Galaxy Formation Quiz

Galaxy Overview

• Galaxies are vast collections of stars, planets, gases, dust, and other cosmic matter bound by gravity.
• An estimated 200 billion galaxies exist in the universe, varying in size from a few light-years to several hundred thousand light-years in diameter.
• A light-year equals approximately 5.8 trillion miles or 9.4 trillion kilometers, measuring the distance light travels in one year.

Galaxy Formation

• The widely accepted model posits that galaxies form from dense clouds of dust and cosmic matter that rotate and collapse under gravity into a protogalaxy.
• As the protogalaxy spins, small density fluctuations can lead to the creation of solar nebulae or protostars.
• The solar nebular theory explains the formation of Earth's solar system, where rotating matter shapes into a disk with a centralized concentration giving rise to a star, while remaining material forms planets and satellites.

Types of Galaxies

• Three main types of galaxies have been identified: elliptical, spiral, and irregular, primarily differentiated by their shapes.

Elliptical Galaxies

• Elliptical galaxies are believed to be among the oldest and most evolved, constituting about 33% of all galaxies.
• They exhibit either spherical or elongated shapes, characterized by older stars that have depleted gas and dust, making them appear dim.
• Stars in elliptical galaxies rotate in random orbits, leading to a lack of significant dust, which can cause them to resemble a single large star due to uniform light emission.
• Some ellipticals contain black holes at their center, contributing to the scarcity of dust and gas.

Spiral Galaxies

• Spiral galaxies have a distinct pinwheel shape with a central disk from which spiral arms extend.
• They can be classified as normal or barred; barred spirals feature a central bar of stars.
• The Milky Way is an example of a spiral galaxy and represents approximately 60% of all galaxies.
• Active star formation makes spiral galaxies appear bright and relatively young compared to elliptical counterparts.

Irregular Galaxies

• Irregular galaxies lack a distinct shape and are characterized by a significant presence of interstellar gases.
• They contain a mix of both young and old stars and are often formed from galaxy collisions or other chaotic stellar events.

Comparison of Galaxy Types

• Elliptical galaxies have either spherical or cucumber-like shapes versus the disk and arms of spiral galaxies.
• Stars in elliptical galaxies are older and dimmer, while spiral galaxies host younger and brighter stars.
• Irregular galaxies differ from both types by their undefined shape and the coexistence of both old and young stars.