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Lecture 4

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PCS 181
Margaret Buckby

Class 7 Globular Clusters A globular cluster is a spherical distribution of ~10 to 10 stars. Typically only a few hundred light years across…. Density is 0.4stars/pc to 1000 stars/pc 3 Formed early in the life of a galaxy and contain the oldest stars known. Follow RANDOM paths through their home galaxy = do NOT move ~ circularly in the plane (disk) of the galaxy as most stars do. They are found above, below and within their galaxy. V=H d0 D=V/H 0 H 0 V/d The Hubble Classification System - Spiral (S) - Barred Spiral (SB) - Ellipticals (E) - Irregulars (Irr) - See handout for characteristics of each type You can assist the SLOAN Galaxy Survey Galaxy Zoo: Hubble Color of Galaxies - The color of galaxy is the sum of color contributions from its stars - Ellipticals: reddish-orange from old stars - Spirals: central bulge is reddish-orange from old stars there. - Spiral arms are blue from the presence of hot young stars (forming from the gas and dust in the arms) - Irregulars: contain largest amounts of dust/gas are the blue-est galaxies known and support the most active star birth What are the blue-est galaxies? Irregulars test question ***Know the handout for the Midterm test #1*** 30 multiple choice questions 25 conceptual and 5 math questions Luminosity Luminosity = L = Total energy emitted each second Equation for L is on formula sheet R is radius T is temperature Approximate Mass of a Galaxy In the luminosity, L, of a galaxy is n times the luminosity of the Sun, nL o, Then, a rough estimate of its mass is n times the mass of the Sun, nM o The Milky Way is estimated to have a luminosity of L MW ~ 1 x 10 L o Provide a rough estimate of its mass M MW ~ (1 x 10 ) (1.99 x 10 kg) 41 M MW ~ 2 x 10 kg **need to know multiply luminosity of galaxy to mass of the sun Mass range of galaxies 5 13 Galaxy masses range from ~1 x 10 M to o1 x 10 M . o Our galaxy, the Milky Way, has a mass of ~5.8 x 10 M1 o 42 =1.2 x 10 M o Morphology of Spirals Spirals spin faster than ellipticals -> Higher angular momentum, L = mvr. Born in a turbulent environment??? Spirals form/contract slowly and have gas/dust to support ongoing star birth. Spiral structure is extremely delicate and would be destroyed in a collision with another massive galaxy. Obvious spirals have NOT undergone major collisions. Morphology of Ellipticals Ellipticals rotate more slowly than spirals. Born in a quiet environment??? Ellipticals contracted fast
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