Types of Galaxy Flashcards

Study Notes

What is a Galaxy?

A galaxy is a gravitationally bound collection of stars, gas, and dust.
Our galaxy contains around 100 billion stars.
Galaxies are usually isolated but can interact with nearby galaxies.
They represent the main visible components of the Universe.

Major Galaxy Types

Galaxies are primarily categorized into three major types:
- Spirals
- Ellipticals
- Irregulars

Spiral Galaxies

Characterized by a rotating disk with prominent spiral arms.
Spiral arms are abundant in young, hot, blue stars (Population I stars).
Rich in gas and dust, serving as regions for new star formation.
The central region, or bulge, contains older red stars (Population II stars).
Some spiral galaxies exhibit a barred structure where arms extend from a central bulge.

Elliptical Galaxies

Composed predominantly of red stars (Population II stars) and some older Population I stars.
Display smooth variations in light intensity with little gas and dust.
Have low organized rotation and can be found in giant or dwarf forms.

Irregular Galaxies

Lacking a regular structure and shape.
Rich in gas, dust, and blue stars, containing a mixture of Population I and II stars.
Typically smaller in size compared to other galaxy types.

Galaxy Classification

Galaxies are classified using Hubble's tuning fork diagram.

Classification of Elliptical Galaxies

Elliptical galaxies (E) are classified based on their apparent ellipticity, determined by the formula (10(a-b)/a).
Apparent ellipticity varies with the viewing angle, resulting in classifications like E0, E3, E6, etc.

Classification of Spiral Galaxies

Spiral galaxies (S) are classified by the size of the bulge, amount of gas and dust, and tightness of spiral arms.
Sa galaxies have large bulges, tight spiral arms, and limited gas and dust.
Sc galaxies feature small bulges, loose spiral arms, and significant amounts of gas and dust.
Sb galaxies are intermediate between Sa and Sc classifications.
Barred spirals (SB) have an equivalent classification ranging from SBa to SBc, with variations determined by the prominence of the bulge and bar.

S0 Galaxies

S0 galaxies are transitional between elliptical (E7) and spiral (Sa or SBa) galaxies.
They contain a disc, bulge, and elliptical component but lack obvious spiral arms.
Also referred to as lenticular galaxies.

General Classification Notes

Galaxies can be divided into spirals, ellipticals, or irregulars.
Hubble's tuning fork diagram is a helpful classification tool but does not imply an evolutionary sequence.
Spirals and irregulars contain gas, dust, and young blue stars, whereas ellipticals are primarily composed of older red stars.

Description

Explore the fascinating world of galaxies with these flashcards. Learn about what defines a galaxy and discover the three major types: spirals, ellipticals, and irregulars. Perfect for anyone looking to enhance their knowledge of the universe.