Neutron Stars and Black Holes

Neutron Stars

  • Formed after a Type II supernova, where a part of the core remnant survives.
  • Extremely dense, comparable to the density of an atomic nucleus.

Neutron Star Properties

  • Held in equilibrium by neutron degeneracy.
  • Mass: 1.4 - 3 solar masses.
  • Size: Very small compared to white dwarfs (which are ~1 solar mass and Earth-sized).
  • Density: Extremely high. ½ cm³ is equivalent to 100 million tons.
  • Weight: A person weighing 150 lbs on Earth would weigh 10 billion tons on a neutron star.
  • Rotation: Collapsing parent star causes rapid spinning, conserving angular momentum; typical periods are fractions of a second.
  • Magnetic field: Collapse intensifies the magnetic field, becoming trillions of times stronger than Earth's.
  • Gravity: High density results in high gravity.

Pulsars

  • Discovered in 1967 by Jocelyn Bell.
  • Emit small, regular pulses of radiation.
  • Rapidly spinning neutron stars.
  • Nobel Prize won in 1974.

Pulsar mechanism

  • Lighthouse effect: Strong jets of matter emitted at magnetic poles due to fast rotation.
  • If Earth aligns with the radiation path, pulses are observed as the star rotates.

Pulsar Characteristics

  • Radiate energy, weakening and eventually stopping after tens of millions of years.
  • Not all neutron stars are observed as pulsars because jets may not point towards Earth.
  • Pulsars are a subclass of neutron stars: All pulsars are neutron stars, but not all neutron stars are pulsars.
  • Crab Nebula contains a pulsar at its center, visible in both the “off” and “on” states.
  • Radiate in radio and gamma-ray spectra.
  • Examples: Crab pulsar (period = 0.33 s), Geminga pulsar (period = 0.24 s).

Magnetars

  • Subclass of neutron stars with extremely powerful magnetic fields (thousand trillion times stronger than Earth's).
  • Form if the original star spun fast enough with a strong magnetic field.
  • Undergo high-energy flare events due to