Questions and Answers
What is a galaxy?
A galaxy is a gravitationally bound collection of stars, gas, and dust.
What are the major galaxy types?
Describe a spiral galaxy.
A rotating disc dominated by spiral arms rich in young, hot, blue stars, with a bulge at the center.
Describe an elliptical galaxy.
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Describe an irregular galaxy.
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How are galaxies classified?
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How are elliptical galaxies classified?
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How are spiral galaxies classified?
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What are S0 galaxies?
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Galaxies can be classified as either spirals, ellipticals, or irregulars.
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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.
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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.
