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Astrophysics
E5 Stellar Processes and Stellar Evolution
IB Physics HL
Dublin Jerome High School
Chuck Crawford
Stellar processes and stellar evolution
Nucleosynthesis
E.5.1 Describe the conditions that initiate fusion in a star
E.5.2 State the effect of star’s mass on the end product of nuclear fusion
E.5.3 Outline the changes that take place in nucleosynthesis when a star
leaves the main sequence and becomes a red giant
Nucleosynthesis - creation of nuclei of
different elements as a result of fission
reactions
Stellar processes and stellar evolution
Nucleosynthesis
E.5.1 Describe the conditions that initiate fusion in a star
Cloud of gas comes together
loss of gravitational potential energy results in
and increase in kinetic energy
increase KE results in increase temperature
once ignition takes place star can remain
stable for billions of years
two positively charged particles (H or He)
need to be close enough for interaction
normally they would repel each other, so extremely high temp is necessary
if large cloud of H is hot enough then it can happen spontaneously
power radiated by the star is balance by power released in these reactions
this causes the temperature to stay constant
size of star remains stable because outward pressure is balanced by inward gravitational pull
Stellar processes and stellar evolution
Nucleosynthesis
E.5.2 State the effect of star’s mass on the end product of nuclear fusion
Sufficient mass of star results in fusion of higher
and higher elements
will come to an end with nucleosynthesis of iron
runs out of energy
iron nucleus has the greatest binding energy per nucleon of all nuclei
fusion of iron to form a higher mass nucleus would need to take in energy rather than release energy
Stellar processes and stellar evolution
Nucleosynthesis
E.5.3 Outline the changes that take place in nucleosynthesis when a star
leaves the main sequence and becomes a red giant
hydrogen starts to runs out
fusion occurs less often
no longer in equilibrium so gravitational forces
take over
and star collapses increasing temperature
helium fusion is now possible increasing
massively the star size
red giant - where outer layers are cooler
Stellar processes and stellar evolution
Evolutionary paths of stars and stellar processes
E.5.4 Apply the mass-luminosity relation
E.5.5 Explain how the Chandrasekhar and Oppenheimer-Volkoff limits are
used to predict the fate of stars of different masses
E.5.6 Compare the fate of a red giants and red supergiant
E.5.7 Draw evolutionary paths of stars on an HR diagram
E.5.8 Outline the characteristics of pulsars
Stellar processes and stellar evolution
Evolutionary paths of stars and stellar processes
E.5.4 Apply the mass-luminosity relation
relationship between the luminosity and mass
of a main sequence star
L=M
3.5
both L & M are in solar units
based largely upon observation of binary stars
Observations of thousands of main sequence stars show that there is definite relationship between their mass and their luminosity. The more massive main
sequence stars are hotter and more luminous than the low-mass main sequence stars. Furthermore, the luminosity depends on the mass raised to a power that
is between three and four (Luminosity ~ Massp, where p is between 3 & 4). This means that even a slight difference in the mass among stars produces a large
difference in their luminosities.
http://www.astronomynotes.com/starsun/s8.htm
Stellar processes and stellar evolution
Evolutionary paths of stars and stellar processes
E.5.5 Explain how the Chandrasekhar and Oppenheimer-Volkoff limits are
used to predict the fate of stars of different masses
Chandrasekhar limit is a ‘critical mass’ of the
initial star which dictates its evolution.
value is 1.4 times that of the sun
Stellar processes and stellar evolution
Evolutionary paths of stars and stellar processes
E.5.5 Explain how the Chandrasekhar and Oppenheimer-Volkoff limits are
used to predict the fate of stars of different masses
Oppenheimer-Volkoff limit - neutron star
value is 2-3 solar masses
Oppenheimer-Volkov limit
Neutron degeneracy pressure also has a mass limit, above which it cannot support the star. This limit occurs at 3 solar masses.
The neutron star collapses to a theoretical object called a quark star. Quark stars are not discovered, and have mostly unknown
properties. We do not yet know if they exist.
Stellar processes and stellar evolution
Evolutionary paths of stars and stellar processes
E.5.6 Compare the fate of a red giants and red supergiant
<4.0 Solar mass remnant becomes < 1.4
red giant planetary nebulae white dwarf
> 4.0 solar mass remnant becomes > 1.4
red supergiant supernova neutron star black hole
Stellar processes and stellar evolution
Evolutionary paths of stars and stellar processes
E.5.7 Draw evolutionary paths of stars on an HR diagram
Image Source: http://www.physics.hku.hk/~nature/CD/regular_e/lectures/chap15.html
Stellar processes and stellar evolution
Evolutionary paths of stars and stellar processes
E.5.7 Draw evolutionary paths of stars on an HR diagram
Image Source: http://www.physics.hku.hk/~nature/CD/regular_e/lectures/chap15.html
Stellar processes and stellar evolution
Evolutionary paths of stars and stellar processes
E.5.7 Draw evolutionary paths of stars on an HR diagram
Image Source: http://www.physics.hku.hk/~nature/CD/regular_e/lectures/chap16.html
Stellar processes and stellar evolution
Evolutionary paths of stars and stellar processes
E.5.7 Draw evolutionary paths of stars on an HR diagram
Image Source: http://www.physics.hku.hk/~nature/CD/regular_e/lectures/chap16.html
Stellar processes and stellar evolution
Evolutionary paths of stars and stellar processes
E.5.8 Outline the characteristics of pulsars
cosmic sources of very weak radio wave energy
pulsates rapidly at precise frequencies
believed to be rotating neutron stars
a rotating neutron star would be expected to emit an intense beam of radio waves in a specific direction
since it is rotating, the signal that is received is comes at regular pulses