Lectures 20 & 21: Galaxies in the Universe

Spiral Galaxy

Galaxy type with prominent spiral arms. Milky Way is this type of galaxy. Groups of galaxies (few dozen).

Elliptical Galaxy

Galaxy type with all spheroidal component, no disk component. Almost no star formation. Huge clusters of galaxies (100-1000 galaxies)

Irregular Galaxy

Galaxy with no defined shape. Very active star formation but less stars because younger.

Disk Component

Region with stars of all ages and gas clouds.

Spheroidal Component

Region with old stars, bulge, halo, few gas clouds.

Luminosity

Total amount of light emitted by a star.

High Mass Stars

Stars that are blue-white and short-lived.

Low Mass Stars

Stars that are red-yellow and long-lived.

Stellar Population Ages

Becomes more red-yellow since high-mass stars die and low-mass stars remain.

Barred Spiral Galaxy

Spiral galaxy with a bar structure across bulge.

Density Wave

Phenomenon causing star and gas concentration.

Lenticular Galaxy

Intermediate (between spiral and elliptical) galaxy type with large bulge. Like spiral galaxy but much less dusty gas.

Motions of Stars

Movement patterns in bulge and disk components.

Hubble Deep Field

Deepest image showing distant galaxies, 1996.

Hubble Ultra Deep Field

Extended observation revealing more galaxies, 2003.

COSMOS Survey

Large-scale astronomical survey of the universe.

Cosmology

Study of universe's structure and evolution.

Cosmological Distance Ladder

Step-by-step method for measuring galaxy distances. Method using multiple techniques to measure distances.

Parallax

Method for measuring nearby star distances.

Standard Candle

Object whose luminosity we can determine without measuring its distance.

Distance Formula

Distance = Luminosity / (4π x Brightness).

Area of Sphere

Calculated as 4π (radius)².

Andromeda Galaxy

Nearest spiral galaxy to the Milky Way.

Large Synoptic Survey Telescope

Upcoming project for extensive astronomical surveys.

Exposure Time

Duration of observation to capture deep space images.

Cepheid variable stars

Luminous stars used for distance measurement. Can be used as standard candles.

Period-luminosity relation

Longer periods indicate greater luminosities for Cepheids.

White-dwarf supernovae

Exploding stars used as standard candles because white dwarf explodes when mass exceeds 1.4Msun. We know the exact amount of fuel for explosion so we know the luminosity.

Hubble's Law

Velocity = H0 (Hubble constant) x distance

Hubble constant (H0)

Rate of expansion of the universe.

Redshift of a galaxy

Tells distance through Hubble’s law. Distance = velocity/H0

Tully-Fisher Relation

Galaxy luminosity relates to its rotation speed.

Cosmological Principle

Matter distributed evenly on very large scales of universe. No center & no edges.

Galaxy distances

Measured using interdependent astronomical techniques.

Expansion of the universe

All galaxies moving away from each other.

Distance measurement techniques

Methods used to determine distances to celestial objects.

Galaxy rotation speeds

Speed at which galaxies rotate, influencing luminosity.

Cosmological redshift

Wavelength stretching due to universe expansion.

Lookback time concept

Understanding distance in terms of time light travels.

Age of Universe Calculation

Time = Distance/Speed