Classifying Galaxies Flashcards

Galaxies Overview

• A galaxy consists of billions of stars, gas, and dust bound by gravity.
• Galaxies vary significantly in size, shape, and appearance throughout the universe.

Edwin Hubble's Contribution

• Edwin Hubble classified galaxies by shape in the 1920s, emphasizing visual characteristics.
• Galaxies can be categorized into different types based on their shapes and structural features.

Types of Galaxies

• Elliptical Galaxies (E): Indicated by the letter "E" and classified from E0 to E7 based on flattening and stretching.
• Spiral Galaxies (S): Recognized by how tightly their arms wrap around the nucleus, classified as Sa, Sb, or Sc from tightly to loosely wound.
• Barred Spiral Galaxies (SB): Similar to spiral galaxies but with a bar structure; categorized as SBa, SBb, or SBc based on the openness of the arms.

Hubble Tuning Fork Diagram

• Hubble created the Tuning Fork Diagram, showcasing galaxy classifications visually, where most galaxies fit into distinct categories.

Characteristics of Galaxies

• Not all galaxies are elliptical; elliptical galaxies are merely one type among many within the broader galaxy classification.
• Irregular galaxies lack a blackhole, distinguishing them from other types.
• Variations in spiral galaxies are characterized by the size of their central bulge and the tightness of their arms.

Distinctions Among Spiral Galaxies

• Sa Galaxies: Feature a large central bulge and tightly wound arms.
• Sc Galaxies: Exhibit a smaller bulge with very loose arms.

Elliptical Galaxies vs. Galactic Halo

• Elliptical galaxies resemble the Milky Way's halo, containing mostly old, low-mass, reddish stars and disordered star orbits with limited rotation.
• Elliptical galaxies, unlike the halo, have significant amounts of very hot interstellar gas.

Local Group and Virgo Cluster

• The Local Group includes the Milky Way, Andromeda, M33, and various dwarf galaxies, spanning approximately 1 Mpc in diameter.
• The Virgo Cluster comprises about 2500 galaxies and measures around 3 Mpc across.

Galaxy Emission Types

• Normal Galaxies: Emit visible light radiation.
• Active Galaxies: Emit higher levels of radiation, including infrared and radio frequencies.

Other Galaxy Types

• Lenticular (S0) Galaxies: Feature a disk and bulge but lack spiral arms.
• Peculiar Galaxies: May originate from spirals that merged with others, altering their structure.
• Irregular Galaxies: Resemble nebulas in appearance.

Mergers and Galaxy Formation

• Mergers between small and large spiral galaxies yield larger spiral galaxies.
• Two large spiral galaxies combine to form a large elliptical galaxy.
• A mix of large and small elliptical galaxies can result in either large spirals or other structures depending on the sizes involved.

Clusters and Dark Matter

• The nearest galaxy cluster to Earth is the Virgo Cluster, which holds significant cosmic importance.
• Evidence for dark matter in galaxies is found in the consistent rotational rates maintained from the center out to the edges of galaxies.
• The nearest galaxy to Earth is Andromeda.

Test your knowledge on the classification of galaxies with these flashcards. Learn about the definitions, characteristics, and historical figures involved in astronomy. This quiz will enhance your understanding of the vastness and variety of galaxies in the universe.