Lecture_17

Lecture_17 - The Hubble Ultra Deep Field a very A UNIVERSE...

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1 A UNIVERSE OF GALAXIES A UNIVERSE OF GALAXIES Islands of Stars • Our Goals for Learning • What are the three major types of galaxies? • How are galaxies grouped together? We have learned that the Sun is a member of a huge assembly of over 100 billion stars called a galaxy. Our galaxy is a flattened disk-shaped collection of stars with a diameter of 100,000 lightyears. Galaxies are the building blocks of the Universe. The Hubble Ultra Deep Field – a very long exposure showing the faintest and most distant galaxies. Spiral Galaxy Elliptical Galaxy Hubble Ultra Deep Field Elliptical Galaxy Spiral Galaxy Spiral Galaxy Elliptical Galaxy Irregular Galaxies Hubble Ultra Deep Field Elliptical Galaxy Spiral Galaxy
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2 Barred Spiral Galaxy A second kind of spiral galaxy … Blue-white color indicates ongoing star formation Red-yellow color indicates older star population Disk Component: stars of all ages, many gas clouds Spheroidal Component: bulge & halo, old stars, few gas clouds Thought Question Why does ongoing star formation lead to a blue-white appearance? A. There aren’t any red or yellow stars B. Short-lived blue stars outshine others – remember the H-R diagram; these stars are very luminous compared to less massive main sequence stars C. Gas in the disk scatters blue light Spheroidal Component: few gas clouds Disk Component: stars of all ages, many gas clouds WHAT MAKES UP OTHER GALAXIES? This galaxy has a very large spheroidal component of stars
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3 Elliptical Galaxy Red-yellow color indicates older star population Elliptical galaxies are characterized by an all spheroidal star component, virtually no disk component, and therefore no current star formation. Irregular Galaxy
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Lecture_17 - The Hubble Ultra Deep Field a very A UNIVERSE...

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