Stellar Dynamics — MCQs

1. Stellar dynamics is primarily concerned with the study of?
(A) Nuclear fusion in stars
(B) Motion of stars under mutual gravity
(C) Planetary orbits
(D) Chemical composition of stars

2. The Virial Theorem relates?
(A) Kinetic and potential energy in a gravitational system
(B) Temperature and luminosity of stars
(C) Mass and radius of black holes
(D) Pressure and density of gas clouds

3. Two-body relaxation time describes?
(A) The cooling time of a star
(B) Time for stellar encounters to redistribute energy
(C) Time for nuclear burning in stars
(D) Age of the galaxy

4. Which type of star cluster is most useful for stellar dynamical studies?
(A) Open clusters
(B) Globular clusters
(C) Associations
(D) Dwarf galaxies

5. The Jeans instability criterion determines?
(A) Star collapse under gravity
(B) Stellar nuclear fusion rate
(C) Supernova explosion threshold
(D) Orbital motion of planets

6. The N-body problem in stellar dynamics refers to?
(A) Motion of one star
(B) Exact solution for multiple gravitating stars
(C) Stellar evolution models
(D) Neutron star mergers

7. Which method is commonly used to simulate stellar dynamics?
(A) Monte Carlo method
(B) Spectroscopy
(C) Photometry
(D) Interferometry

8. Equipartition of energy in star clusters causes?
(A) High-mass stars to move faster
(B) Low-mass stars to move faster
(C) All stars to have the same velocity
(D) Clusters to dissolve

9. The process by which massive stars sink toward the center of a cluster is called?
(A) Stellar fusion
(B) Mass segregation
(C) Supernova fallback
(D) Stellar drift

10. Escape velocity in a star cluster determines?
(A) Minimum speed for a star to leave the cluster
(B) Maximum speed of cluster rotation
(C) Speed of nuclear fusion products
(D) Rate of supernova explosions

11. A star cluster that is losing stars due to tidal forces is said to be?
(A) Dissolving
(B) Relaxed
(C) Stable
(D) Virialized

12. Which galaxy property can be explained using stellar dynamics?
(A) Galaxy colors
(B) Rotation curves
(C) Metallicity
(D) Star formation rate

13. The distribution function in stellar dynamics describes?
(A) Stellar masses
(B) Stellar orbits and velocities
(C) Star colors
(D) Star luminosities

14. The Maxwell-Boltzmann distribution is applied in stellar dynamics to describe?
(A) Nuclear energy levels
(B) Stellar velocity distribution
(C) Star formation rates
(D) Supernova frequencies

15. The Oort constants are related to?
(A) Galactic rotation
(B) Stellar fusion
(C) Star lifetimes
(D) Neutron star collapse

16. Dynamical friction causes massive objects to?
(A) Speed up
(B) Spiral inward
(C) Escape the galaxy
(D) Maintain constant velocity

17. Which cluster has shorter relaxation times?
(A) Globular clusters
(B) Open clusters
(C) Galaxy clusters
(D) Dwarf galaxies

18. Which law governs the gravitational interaction of stars?
(A) Newton’s law of gravitation
(B) Coulomb’s law
(C) Ampere’s law
(D) Kepler’s third law only

19. Chandrasekhar’s work in stellar dynamics is famous for?
(A) Mass limit of white dwarfs
(B) Dynamical friction theory
(C) Black hole thermodynamics
(D) Neutron star equation of state

20. The King model is used to describe?
(A) Stellar collapse
(B) Density distribution in star clusters
(C) Stellar evolution
(D) Stellar winds

21. Core collapse in globular clusters is caused by?
(A) Stellar winds
(B) Energy transfer between stars
(C) Nuclear fusion
(D) External tidal forces only

22. A tidal tail forms when?
(A) A star explodes
(B) A cluster interacts with a galaxy
(C) A star collapses
(D) A planet migrates

23. Stellar streams are remnants of?
(A) Disrupted star clusters
(B) Collapsing nebulae
(C) Binary star systems
(D) Supernova remnants

24. In phase space, Liouville’s theorem states?
(A) Phase space density is conserved
(B) Energy is lost in collisions
(C) Entropy always decreases
(D) Velocity distributions are random

25. The half-mass radius of a cluster is defined as?
(A) Radius enclosing all stars
(B) Radius enclosing half the cluster mass
(C) Average distance between stars
(D) Maximum tidal radius

26. Which quantity is constant for stars in a gravitationally bound system according to the Virial Theorem?
(A) Total momentum
(B) Total angular momentum
(C) Total energy
(D) Kinetic energy only

27. A cluster reaches “virial equilibrium” when?
(A) It stops forming stars
(B) 2K + U = 0, where K is kinetic energy and U is potential energy
(C) All stars have equal mass
(D) All stars move in circular orbits

28. Which process leads to the evaporation of star clusters?
(A) Nuclear fusion in stars
(B) Stellar encounters transferring energy
(C) Black hole mergers
(D) Dark matter annihilation

29. What is meant by “stellar relaxation”?
(A) Balancing nuclear reactions in a star
(B) Redistribution of stellar velocities due to encounters
(C) Slowing of stellar rotation
(D) Cooling of stellar cores

30. The Plummer model is used to describe?
(A) Stellar atmosphere layers
(B) Spherical star cluster density profiles
(C) Neutron star interiors
(D) Stellar fusion processes

31. Which galaxy component is most influenced by stellar dynamics?
(A) Dark matter halo
(B) Stellar disk and bulge
(C) Interstellar gas
(D) Magnetic fields

32. Which star type typically dominates the mass of star clusters?
(A) Massive O-type stars
(B) Intermediate and low-mass stars
(C) Neutron stars
(D) Black holes

33. Which timescale is shorter in open clusters compared to globular clusters?
(A) Nuclear timescale
(B) Relaxation timescale
(C) Stellar evolution timescale
(D) Cosmological timescale

34. Galactic bars are explained by?
(A) Supernova activity
(B) Non-axisymmetric stellar dynamics
(C) Black hole jets
(D) Dark energy effects

35. The dynamical time of a system refers to?
(A) Time for a star to orbit once in the system
(B) Time for nuclear fusion to occur
(C) Time for a supernova explosion
(D) Time for cosmic expansion

36. Which effect allows detection of central black holes in galaxies?
(A) X-ray emission only
(B) Stellar orbital velocities near the center
(C) Neutrino emission
(D) Pulsar timing

37. The concept of Jeans length is important in?
(A) Nuclear physics
(B) Star cluster stability
(C) Gravitational collapse of gas clouds
(D) Galactic rotation curves

38. In stellar systems, anisotropy refers to?
(A) Different stellar chemical compositions
(B) Unequal velocity distribution in different directions
(C) Unequal star masses
(D) Random stellar ages

39. Which process contributes to the core collapse of globular clusters?
(A) Mass segregation
(B) Nuclear fusion exhaustion
(C) Stellar winds
(D) Binary star disruption

40. Which approximation is often used in stellar dynamics?
(A) Mean-field approximation
(B) Quantum field approximation
(C) Magnetohydrodynamic approximation
(D) String theory approximation

41. Stellar streams observed in galaxies are evidence of?
(A) Star formation bursts
(B) Tidal disruption of smaller systems
(C) Supernova remnants
(D) Dark energy fluctuations

42. The study of galaxy mergers uses stellar dynamics to explain?
(A) Star colors
(B) Formation of elliptical galaxies
(C) Formation of neutron stars
(D) Chemical enrichment

43. The Schwarzschild orbit superposition method is used to?
(A) Solve the N-body problem exactly
(B) Construct galaxy dynamical models
(C) Simulate star fusion
(D) Model black hole evaporation

44. A dynamically “hot” system has?
(A) High velocity dispersion
(B) Low velocity dispersion
(C) Cold molecular gas
(D) Stable circular orbits only

45. Which is an example of a dynamically cold system?
(A) Globular cluster
(B) Galactic disk
(C) Elliptical galaxy
(D) Bulge of a spiral galaxy

46. Which mechanism can eject stars from clusters?
(A) Gravitational slingshot during encounters
(B) Nuclear burning in stars
(C) Supernova neutrinos
(D) Magnetic fields

47. The relaxation time of a galaxy compared to clusters is?
(A) Shorter
(B) Longer
(C) Equal
(D) Infinite

48. Which principle underlies Liouville’s theorem in stellar dynamics?
(A) Conservation of phase-space density
(B) Conservation of angular momentum only
(C) Conservation of energy only
(D) Conservation of entropy

49. Which property makes globular clusters excellent testbeds for stellar dynamics?
(A) Their chemical composition
(B) Their spherical symmetry and high stellar density
(C) Their strong magnetic fields
(D) Their binary star fraction

50. The primary challenge in solving the N-body problem for stellar dynamics is?
(A) The long lifetimes of stars
(B) The chaotic nature of gravitational interactions
(C) The lack of stellar observations
(D) The simplicity of Newton’s laws