Theoretical Astro - Review

The relaxation time:

• can only be calculated for continuous distributions of mass

• is the time scale beyond which the effects of scattering become significant

• is proportional to the mass density and to the velocity dispersion cubed

Stellar systems have negative specific heat. This means that, in order to maintain equilibrium:

• if we supply energy, the total kinetic energy needs to decrease

• if we subtract energy, the total kinetic energy needs to decrease

• if we supply energy, the total kinetic energy needs to increase

• if we supply energy, the total potential energy needs to decrease

Which of the following modelling approaches is the one offering the most detailed description of the dynamics of a stellar system?

• virial equations

• kinetic theory

• N-body models

• fluid equations

An ergodic distribution function describes:

• anisotropic stellar systems

• rotating stellar systems

• isotropic stellar systems

• axisymmetric stellar systems

Which one of the following equations corresponds to the Poisson equation for a spherically symmetric system?

• 
• 
• 
• 

What is the most likely explanation for the flat rotation curves that we measure for spiral galaxies?

• mass-anisotropy degeneracy

• dark matter

• constant mass-to-light ratio

• solid body rotation

The mass-to-light ratio:

• is large for systems with very little dark matter

• does not change with position within a stellar system

• is not important to study the dynamics of a stellar system

• depends on the age and chemical properties of stars

The spherical Jeans equation:

• puts into relation the velocity dispersion and the gravitational potential

• is an example of fluid equation

• can be derived from the collisionless Boltzmann equation

• does not depend on velocity dispersion anisotropy

Orbits in isochrone potentials are closed

• True

• False

Which are, absolutely without any doubt, the best stellar systems in the Universe?

• elliptical galaxies

• spiral galaxies

• globular clusters

• nuclear star clusters