Login
langue du site
Anglais
Fermer le panneau
Votamatic
accueil
sondages ouverts
Stars & Planets - An introduction - Questionnary up to low-mass stars red giant branch.
Which Nuclear reaction dominates in the Sun
pp1
pp2
cno
triple-alpha
Which timescale is the shortest
Main sequence timescale
Kelvin Helmholtz timescale
Dynamical timescale
in a star that contracts quasi-statically (i.e. slowly enough to remain in hydrostatic equilibrium), the internal pressure
increases
decreases
The total energy of a bound star in hydrostatic equilibrium equals
1/3 of its gravitational potential energy
1/2 of its gravitational potential energy
All of the 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
Advective process
The main source of opacity in a massive star is
electron conduction
bound-free transitions
electron scattering
The first equation stellar structure describes
Energy transport
Heat 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 stellar age
The age and the mass of a star
The second equation of stellar structure provides a relation between
The local temperature and the local density.
the pressure and the gravitational forces
the nuclear reactions and the local pressure
Inside a star in hydrostatic equilibrium,
The pressure increases outwards
The pressure increases inwards
The pressure is constant
The equation of state of a gas relates
Pressure - time - density
Pressure - composition - density
Pressure - Temperature - density
The free-fall time is the time for a star to collapse if
The nuclear reactions stops in the core
The pressure forces disappeared
The gravitational force disappeared
What is the order of magnitude of the free-fall time of a 1 solar mass star
10 sec
2000 sec
2000 yrs
200 000 yrs
20 Myrs
During most of their life, stars evolve quasi-statically.
non
oui
The 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 composition (metallicity)
A star that constracts quasi-statically gets brighter.
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 away in the stellar wind
transfered to its planetary system
radiated away
During the formation of a star, the collapse is halted by the formation of the 1st core. It happens because
the dissociation of the hydrogen molecules compensates the gravitational energy
it has reached the hydrostatic equilibrium
the dust radiates in infrared and compensates for the gravitational energy
Which of these statements are true ? Along the main sequence...
The density increases in the core
The amount of hydrogen increases in the core
The temperature increases in the core
The total luminosity increases
Which of these are true ?
All low-mass stars (< 8Msun) have a degenerate core on the red-giant branch.
The perfect gas law is still valid to describe a 5 solar mass star up to the end of the red giant branch phase.
In a degenerate core, the pressure and temperature are decorrelated.
During the red giant branch of low-mass stars,
the convective envelope shrinks because the star cools down.
helium is burning on a shell above an inert core.
the product of the several nuclear reactions on the main sequence are brought to the surface by the convective motions (dredge-up)..
At the peak of their respective red giant branch,
A 5 solar mass star shines approximately 30 times brighter than a 1 solar mass star.
A 1 solar mass star shines approximately 3 times brighter than a 5 solar mass star.
A 1 and a 5 solar mass stars have the same luminosity.
Université de Genève
