White Dwarfs, Neutron Stars, and Black Holes

Friction and Accretion

Friction in the accretion disk allows matter to accrete onto the white dwarf.

Cosmic Clocks

Pulsars used to measure time, though imperfect.

Angular Momentum Conservation

Principle explaining neutron star spin changes.

Crab Nebula

Location of a notable pulsar remnant.

Bizarre Physics

Unexplained phenomena near black holes requiring new theories.

Tidal Forces

Gravitational forces causing stretching near massive objects.

Stellar Black Hole

Black hole formed from a collapsing massive star.

Cooling of White Dwarfs

White dwarfs cool off and grow dimmer with time.

Higher-Mass White Dwarfs

Higher-mass white dwarfs are smaller.

Friction in Accretion Disks

Friction between orbiting rings of matter in the disk causes the disk to heat up and glow.

T Coronae Borealis (T CrB)

T CrB is expected to have an outburst where a new star will be visible for a period of time, reaching magnitude 2.

Thought Question 1

What would the gas in an accretion disk do if there were no friction? A. It would orbit indefinitely.

Thought Question 2

What happens to a white dwarf when it accretes enough matter to reach the 1.4M limit? A. It explodes.

Types of Supernova

Massive star supernova occurs when an iron core collapses into a neutron star or black hole; white dwarf supernova occurs when carbon fusion begins.

Light Curves of Supernovae

One way to tell supernova types apart is with a light curve showing how luminosity changes with time.

Supernova Type Classification

Massive star supernovae are labeled Type II; white dwarf supernovae are labeled Type Ia.

Neutron Star

A neutron star is a type of stellar remnant that is incredibly dense, formed from the remnants of a massive star after a supernova.

Discovery of Neutron Stars

Neutron stars were discovered through the observation of pulsars, which are rotating neutron stars emitting beams of radiation.

Close Binary System

In a close binary system, matter from one star can fall onto another, leading to phenomena like novae or supernovae.

Supernova Explosion

A supernova explosion occurs when a white dwarf reaches the mass limit and undergoes carbon fusion, resulting in a total explosion.

Spin Rate of Pulsars

Fast pulsars spin at ~1000 cycles per second.

Millisecond Pulsars

Neutron stars pulsating every few milliseconds.

X-ray Binaries

Close binaries with neutron stars emitting X-rays.

Neutrinos

Particles produced when electrons combine with protons.

Neutron Star Collapse

Occurs when neutrons collapse to form a neutron star.

Neutron Star Mass

Incredibly dense, leading to extreme gravitational effects.

Singularity

Point where gravity crushes matter into infinite density.

Three-Dimensional Representation

Visualizing four-dimensional spacetime in three dimensions.

Gravitational Waves

Ripples in spacetime caused by massive accelerating objects.

Massive Star Supernova

Explosive death of a star significantly larger than the Sun.

Neutron Star Merger

Collision of two neutron stars producing gravitational waves.

White Dwarf

A white dwarf is the remaining core of a dead star.

Electron Degeneracy Pressure

Electron degeneracy pressure supports white dwarfs against the crush of gravity.

Size of a White Dwarf

White dwarfs with the same mass as the Sun are about the same size as Earth.

White Dwarf Mass Limit

A white dwarf cannot be more massive than 1.4 times the mass of the Sun, known as the Chandrasekhar limit.

Accretion Disks

Mass falling toward a white dwarf from its close binary companion orbits the white dwarf in an accretion disk.

Nova

A nova occurs when the temperature of accreted matter becomes hot enough for hydrogen fusion, causing a sudden and explosive event.

Brightness of Nova

The nova star system temporarily appears much brighter than usual.

Nova vs Supernova

Supernovae are about 100,000 times brighter than novae; a nova involves H to He fusion while a supernova is a complete explosion of the white dwarf.

Chandrasekhar Limit

The Chandrasekhar limit is the maximum mass of a stable white dwarf, approximately 1.4 times the mass of the Sun.

Hydrogen Fusion

Hydrogen fusion occurs in a nova when the temperature of the accreted matter becomes sufficiently high.

Angular Momentum in Accretion Disks

Mass falling toward a white dwarf from its companion has angular momentum, causing it to orbit in an accretion disk.

Nova Brightness

During a nova, the star system can become significantly brighter than the Sun.

Magnitude Scale

Magnitude 6 is the limit our eyes can see under the best conditions; T CrB will be nearly 40 times brighter during its peak nova phase.

Degeneracy Pressure

Force preventing collapse under gravity in neutron stars.

Neutron Degeneracy Pressure

Pressure from neutrons supporting neutron stars.

Mass of Neutron Star

Approximately 300,000 times Earth's mass.

Accretion Disk

Disk formed by matter falling toward a neutron star.

Pulsar

Neutron star emitting radiation along a magnetic axis.

Pulsar Beams

Radiation beams sweeping through space like lighthouse beams.

Surface Rotation Velocity

Neutron stars can rotate at ~60,000 km/s.

Escape Velocity

Speed needed to escape a neutron star's gravity.

X-ray Bursts

Sudden fusion events producing X-ray emissions.

Neutron Star Discovery

First observed via regular radio pulses in 1967.

Gravity's Ultimate Victory

Concept describing the nature of black holes.

Black Hole

Object with gravity so strong that light cannot escape.

Neutron Star Size

Comparable to the size of a small city.

Jocelyn Bell

Astronomer who discovered pulsars using radio telescopes.

Pulsar Timing

Used to detect gravitational waves and test relativity.

Neutron Star Radiation

Radiation emitted due to rapid rotation and magnetic fields.

Neutron Star Formation

Results from the collapse of a massive star's core.

Iron Core Collapse

Process leading to neutron star formation during supernova.

Event Horizon

Boundary where escape velocity equals speed of light.

Schwarzschild Radius

Radius of a black hole's event horizon.

Neutron Star Limit

Mass threshold for neutron star stability, ~3 solar masses.

Gravitational Redshift

Light waves stretch due to strong gravitational fields.

Curvature of Spacetime

Bending of space due to mass presence.

Quantum Mechanics

Branch of physics governing subatomic particles.

General Theory of Relativity

Einstein's theory explaining gravity as spacetime curvature.

Kinetic Energy

Energy of an object due to its motion.

Potential Energy

Stored energy based on an object's position.

Mass

Amount of matter in an object, affecting gravity.

Speed of Light

Maximum speed of light in vacuum, ~299,792 km/s.

Gravitational Constant (G)

Constant used in calculating gravitational forces.

Black Hole Formation

Occurs when a massive star collapses under gravity.

Angular Momentum

Conserved quantity related to an object's rotation.

Mass Increase

Adding mass to a black hole enlarges its event horizon.

Light Escape

Light cannot escape if object radius is too small.

Bottomless Pit Analogy

Black holes compared to pits in spacetime.

Flat Spacetime

Two-dimensional representation of undistorted spacetime.

Supernova

Explosive death of a massive star, potentially forming black holes.

Mass Collapse

Process leading to black hole formation from stellar core.

Contact Loss

No information exchange once inside a black hole.

Orbiting Black Holes

Orbiting behaves like other massive objects if distant.

Spaghettification

Stretching effect due to tidal forces near a black hole.

Supermassive Black Hole

Black hole with millions to billions of solar masses.

X-ray Binary

Binary star system emitting X-rays, often containing black holes.

Gamma-Ray Burst

Brief, intense bursts of gamma rays from space.

Hypernova

Extremely energetic supernova possibly forming a black hole.

Kilonova

Explosion from merging neutron stars, producing heavy elements.

Orbital Properties

Characteristics of an object's orbit used to measure mass.

Binary System

System of two stars orbiting each other.

LIGO

Observatory detecting gravitational waves from cosmic events.

Black Hole Verification

Methods to confirm existence of a black hole.

Companion Star

Star orbiting another star in a binary system.

Cygnus

Constellation containing a notable black hole binary.

Gamma-Ray Detection

Observing gamma rays to identify cosmic events.

Event Detection

Identifying significant astronomical occurrences like mergers.

Time Dilation

Slowing of time experienced near massive objects.

Extreme Events

Significant astronomical phenomena like mergers and bursts.