PHY122 Ch 13 Galaxies

PHY122 Ch 13 Galaxies - Astronomy Chapter 13: Galaxies Star...

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Astronomy Chapter 13: Galaxies Star systems like our Milky Way contain a few thousand to tens of billions of stars, as well as varying amounts of gas and dust; large variety of shapes and sizes - Astronomers divide galaxies into three classes – Elliptical: round or elliptical, contain no visible gas and dust and have few or no hot, bright, blue stars (cannot make new stars) and therefore have a reddish tint Classified with a numerical index ranging from 1 – 7; E0’s are round and E7’s are highly elliptical. formulaa Spiral: contain a disk and spiral arms; have halos (though not visible and ); spirals contain gas and dust and hot, bright O and B stars (star formation is occurring, especially along spiral arms). Some of the newborn stars are massive, hot, and blue, and that gives the spiral arms a blue tint The halo and nuclear bulge of a spiral galaxy usually lack gas and dust and contain little star formation. The halos and nuclear bulges have a reddish tint because they lack hot, blue stars. Sa galaxies have larger nuclei, less gas and dust, and fewer hot bright stars; Sb galaxies are intermediate. Barred spiral galaxies – 2/3 of all spiral galaxies; classified SBa, SBb, and SBc. They have an elongated nucleus with spiral arms springing from the ends of the bar structure in the center. Our own galaxy is barred spiral. Galaxies with an obvious disk and nuclear bulge but no visible gas and dust and few to not bright, hot stars are classified as S0 Irregular : no obvious shape; chaotic mix of gas, dust, and stars with no obvious nuclear bulge or spiral arms; (ex- Magellanic clouds) Often a result of galaxy collisions/mergers Very active star formation (“starburst galaxies” Some: small (“Dwarf galaxies”) satellites of larger galaxies
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Spirals are rich in gas and dust, Ellipticals are almost devoid of gas and dust, and galaxies with a disk and bulge but no dust are termed S0 - Galaxies are so distant astronomers measure their distances in megaparsecs – millions of parsecs. One Mpc = 3.26 million ly (or 3 x 10 19 km) - Astronomers find the distance to galaxies using distance indicators
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PHY122 Ch 13 Galaxies - Astronomy Chapter 13: Galaxies Star...

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