Lectures 21 & 22: Galaxy Evolution

Photons

Light particles traveling from distant galaxies.

10 billion years

Time light takes to reach Earth from distant galaxies.

Ancient light

Light from young galaxies observed in deep space.

Protogalactic clouds

Dense regions forming from gravitational collapse.

Conservation of angular momentum

Principle explaining the rotation of gas disks.

Spiral Galaxy

Galaxy type with rotating disk and spiral arms.

Elliptical Galaxy

Galaxy type with smooth, featureless light distribution.

Hubble's tuning fork diagram

Classification system for galaxy shapes and types.

Halo stars

Stars formed in collapsing gas toward galaxy centers.

Elliptical galaxy formation

Process of star formation in dense protogalactic clouds.

Distant red ellipticals

Galaxies formed early, observed as red due to age.

Tidal Tails

Stretched stars caused by gravitational interactions of galaxies.

Gravitational collapse

Process where matter pulls together to form structures.

Density fluctuations

Small variations in matter density in early universe.

Galaxy collisions

Interactions between galaxies affecting their structures.

Spinning disk

Result of gas settling due to angular momentum.

Star formation

Process where gas condenses to create stars.

Random orientations

Halo stars' orbits lack uniform directionality.

Early Universe

Time shortly after the Big Bang when galaxies formed.

Numerical simulations

Computer models predicting galaxy interactions and formations.

Galaxy evolution

Changes in galaxies over cosmic time scales.

Deep observations

Techniques revealing distant galaxies at various ages.

Newton's Law of Gravity

Describes gravitational attraction between masses.

Galaxy Collisions

Interactions between galaxies, often leading to mergers.

Elliptical Galaxy

Galaxy type formed from merging spiral galaxies.

Spiral Galaxy

Galaxy with a rotating disk and spiral arms.

Star Formation Bursts

Rapid star creation triggered by galaxy collisions.

Stellar Orbits

Paths stars follow around a galaxy's center.

Shells of Stars

Remnants of past galaxy collisions observed in ellipticals.

Galaxy Clusters

Dense regions in space where galaxies are closely packed.

Nature vs. Nurture Models

Theories explaining galaxy formation through inherent traits or environment.

Starburst Galaxies

Galaxies forming stars rapidly, depleting gas in <1 billion years.

Galactic Wind

Outflow of gas driven by supernova explosions.

Supernova Explosions

Catastrophic star deaths releasing immense energy.

Quasars

Highly luminous objects resembling stars, emitting across wavelengths.

Luminosity Variability

Brightness changes in quasars occurring over days.

Redshifted Spectra

Indicates large distances and rapid movement away from Earth.

Quasi-Stellar Object (QSO)

Another name for quasars, indicating star-like appearance.

Galactic Fountains

Gas outflows from galaxies due to supernova activity.

Elliptical Galaxy Characteristics

Random stellar orbits and often found in clusters.

Galaxy Formation Evidence

Observations supporting theories of galaxy collisions.

Hot Gas X-ray Emission

X-rays emitted from gas heated by supernovae.

Energy Source of Quasars

Energy emitted from regions smaller than solar system.

Galaxy Collision Outcomes

Spiral galaxies merging typically form elliptical galaxies.

Active Galactic Nucleus

Bright center of a galaxy with high energy.

Quasar

Most luminous type of active galactic nucleus.

Radio Galaxy

Galaxy with active nucleus emitting radio waves.

Cygnus A

Example of a powerful radio galaxy.

Centaurus A

Another notable radio galaxy with active nucleus.

Luminosity

Brightness of an object, can exceed 10^12 LSun.

Accretion Disk

Disk of gas spiraling into a black hole.

Supermassive Black Hole

Black hole with mass millions to billions of solar masses.

Energy Ejection

Active galactic nucleus ejects plasma at light speed.

Gravitational Potential Energy

Energy from matter falling into a black hole.

Kinetic Energy

Energy of motion, converted from gravitational energy.

Thermal Radiation

Heat emitted as radiation from heated matter.

Mass-Energy Conversion

Process converting mass into energy (E=mc²).

Jets of Plasma

Streams of charged particles ejected from active nuclei.

M87

Galaxy with a notable active nucleus and supermassive black hole.

Galaxy Evolution

Development of galaxies and their central black holes.

Protogalactic Clouds

Gas clouds studied through quasar light absorption.

Absorption Lines

Spectral lines indicating gas presence between Earth and quasars.

Expansion of the Universe

Galaxies moving away from Earth at varying speeds.

Black Hole Mass Relation

Central black hole mass relates to galaxy bulge mass.

Dormant Active Nuclei

Inactive supermassive black holes in many galaxies.

Quasar Spectra

Light spectra from quasars revealing cosmic information.