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Stars and planets - An introduction - questionnary 20241127
Which nuclear reactions dominate in the Sun?
pp1
pp2
cno
triple-alpha
Which timescale is the shortest?
main sequence timescale
Kelvin-Helmoltz timescale
Dynamical timescale
In a star that contracts quasi-statically (i.e. slowly enough to remain in hydrostatique equilibrium), the internal pressure
increases
decreases
The total energy of a bound star in hydrosatique equilibrium equals
1/3 of its gravitational potential energy
1/2 of its gravitational potential energy
all its gravitational potential energy
When a star contracts, half of its gravitational potential energy is heating the star
non
oui
When a star contracts, half of its gravitational potential energy is radiated away
non
oui
The transport of energy by radiation is a
diffusive process
convective process
The main source of opacity in a massive star is
electron conduction
bound-free transitions
electron scattering
The first equation of stellar structure describes
energy transport
energy transport
mass conservation
hydrostatic equilibrium
The first equation of the internal structure of stars links
The radial mass distribution in the star to the local density
The local density to the age of the star
The age of a star to its mass
The second equation of the internal structure of stars provides a relation between
the age of a star and its mass
the pressure and the gravitational forces
the nuclear reactions and the local pressure
Inside a star that is in hydrostatic equilibrium
the presure decreases outwards
the presure increases outwards
the pressure is constant in the entire star
The equation of state of a gas relates
pressure, age, and mass
pressure, temperature, density
pressure, age, and mass
The free fall time is the time for a star to collapse if
the temperature of the star increases suddenly
the time a star spends on the main sequence
the time for a solar mass star to explode as a supernova
the time for a star to collapse if pressure forces disappear
What is the order of magnitude of the free fall time of a 1 solar mass star
10 sec
2000 sec
2'000 years
200'000 yrs
2 Gyrs
During most of their lifetime, stars evolve quasi-statiscally
non
oui
he virial theorem relates
the gravitational potential energy and the internal energy of a gaseous system
the surface temperature and the mass of a star
the expansion of a gaseous sphere and its metallicity
A star which contracts quasi-statically gets
non
oui
A star is bound if its total energy is
positive
negative
Half of the energy liberated by the contraction of a star is used for heating the star. The other half is
blown in the stellar wind
transfered to its planetary system
radiated away
Université de Genève