High Frequency QPOs in Neutron Stars and Black Holes: Probing Dense Matter and Strong Gravitational Fields

Understand

Quasi-periodic oscillations (QPOs) have been discovered in the X-ray emission of many neutron stars and black holes.

• The QPOs with frequencies greater than about 300 Hz are thought to be produced near the surfaces of neutron stars and the event horizons of black holes.
• I first summarize some of the most important properties of the QPOs seen in neutron star and black hole systems.
• I then review some of the models that have been proposed and compare them with observational data.