l>Galaxy classification Elliptical galaxies are numbers 1, 3, 5, and 8. Ellipticalgalaxies are redder than spirals, tri-axial in shape, and also devoid ofdust clouds. "Tri-axial" implies that they are football-shaped yet havedifferent values for their length, width, and height. A true footballis bi-axial, bereason it has actually the same width and elevation. Spiral galaxies are number 2, 4, 6, and also 7. Spiral are bluer thanellipticals, are round and also thin favor a compact disk, and also have visuallyobvious dust clouds. Elliptical galaxies are red. All galaxies are the color of theirbrightest stars. In fact, 99% of a galaxy"s light is emitted by thebrightest 1% of the stellar population current. Lack of dust cloudsimplies that star formation has actually ceased in these galaxies, long enoughago that tright here are no blue primary sequence stars (OB types). The coloris overcame by cool huge stars of luminosity course I. These starsare red. Because of this ellipticals are red. Spiral galaxies are blue. They have on-going star formation.Their shade is conquered by blue primary sequence stars, OB forms. Only spirals have young stars. OB kind stars have very shortlifetimes, so ALL OB type stars are necessarily young objects. OBkind stars are blue. Only spirals are blue. Because of this, only spiralshave actually young stars. Spiral stars also contain a organize of older stars. In fact, lowmass stars are created preferentially over high mass stars, so that anygalaxy has actually its total mass of stars overcame by low mass, long-livedstars. Dust manifests itself as dark blotches throughout the face of agalaxy. In galaxy #2, dust is seen as the dark patches within thepinwheel-shaped, or spiral, arms of bright emission. In galaxy #6(the "Andromeda"), dust is seen as a dark oval-shape lane appearing onone side (the close to side) of the galaxy. In galaxy #7 (the"Sombrero"), the dust shows up as a horizontal stripe across one side(the near side) of the galaxy. New stars develop from gas and also dust clouds. Therefore a galaxy thatis enduring energetic star development contains most gas. Spirals have actually an numerous gas supply, for two reasons: (i) dustacsuppliers gas clouds, and we have visual evidence for dust in spiralgalaxies, and (ii) spirals are blue, indicating new stars, indicatingthe visibility of gas. Only spirals contain both O and M type stars. All galaxiescontain M form stars. Only galaxies via active star formationcontain the short-lived O type stars. Ellipticals are made up of the cooler major sequence and giantstars, yet tright here absolutely exist G and also K kinds as well as M forms. Nogalaxy consists of exclusively M forms. Spirals contain O form stars, but other forms as well. No galaxycontains exclusively O kind stars. Agree via Student 2. The mistake made by Student 1 is notunderstanding that stars form in groups through all colors represented fromblue stars to red stars. The mistake made by Student 3 concerns thestatement that "red giants live brief lives". Key sequence stars arecontinually evolving to the red huge phase and also rearea any red giantstars that might have actually progressed better to the mass loss stage. Hubble"s proposed evolutionary sequence have the right to not be correct.

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Agalaxy is a arsenal of stars, and also we understand that when stars evolvethey end up being even more red. Thus, because no new stars form in anelliptical galaxy then ellipticals end up being more red as they age, indirect contradiction to Hubble"s proposal.