Module 10 Neutron Stars

Life Cycle of Stars
  • Main Sequence Phase
    • Most of a star's life is spent here.
    • Nuclear reaction: Hydrogen fusion produces helium.
  • Transition from Main Sequence
    • When hydrogen is depleted, the star changes location on the HR Diagram.
    • Location Factors: Size of the star.
    • Helium fusion begins to form carbon once hydrogen is used up.
    • Low mass stars (up to 8 times the Sun's size) experience a “helium flash” as helium fuses.
Evolution of Low Mass Stars
  • Helium Fusion
    • Generates carbon, leading to the expansion of the star into a red giant.
  • Instability Phase
    • Carbon runs out causing instability and pulsations.
  • Planetary Nebula Formation
    • Outer layers are expelled, creating a cloud of gas and dust (misnamed as "planetary nebula" as it involves no planets).
  • End Stage
    • Only the core remains, becoming a White Dwarf Star.
    • No further nuclear fusion occurs; it only emits heat radiation.
    • Eventually cools down and becomes a Black Dwarf, roughly the size of a planet.
Evolution of High Mass Stars
  • Carbon Fusion
    • When helium is exhausted, the weight of the outer layers forces the carbon core to collapse, raising temperatures to fuse carbon into heavier elements (oxygen, neon, magnesium).
  • Further Nuclear Fusion
    • As additional nuclear fuels exhaust, the core collapses again to reach temperatures high enough for further fusion (silicon, sulfur, calcium, argon).
    • The process continues until iron is formed.
Iron Core Collapse in High-Mass Stars
  • Collapse Effect
    • The iron core collapses.
  • Resulting Explosion
    • Post-collapse, the star expands back to original size and undergoes a supernova explosion.
  • Outcomes
    • Smaller high-mass stars transform into neutron stars.
    • Larger high-mass stars may become black holes.
Neutron Stars
  • Formation
    • Created when a massive star runs out of fuel and collapses.
  • Characteristics
    • Rapidly rotating neutron stars are known as pulsars.
    • Emit pulses of radiation at regular intervals, akin to a lighthouse.
    • Possess extremely strong magnetic fields which direct jets of particles along two magnetic poles.
Discovery of Neutron Stars (Pulsars)
  • Jocelyn Bell's Contribution
    • In the 1960s, as a graduate student at Cambridge University, she utilized a radio telescope to study the twinkling of distant stars.
    • Discovered repeating radio waves occurring every second, initially labeling them as LGM for "Little Green Men."
    • Soon recognized these signals were from pulsars, which are neutron stars.