Test 3

X-ray Binary

A system where a neutron star or black hole pulls material from a companion, emitting X-rays.

Neutron Star

A very dense remnant of a supernova, about 10 km in radius and 1.3-3 times the mass of the Sun.

Pulsar

A rapidly spinning neutron star that emits beams of radiation from its magnetic poles.

Lighthouse Model

Explains pulsar pulses as beams sweeping past Earth, like a lighthouse.

Pulsar Wind

High-speed atomic particles emitted by pulsars, carrying most of their energy.

Millisecond Pulsar

A neutron star that rotates hundreds of times per second.

Black Widow Pulsar

A pulsar that strips material from its low-mass companion star.

Proper Motion

The apparent motion of a star across the sky due to its actual motion through space.

Accretion Disk

Hot, glowing disk of material spiraling into a compact object.

Gamma-Ray Burst (GRB)

An extremely energetic explosion detected as a burst of gamma rays.

Magnetar

A neutron star with an extremely strong magnetic field.

General Relativity

Einstein's theory that gravity is due to the curvature of spacetime by mass and energy.

Equivalence Principle

States that gravity and acceleration are indistinguishable in a small region.

Gravitational Time Dilation

Time moves slower near a massive object.

Gravitational Lensing

Light bends around massive objects, like black holes or galaxy clusters.

Globular Cluster

A spherical collection of old stars that orbits the galactic core.

Galactic Disk

Flat region of a galaxy with stars, gas, and dust, including the spiral arms.

Galactic Halo

Spherical region around a galaxy, containing old stars and globular clusters.

Galactic Bulge

Dense central region of a spiral galaxy, mostly older stars.

Spiral Density Wave Theory

Suggests spiral arms are waves of star formation caused by compression.

Self-Sustaining Star Formation

Ongoing star formation triggered by supernovae and ionization fronts.

Standard Candle

An astronomical object with known luminosity, used to measure distance.

Cepheid Variable

A type of star that varies in brightness in a regular way, used as a standard candle.

Type Ia Supernova

An exploding white dwarf with consistent brightness, used to measure distance.

Distance Modulus

A formula that relates an object's brightness to its distance.

Kepler's Third Law

Describes the relationship between orbital period and distance from the mass center.

Rotation Curve

A graph of orbital speed vs. distance from center; flat curves suggest dark matter.

Virial Theorem

Relates the average kinetic and potential energy to estimate mass of clusters.

Dark Matter

Unseen mass that affects galaxy rotation and gravitational lensing.

MACHO

Massive Compact Halo Object, a type of dark matter candidate.

WIMP

Weakly Interacting Massive Particle, a hypothetical form of dark matter.

Hubble's Law

States that galaxies move away faster as they are farther from us.

Look-back Time

The time light from a distant object has traveled to reach us.

Three Types of Compact Objects

White dwarfs, neutron stars, and black holes — end stages of stellar evolution based on mass.

Neutron Star Mass Limits and Support

Form from cores between ~1.4 and 3 solar masses; supported by neutron degeneracy pressure.

Discovery of Pulsars

Discovered in 1967 as regular radio pulses; linked to rotating neutron stars.

Pulsar Energy Loss

Emit radiation and particles, losing energy and slowing rotation over time.

X-ray Burster

Binary system where accreted matter causes periodic X-ray outbursts on a neutron star.

Black Hole Definition

Region with gravity so strong not even light can escape; observed by effects on nearby matter.

Singularity, Event Horizon, Schwarzschild Radius

Singularity: core of a black hole; event horizon: boundary; Schwarzschild radius: critical radius for light escape.

Calculate Schwarzschild Radius

Rs = 2GM/c²; use mass to calculate event horizon radius.

Gravitational Redshift

Light loses energy escaping strong gravity, shifting to longer wavelengths.

Searching for Black Holes

Look for X-rays, star motion, and gravitational lensing as indirect evidence.

Gamma-ray Bursts & Hypernovae

Short GRBs from neutron star mergers; long GRBs from massive star explosions.

Evidence for MW Disk Shape

Star counts, dust lane, and shape of star distribution indicate disk shape.

Herschel's Error on Sun's Location

Didn't account for dust dimming; thought Sun was near center.

Shapley's Galaxy Center Method

Used variable stars in globular clusters to estimate galaxy center.

Problems in Shapley's Calibration

Incorrect variable types and no dust correction caused distance errors.

Shapley's Key Contribution

Showed Sun is not at the center of the Milky Way.

MW Galaxy Components

Disk, bulge, halo — each with distinct star populations and structures.

Measuring Galaxy Mass

Use Kepler's law for orbits or galaxy rotation curves.

Rotation Curve & Galaxy Mass

Flat rotation curves show more mass than visible — dark matter.

Tracing Spiral Arms

Use star associations, Cepheids, HII regions, and 21-cm hydrogen maps.

Spiral Arm Formation Models

Spiral density wave theory and self-propagating star formation.

O and B Stars in Spiral Arms

Short-lived stars die near their birthplaces — spiral arms.

Observing Galactic Center

Dust blocks optical view; use infrared and radio wavelengths.

Population I and II Stars

Pop I: younger, metal-rich, in disk; Pop II: old, metal-poor, in halo.

Galactic Center Black Hole Evidence

Rapid star orbits around an invisible, massive object.

Element Enrichment of ISM

Supernovae and stellar winds release heavier elements.

Galaxy Formation Models

Monolithic collapse and hierarchical merging models.

Galaxy Classifications

Spiral, elliptical, and irregular — differ in shape and star content.

Distance Indicators

Cepheids, Type Ia supernovae, brightest stars — each with limits.

Look-back Time

Light from far objects shows them as they were long ago.

Redshift to Distance

Use redshift to find velocity, then apply Hubble's Law.

Galaxy Mass Importance

Mass affects structure, dynamics, and evolution.

Rotation Curve Method

Flat curve implies mass beyond visible edges — dark matter.

Supermassive Black Holes in Galaxies

Detected by star motion and high-energy emissions.

Interacting Galaxies

Galaxies that affect each other gravitationally.

Galactic Cannibalism

Larger galaxy absorbs a smaller one.

Starburst Galaxy

Rapid star formation due to interactions or mergers.

MW-Andromeda Collision Result

Likely to form a large elliptical galaxy.

Galaxy Cluster

A group of galaxies held together by gravity, ranging from a few to thousands of galaxies.

Rich Cluster

Contains 1,000 or more galaxies, about 3 Mpc in diameter, condensed around a central galaxy.

Poor Cluster

Has fewer than 1,000 galaxies, loosely bound and not condensed toward a center.

Tidal Tail

Elongated streams of stars and gas created by gravitational interactions during galaxy collisions.

Ring Galaxy

Formed by a high-speed, face-on collision with another galaxy, showing a ring-like appearance.

Active Galactic Nucleus (AGN)

A small region at a galaxy's center emitting large amounts of energy.

Radio Galaxy

A galaxy that emits strong radio waves, often with jets and radio lobes.

Seyfert Galaxy

A spiral galaxy with a very bright nucleus and rapid gas motion.

Quasar

An extremely luminous AGN with a high redshift, often very distant.

Radio Lobe

Regions of intense radio emission located outside the visible galaxy, powered by jets.

Jet

Streams of high-speed gas ejected from the center of active galaxies.

Synchrotron Radiation

Radiation produced by charged particles spiraling in magnetic fields, common in jets.

Supermassive Black Hole

A black hole with millions to billions of solar masses at the center of galaxies.

Accretion Disk

A rotating disk of gas and dust falling into a black hole, heated to extreme temperatures.

Unified Model of AGN

A theory suggesting all types of AGNs are fundamentally the same, viewed differently.

X-ray Flare

A sudden burst of X-rays, sometimes as powerful as a supernova, observed in AGNs.

Tidal Interaction

Gravitational effects during close encounters or mergers of galaxies.

Redshift

A measure of how much the wavelength of light is stretched by the expansion of the universe.