5.10.6 Neutron Stars & Black Holes

• In the final evolutionary stages of a massive star's life cycle, the remnant left after a supernova explosion will either be:
  • A neutron star
  • A black hole

Characteristics of a Neutron Star

• Neutron stars are objects formed in stars with cores which have masses greater than the Chandrasekhar limit
• Neutron stars are:
  • Extremely dense
  • Very small

• To put into perspective how dense and small a neutron star is:
  • The density of a neutron star is 4 × 10¹⁷ kg m⁻³
  • The density of the Earth is 5 × 10³ kg m⁻³
  • The density of a white dwarf is 1 × 10⁹ kg m⁻³
  • A neutron star with the mass of the Sun would be only 30 km in diameter

• Some neutron stars rotate rapidly (up to 600 times per second) emitting bursts of highly directional electromagnetic radiation
  • These stars are called pulsars

Characteristics of Black Holes

• The core collapses into an infinitely dense point called a singularity
• A singularity is defined as:

A theoretical point at which matter is compressed to an infinitely small point and the laws of physics, as they are currently understood, break down

• The gravitational field is so strong that nothing, not even light, can escape it
  • This region is known as a black hole

• The boundary at which light and matter cannot escape the gravitation pull of the black hole is called the event horizon
• The escape velocity beyond the event horizon is greater than the speed of light, hence photons cannot escape from a black hole

Characteristics of a Black Hole