PHY122 Ch13 Slides

PHY122 Ch13 Slides - Galaxies Star systems like our Milky...

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Galaxies • Contain ~10 -1000 billion stars ( i.e. , ~10 10 -10 12 stars) • Many shapes and sizes • Star systems like our Milky Way • Varying amounts of gas and dust
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Galaxy Classification Sa Sb Sc Elliptical Galaxies Spiral Galaxies E0 = Spherical Small nucleus; loosely wound arms E1 E6 E0, …, E7 Large nucleus; tightly wound arms E7 = Highly elliptical
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Barred Spirals Some spirals show a pronounced bar structure in the center, often with the main spiral arms emerging from the ends of the bar. They are termed barred spirals: Labeled: SBa, …, SBc, analogous to regular spirals, with lower case a,b,c telling extension of arms. S0 galaxies have a disk & a nuclear bulge, but no arms, gas, dust or new star birth. Between Spirals & Ellipticals .
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Irregular Galaxies Probably result from galaxy collisions / mergers Often very active in star formation Some are small satellites of large galaxies (“Dwarf galaxies”, e.g., the Large & Small Magellanic Clouds) Large Magellanic Cloud NGC 4038/4039 The Cocoon Galaxy
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Galaxy Sizes and Luminosities Vastly different sizes and luminosities: From small, low- luminosity irregular galaxies (much smaller and less luminous than the Milky Way) to giant ellipticals and large spirals, a few times the Milky Way’s size and luminosity.
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Gas, Dust, and Star Formation in Galaxies Spirals are rich in gas and dust, with active star birth Ellipticals (also S0) are almost devoid of gas, dust, and star formation Galaxies with disk and bulge, but no dust are termed S0 S0
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Distance Measurements to Other Galaxies a) Cepheid method: Observe a Cepheid variable star in another galaxy. Using Period – Luminosity relation: Measure the Cepheid star’s period Find its Absolute Magnitude M v Compare to apparent magnitude m v Find its distance using b) Type Ia supernovae: The collapse and explosion of an accreting white dwarf in a binary system.
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This note was uploaded on 12/11/2011 for the course PHY 121 taught by Professor Weinstein during the Fall '08 term at SUNY Buffalo.

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PHY122 Ch13 Slides - Galaxies Star systems like our Milky...

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