Galaxy Classification PDF

COLLEGE OF SCIENCE Department of Mathematics and Physics Handout on Galaxy and Milky Way Galaxy Galaxies, vast collections of stars, gas, dust, and dark matter, are Classification classified into different types based on their shapes and structu...

COLLEGE OF SCIENCE Department of Mathematics and Physics Handout on Galaxy and Milky Way Galaxy Galaxies, vast collections of stars, gas, dust, and dark matter, are Classification classified into different types based on their shapes and structures. The most widely used system is Edwin Hubble's classification, which includes: Elliptical Galaxies (E): These have an oval or spherical shape with little to no structure. They range from nearly circular (E0) to highly elongated (E7). Elliptical galaxies contain older stars and have little gas or dust, making them relatively inactive in terms of star formation. o M87 (NGC 4486): A giant elliptical galaxy located in the Virgo Cluster. It's known for its large size and the presence of a supermassive black hole at its center, which powers a massive jet of relativistic plasma. o M49 (NGC 4472): Another large elliptical galaxy in the Virgo Cluster, containing a significant population of old stars and little gas or dust. Spiral Galaxies (S): These have a flat, disk-like structure with a central bulge and spiral arms. They are further divided into: o Normal Spirals (S): Arms extend from the central bulge. ▪ Andromeda Galaxy (M31): A classic spiral galaxy and the nearest spiral galaxy to the Milky Way. It's on a collision course with the Milky Way, with a predicted merger in about 4.5 billion years. ▪ Whirlpool Galaxy (M51, NGC 5194): A face-on spiral galaxy that is interacting with a smaller companion galaxy, NGC 5195. It's famous for its well-defined spiral arms. o Barred Spirals (SB): Arms extend from a bar of stars that runs through the central bulge. Spiral galaxies are rich in gas and dust, supporting active star formation. ▪ Milky Way: Our home galaxy, with a central bar structure and spiral arms extending from the ends of the bar. ▪ NGC 1300: A well-known barred spiral galaxy located about 61 million light-years away in the constellation Eridanus. It features a prominent bar structure and beautifully defined spiral arms. Irregular Galaxies (Irr): These lack a defined shape and structure. They are often rich in gas and dust and can form stars rapidly. These galaxies may have been disrupted by gravitational interactions with other galaxies. o Large Magellanic Cloud (LMC): A satellite galaxy of the Milky Way, the LMC is an irregular galaxy containing regions of active star formation. It's one of the closest galaxies to the Milky Way. o NGC 4449: An irregular galaxy in the constellation Canes Venatici. It shows signs of recent star formation Galaxy and Milky Way | Prepared by MROBalmeo  and is part of a galaxy group that is interacting with other galaxies. Distribution of Galaxies are not randomly scattered throughout the universe but Galaxies are found in vast structures known as large-scale structures. These include: Galaxy Groups and Clusters: Groups contain a few to dozens of galaxies bound by gravity, while clusters can have hundreds to thousands of galaxies. The Milky Way is part of the Local Group, a collection of around 54 galaxies. Superclusters: Collections of galaxy clusters. Our Local Group is part of the Virgo Supercluster. Cosmic Web: On the largest scales, galaxies and galaxy clusters are distributed along filaments and sheets, separated by vast voids, creating a web-like structure. How Galaxies are Galaxies formed in the early universe from regions of higher-than- Formed average density in the primordial matter. Hierarchical galaxy formation is a widely accepted model that suggests small structures merged over time to form larger ones. The process includes: Gas Cooling and Collapse: Regions of cold gas collapsed under gravity to form stars, creating the first small galaxies. Mergers: Smaller galaxies collided and merged to form larger galaxies. Accretion of Material: Galaxies grew by accreting gas and smaller galaxies from their surroundings. How Galaxies Galactic evolution is influenced by: Evolve Mergers and Interactions: Galaxies merge, which can trigger bursts of star formation and reshape galaxies. For example, a spiral galaxy can become an elliptical galaxy through mergers. Star Formation: Over time, star formation consumes gas, leading to less active galaxies. The balance between gas accretion and star formation determines a galaxy’s evolution. Feedback Mechanisms: Supernova explosions and active galactic nuclei can expel gas, affecting the star formation rate and future evolution of the galaxy. Galaxy and Milky Way | Prepared by MROBalmeo Milky Way Type: The Milky Way is a barred spiral galaxy. Size: It spans about 100,000 light-years across. Structure: The Milky Way consists of a central bulge, spiral arms, and a halo of stars and dark matter. Star Count: Contains around 100-400 billion stars. Location: Our Solar System is located in the Orion Arm, about 26,000 light-years from the galactic center. Mass: estimated to be around 1 trillion solar masses. However, most of this mass is in the form of dark matter, an invisible substance that does not emit light but exerts gravitational influence. The visible matter, including stars, gas, and dust, constitutes only a small fraction of the galaxy's total mass. Galactic Center: located in the constellation Sagittarius. It hosts a supermassive black hole called Sagittarius A*, with a mass of about 4 million times that of the Sun. Surrounding the black hole is a dense region of stars, gas, and dust. The Galactic Center is also a source of intense radio and X-ray emissions, and its study provides crucial insights into the behavior of matter in extreme gravitational environments. Prepared by: Mary Rose O. Balmeo CLSU-DMP Galaxy and Milky Way | Prepared by MROBalmeo