PGCC PSC 1010 - Galaxies (25 pages)

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Galaxies



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Galaxies

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Lecture Notes


Pages:
25
School:
Prince George’s Community College
Course:
Psc 1010 - Introduction to Astronomy

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Galaxies Galaxies are clouds of millions to hundreds of billions of stars held together by their mutual gravity Often galaxies also contain enormous clouds of gas and dust from which new stars can form Galaxies can have many different shapes and sizes The distribution of galaxies across the Universe indicates that they generally appear in clusters with very large voids separating clusters from one another The Andromeda Galaxy nearest galaxy similar to our own Only 2 million light years away 1 Types of Galaxies Galaxies are classified based on general characteristics and then further subdivided based on more specific characteristics Spiral galaxies disk shaped with spiral arms winding out from the center usually have clouds of gas and dust usually have both young Pop I and old Pop II stars some spirals have a rectangularshaped bar through the central bulge and are referred to as Barred Spirals A Hubble Space Telescope view of the Whirlpool Galaxy M51 2 Types of Galaxies Elliptical galaxies are always smooth in appearance can be spherical egg shaped or flattened in shape usually have little or no gas and dust usually only contain old stars Pop II Irregular galaxies have a random distribution of stars often have large clouds of gas and dust often contain young stars Pop I 3 Galaxy Collisions galaxies were smaller in the past collisions between galaxies appear to have been common in the early Universe collisions can cause bursts of star formation as clouds of gas and dust collapse galaxies may eventually merge together forming large elliptical galaxies A Hubble Space Telescope image of the Antennae Galaxies Large streams of stars and gas are trailing off the galaxies while new stars are being formed near the center 4 5 Active Galactic Nuclei AGN Spiral or disk galaxies with nuclei that are more luminous than the rest of the stars in galaxy Spectrum of the nucleus is non stellar Luminosity of the nucleus may change over short hours months Some elliptical galaxies show



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