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Galaxies

Explore the composition and structure of the Milky Way galaxy, including the stars in the Herschel band, the presence of dark matter, and the classification of galaxies. Learn about the rotation speed, types of galaxies, galaxy collisions, and the discovery of quasars.

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Galaxies

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  1. Galaxies Where we live: Milkyway Galaxy Orion Arm System of Sol Third Planet

  2. Herschel Band of light stretching in the night sky was known to the ancients. Methodical study of the sky (1785). Divide into little squares and count the number of stars. More stars on the diagonal. Sun at the center.

  3. Milkyway Galaxy 50,000 ly radius halo (non-luminous matter) 1,000 ly nuclear bulge Average size galaxy Spiral galaxy with 3 ½ arms. Perseus, Cygnus, Carina, Orion 80,000 lightyears diameter

  4. Center of our galaxy • At the center of our galaxy there is a super massive blackhole. • The size of this blackhole is estimated to be 4 million Solar masses.

  5. Size of the galaxies Copernicus  Earth is not the center of the Solar system Harlow Shapley  Sun is not the center of the Milkyway galaxy. Cepheids and RR Lyrae are at the end of their lives and they change their brightness in a well known way. As their brightness is known they can be used as standard candles to determine distances. Shapley used 93 variable stars to measure the distances in our galaxy. And proved that we are not at the center of our galaxy.

  6. Rotation Speed Our galaxy rotates around its center. The sun revolves around the galactic center every 200,000,000 years. The density of stars increase when we go closer to the galactic center. The mass of the stars in a galaxy can be calculated by the revolution speed of the stars around the galactic center. The more mass, the higher should be the revolution speed. However…

  7. Dark Matter Sun revolves around the galactic center much faster than the visible matter of the galaxy suggests  There is more mass in the galaxy than we can see DARK MATTER Not just a little to make the calculations correct, but around 80-90% of Milkyway’s mass in dark matter.

  8. Types of Galaxies Classification made by Edwin Hubble in the 1920s. Three types of galaxies: Elliptical, Spiral and Irregular Spirals are further divided into regular spirals and barred spirals. These groups are further divided among themselves depending on how large the nucleus is (spirals) or how spherical they are (elliptical).

  9. Other Galaxies 10th century astronomer Al-Sufi  M31 – Andromeda galaxy, Little Cloud Magellan  Clouds in the Southern Sky  Magellanic Clouds Messier  1781 Catalog of nebulous objects (M31) Herschel  New General Catalog (NGC3034 = M82) Big question: Where are they located?? Shapley (no galaxies) – Curtis (galaxies) debate (1920) Hubble and Humason resolved in 1932.  discovered many Cepheid variables in the Andromeda galaxy  they are not in this galaxy, far far away.

  10. Elliptical Galaxies M32: Satellite of Andromeda M87: Virgo cluster M110: Satellite of Andromeda Leo I: Local group

  11. Spiral Galaxies NGC 2997 NGC 3351 = M95 Triangulum Galaxy (M33) in our local cluster NGC 1365

  12. Irregulars Small Magellanic Cloud Large Magellanic Cloud

  13. Clusters Galaxies love to cluster together. Hercules cluster: A poor cluster Milkway is part of a poor cluster called the Local Group. Coma cluster: A rich cluster

  14. Galaxy Collisions If there is clustering because of gravitational interactions, there is bound to be some collisions. BTW, we are going to collide with the Andromeda galaxy in a few hundred million years.

  15. Hubble’s Law In 1931, Hubble and Humason discovered that more distant galaxies are moving faster away from us.

  16. Quasars Very difficult to distinguish from regular stars in the sky. However, they have a very large red-shift meaning that they are very far away (Hubble’s Law). They are also changing their luminosity very rapidly, we can estimate their sizes. Optical observations confirm that they are at the center of galaxies far away. The combination of all this information tells us that: The size of a quasar is less than a lightyear in diameter. They are about 1000 times brighter than our galaxy. They can be at distances about 10 billion lightyears away, but there are no quasar located farther away than that.

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