ASP Astrophysics Fundamentals 2

Question 1

What is the Schwarzschild radius?

Accepted Answer

The critical radius at which an object becomes a black hole (its escape velocity equals the speed of light)

Answer

The Schwarzschild radius is the radius to which a mass must be compressed to form a black hole, where the escape velocity equals the speed of light (rs = 2GM/c²); for the Sun it is about 3 km.

Question 2

What is nuclear binding energy?

Accepted Answer

The energy required to completely separate the nucleons (protons and neutrons) in an atomic nucleus

Answer

Nuclear binding energy is the energy required to disassemble an atomic nucleus into its constituent protons and neutrons; fusion of lighter elements releases energy when the products have higher binding energy per nucleon.

Question 3

What is the mass-luminosity relationship for main-sequence stars?

Accepted Answer

L ∝ M³·⁵ to M⁴ (approximately)

Answer

For main-sequence stars, luminosity scales approximately as L ∝ M³·⁵ to M⁴, meaning a star twice as massive as the Sun is roughly 10–16 times more luminous and consequently lives much shorter.

Question 4

What is escape velocity?

Accepted Answer

The minimum velocity needed for an object to escape a body's gravitational pull without further propulsion

Answer

Escape velocity is the minimum speed an object needs to escape a gravitational field without additional thrust, equal to v = √(2GM/r); for Earth it is about 11.2 km/s.

Question 5

What is the hydrostatic equilibrium condition in stars?

Accepted Answer

The balance between the inward gravitational force and the outward pressure gradient that keeps a star stable in size

Answer

Hydrostatic equilibrium is the condition where the outward pressure gradient force (thermal + radiation pressure) exactly balances the inward gravitational force at every point within a star, maintaining a stable structure.

ASP - Astronomical Society of the Pacific Exam Practice Test

ASP - Astronomical Society of the Pacific Exam Practice Test

ASP Astrophysics Fundamentals 2