Astronomy group work introduction to astonishing
- 2. Introduction to other Galaxies • Classification and Features of Elliptical and Spiral Galaxies ● Hubble's Tuning Fork diagram
- 3. Introduction to other Galaxies ● Galaxy morphological classification is a system used by astronomers to divide galaxies into groups based on their visual appearance. ● There are several schemes in use by which galaxies can be classified according to their morphologies, the most famous being the Hubble sequence, devised by Edwin Hubble and later expanded by Gérard de Vaucouleurs and Allan Sandage. ● However, galaxy classification and morphology are now largely done using computational methods and physical morphology.
- 4. Hubble sequence ● The Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1926. ● It is often known as the “Hubble tuning-fork” because of the shape in which it is traditionally represented. Hubble's scheme divides galaxies into three broad classes based on their visual appearance
- 6. Elliptical Galaxies • - Form: Ellipsoidal shape, from E0 (circular) to E7 (elongated). • - Features: • Found at the centers of large clusters. • Contain up to 10 million solar masses. • Composed of old stars; no active star formation. • Account for one-third of all galaxies.
- 7. ● An elliptical galaxy is a type of galaxy with an approximately ellipsoidal shape and a smooth, nearly featureless image. They are one of the three main classes of galaxy described by Edwin Hubble in his Hubble sequence. ● Most elliptical galaxies are composed of older, low- mass stars, with a sparse interstellar medium, and they tend to be surrounded by large numbers of globular clusters. Star formation activity in elliptical galaxies is typically minimal
- 9. Spiral Galaxies • - Form: Flattened spiral structure with arms extending from the nucleus. • - Classification: • - Hubble's types: SO (lenticular), Sa, Sb, Sc. • - Barred spirals: SBa, SBb, SBc. • - Features: • - Central nucleus: Yellow-orange from old stars. • - Spiral arms: Blue from young, massive stars. • - Example: Whirlpool Galaxy (M51).
- 10. ● Spiral galaxies are named by their spiral structures that extend from the center into the galactic disc. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because of the young, hot OB stars that inhabit them.
- 11. Structure of Spiral Galaxies 1.The stellar bulge ● A bulge is a large, tightly packed group of stars. The term refers to the central group of stars found in most spiral galaxies ● Using the Hubble classification, the bulge of Sa galaxies is usually composed of Population II stars, which are old, red stars with low metal content. ● In contrast, the bulges of Sc and SBc galaxies are much smaller and are composed of young, blue Population I stars
- 12. 2. Spiral arms ● Spiral arms are regions of stars that extend from the center of barred and unbarred spiral galaxies. These long, thin regions resemble a spiral and thus give spiral galaxies their name. ● Naturally, different classifications of spiral galaxies have distinct arm-structures. Sc and SBc galaxies, for instance, have very "loose" arms, whereas Sa and SBa galaxies have tightly wrapped arms (with reference to the Hubble sequence). Either way, spiral arms contain many young, blue ● stars (due to the high mass density and the high rate of star formation), which make the arms so bright.
- 13. 3. Bar ● A bar is an elongated structure made of stars and interstellar material that stretches across the central region of some spiral galaxies, connecting the spiral arms. ● Bars are composed mainly of older stars, though they may also funnel gas toward the galaxy's center, fueling star formation and possibly feeding a central black hole. ● Bars act as "stellar highways," redistributing stars and gas throughout the galaxy and regulating its dynamics.
- 15. Galaxy M81 in Ursa Major ● The image shows Galaxy M81 in Ursa Major. It highlights the spiral structure with young blue stars. The center appears overexposed due to the bright core, and the colors are slightly enhanced to show details.
- 16. Hubble’s tuning fork diagram ● Hubble's Tuning Fork diagram classifies galaxies into ellipticals and spirals. Elliptical galaxies range from spherical (E0) to elongated (E7), while spirals are categorized based on the tightness of their arms. The classification was meant to study galaxy evolution.