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Chapter Overview: The Bizarre Stellar Graveyard

White Dwarfs

• Definition: Remaining cores of dead stars, supported by electron degeneracy pressure against gravity.

• Cooling: They cool off and become dimmer over time.

• Size Comparison: White dwarfs are similar in size to Earth when they have the same mass as the Sun; higher-mass white dwarfs are smaller.

• White Dwarf Limit: Maximum mass (~1.4 times the Sun's mass) where electrons can't move faster than light, known as the Chandrasekhar limit.

Close Binary Systems

• Accretion Disks: Mass from the companion star falls toward the white dwarf, forming an accretion disk due to angular momentum, which heats up and glows from internal friction.

Novae

• What is a Nova? When the temperature of accreted matter becomes high enough for hydrogen fusion, resulting in a sudden explosion.

• Outcome: Nova temporarily brightens the star system and ejects accreted matter into space.

Supernovae

• Types of Supernovae:

  • Massive Star Supernova: Iron core collapses into a neutron star, causing a total explosion.

  • White Dwarf Supernova: Sudden carbon fusion in a white dwarf leads to explosion after reaching the 1.4MSun limit.

• Comparative Brightness: Supernovae are about 100,000 times more luminous than novae.

Neutron Stars

• Definition: Result from a massive-star supernova; supported by neutron degeneracy pressure.

• Size: Similar to a small city.

• Discovery: Pulsars detected as spinning neutron stars emitting regular radio emissions.

Black Holes

• Definition: Objects with gravity so intense that not even light can escape.

• Event Horizon: The radius where escape velocity equals the speed of light, known as the Schwarzschild radius.

• Neutron Star Limit: Neutron stars cannot exceed about 3MSun before collapsing into black holes.

• Singularity: Beyond the neutron star limit, all matter collapses into a single point.

Gamma-Ray Bursts

• Origin: Detected bursts of gamma rays tied to distant galaxies and likely linked to supernova explosions or neutron star collisions.

Mergers of Neutron Stars and Black Holes

• Neutron Star Mergers: Emit gravitational waves and can produce heavy elements in explosions.

• Black Hole Mergers: Observed with gravitational waves indicating massive black holes merging.