium
Depletion
5. Supernova
explosion
6. Planetary
Nebula and
White Dwarfs
6. Neutron
stars, pulsars
(too
massive)
6. Black Holes
Describe the types of nuclear
reactions involved in main
sequence and post-main
sequence stars
(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
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
Explain how the age of a cluster
can be determined from its zeroage main sequence plot for a H-R
diagram
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
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
Discuss the synthesis Can you discuss fusion
reactions up to iron
of elements in stars
then supernova synthesis?
Explain how the age of a
cluster
can be determined from its
zero-age main sequence plot
for a H-R diagram
Lower turn-off point from the main sequence indicates
High turn-off point shows there are
that there are not many high mass stars left so this
high mass stars present, so this cluster is
cluster is older - likely to be a globular cluster
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
Analyse information from
a H-R diagram and use
available
evidence to determine the
characteristics of a star and its
evolutionary stage
•Absolute magnitude
•Luminosity
•Spectral Type
•Colour
•Temperature
•Size
•Mass
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
Hayashi tracks
(end of last chapter)
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