Neutron Stars and Black Holes

• What forms after a supernova ejects a star's outer layers?

  Neutron stars
• What is the mass range for a core to become a neutron star?

  1.4 to 3 solar masses
• How is a neutron star defined?

  As an extremely dense collapsed star made of neutrons
• What is the approximate density of a neutron star?

  ~$10^{17} \text{ kg m}^{-3}$
• What would be the diameter of a neutron star with the mass of the Sun?

  About 30 km
• How much would a teaspoon of neutron star weigh?

  About 100 million tonnes
• What process combines electrons and protons into neutrons in a neutron star?

  Reverse beta decay
• What prevents further collapse of a neutron star?

  Neutron degeneracy pressure
• What are rapidly rotating neutron stars called?

  Pulsars
• Why are pulsars easier to identify than non-rotating neutron stars?

  They emit radiation periodically
• What types of radiation do pulsars emit?

  Radio waves, X-rays, and gamma rays
• What can happen to the most massive cores after a supernova?

  They can collapse into a black hole
• What is a singularity in the context of black holes?

  An infinitely dense point
• What mass must a core exceed to become a black hole?

  Greater than 3 solar masses
• What is the event horizon of a black hole?

  The boundary where light cannot escape
• What is the escape velocity beyond the event horizon?

  Greater than the speed of light
• Why can't black holes be seen directly?

  Photons cannot escape beyond the event horizon
• What is the Schwarzschild radius?

  The radius of a black hole's event horizon
• What is the formula for the Schwarzschild radius?

  $R_s \approx \frac{2GM}{c^2}$
• What is the mass of Sagittarius A*?

  4 million solar masses
• What evidence suggests supermassive black holes exist in galaxies?

  Mass equivalent to millions of stars in small volume
• How many supermassive black holes have been identified?

  Over 150
• What is the event horizon's significance in black holes?

  It marks the point of no return for light
• What are the steps to calculate the Schwarzschild radius?

  1. Identify mass of the black hole.
  2. Use the formula: $R_s =$$\frac{2GM}{c^2}$.
  3. Substitute known values for G and c.
  4. Calculate the radius.
• Compare the density of solar-mass black holes to supermassive black holes.

  • Solar-mass black holes are denser.
  • Density inversely proportional to mass.
  • Supermassive black holes have lower density.
• What are the characteristics of pulsars?

  • Fast-rotating neutron stars.
  • Emit radiation periodically.
  • Easier to detect than non-rotating neutron stars.
• What happens to the core of a massive star after a supernova?

  • Can become a neutron star or black hole.
  • Depends on the core's mass.
  • Neutron stars form from 1.4 to 3 solar masses.
  • Black holes form from cores greater than 3 solar masses.
• What is the relationship between mass and density in black holes?

  • More massive black holes are less dense.
  • Density inversely proportional to mass.
  • Solar-mass black holes are denser than supermassive black holes.