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Exploring Galaxies: An Astronomy Overview

Discover the universe's mysteries through tools like imaging, spectroscopy, and computational analysis. Learn about galaxy types, components like stars and black holes, and the enigmatic dark matter. Explore cosmology, the formation of solar systems, and the evolution of stars. Gain insights into active galaxies, clusters, and the expanding universe.

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Exploring Galaxies: An Astronomy Overview

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  1. Overview of Astronomy AST 200

  2. Astronomy • Nature designs the Experiment • Tools • Imaging • Spectroscopy • Computational

  3. Galaxy – Gravitationally bound aggregate of • Million to 100 billion stars • Gas and dust (10s of % by mass) • Dark Matter

  4. Properties… • Masses = million to trillion solar masses • Sizes = 30,000 to 300,000 light years • Rotation Period = 10 – 100 million years • Average Separation = 3 million light years

  5. Galaxy Types – Spiral Galaxies • Central Bulge – Old Stars • Disk – Young Stars, Gas, and Dust • Some have bars

  6. Schematic of Spiral Galaxy The Sun is approximately 28,000 light years from the center of our Galaxy

  7. Galaxy Types – Elliptical Galaxies • Old Stars • Very little Gas and Dust

  8. Galaxy Types – Dwarf Ellipticals • Masses = 10 million to 1 billion Solar Masses • There are a lot more dwarf elliptical galaxies than there are spiral or normal elliptical galaxies

  9. Galaxy Components - Stars • Powered by fusion (hydrogen helium + energy) • Stability – balance of inward gravity and outward radiation pressure • Importance – heat, light, metal production • Lots of low mass stars, fewer high mass stars, & the relative fraction may be the same for every star-forming environment

  10. Hertzsprung-Russell Diagram

  11. Stars (cont) • Lifetimes of Stars depend upon Mass (Sun = 10 billion years) • End State Depends on Mass • Average Separation of Stars 3 – 4 light years

  12. End States • Mstar < 8 Msolar - White dwarf • Mstar = 8-60 Msolar - Neutron star • Mstar > 60 Msolar - Black hole

  13. Evolution along the HR Diagram

  14. Galaxy Components - Solar Systems • Solar systems consists of objects that are gravitationally bound to stars • Our own solar system consists of 8 – 9 planets, comets, and a host of smaller objects comprised of rock and ice • Many extrasolar planets have been found recently, indicating that solar systems may be quite common

  15. Formation of Solar System Products Planets Comets, etc

  16. Our Solar System: Terrestrial & Gas Giants

  17. Formation of the Solar System

  18. Extrasolar Planets - Radial Velocities • Accuracy needed: ~10s of m s-1 or ~ 20 mph (Video)

  19. Examples -

  20. Galaxy Components – Gas • Stars form in molecular clouds • Molecular clouds can have masses of up to 1 million solar masses • Molecular gas is found in the disk regions of spiral galaxies

  21. Gas, cont. • Neutral hydrogen gas extends farther out in galaxies than the stellar disk does • We use the motion of the gas to determine galaxy masses…

  22. … and to trace interaction

  23. Components – Black Holes • Very massive stars form black holes when they die • But we also find supermassive (million to a billion solar masses) black holes at the centers of galaxies • There is a relationship between the mass of black hole in the center of a galaxy and the mass of stars in the bulge of a galaxy

  24. The Center of Our Galaxy

  25. Dark Matter • It appears that most (90%) of the mass in the universe is dark – i.e., it doesn’t emit light • Evidence – e.g., masses calculated from galaxy rotation curves • Distribution in galaxies – spherical • What is it? dead stars, black holes + SOMETHING ELSE

  26. Starburst Galaxies & Active Galaxies • Some galaxies are observed to be making new stars at 10 – 100 times that of normal spiral galaxies • Others are observed to have bright, compact nuclei which appear to be powered by mass accretion onto a central black hole

  27. We believe that activity in extreme starburst galaxies & active galaxies are mostly caused by a galaxy merger event

  28. Clusters of Galaxies • Very massive – 100 trillion solar masses

  29. Cosmology – origin and evolution of the universe • The universe is expanding – all galaxies are moving away from us • The universe was once much hotter – 3K background radiation • A lot of work has gone into finding distant galaxies in order to figure out when the first galaxies formed and how they evolve.

  30. Cosmology – origin and evolution of the universe • The universe is expanding – all galaxies are moving away from us • The universe was once much hotter – 3K background radiation • A lot of work has gone into finding distant galaxies in order to figure out when the first galaxies formed and how they evolve. 3K Cosmic Microwave Background

  31. Cosmology – origin and evolution of the universe • The universe is expanding – all galaxies are moving away from us • The universe was once much hotter – 3K background radiation • A lot of work has gone into finding distant galaxies in order to figure out when the first galaxies formed and how they evolve.

  32. Cosmological Parameters • Hubble Constant = H0 • Density of Universe = matter + DM + 

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