AST 105 1st Edition Lecture 16Outline of Previous Lecture I. Schwarzschild Radius II. No Hair Theorem III. Roy KerrIV. Falling into a Black Hole a. Victims view pointb. Onlookers view pointV. Hawking Radiation VI. Summary on Worm HolesVII. Galaxies Outline of Current Lecture I. Edwin HubbleII. Milky Way Galaxy a. Spiral StructureIII. Galactic CenterEdwin Hubble- 1923- he took photographs of a distant object, M31- Examined his photographic plates and noticed that Cepheid’s existed on M31 We recall that Cepheid’s have a period-luminosity relation- Looking at Cepheid’s in M31 by observing the period (days) from bright to dim back to bright, he could determine the absolute magnitude (M)…and he also knew the apparent magnitude (m) He could then determine the distance in parsecs M31 was 2.2 million light years away- Milky Way in only 100,000 LY’s across- M31 was another galaxy - 1924- Hubble presents these resultsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Milky Way Galaxy - Rotating disc of matter Spiral structure- Spiral “arms”- In the center is the galactic nucleus (galactic bulge, bulge)- Our solar system is about 27,000 LY’s from center- Large quantities of dust/particles lie in the plane Thus, our view of the galaxy is obscured - We are able to locate the center of the galaxy by examining the globular clusters - The globular clusters orbit the center of the galaxy but they do not lie in the galactic planeSpiral Structures of Milky Way - Particles have spin - In hydrogen atom, the electron and the proton can have either parallel spin vectors or opposite spin vectors Photon has a wavelength of 21 cm - Using Doppler shift techniques, we examine the 21 cm protons map out the velocity profiles of Milky Way Galaxy - Using careful measurement allows us to understand the structure Spiral arm structure of the Milky Way Galaxy - There are about 1011 stars in the Milky Way Galaxy Galactic Center - In the center of the Milky Way is the bulge Diameter is about 20,000 Ly’s- A planet in the bulge will never experience night Star light from surrounding stars equal to 200 full moons - Analyzing the hydrogen in the bulge, we can calculate the required mass to confine the hydrogen into the tight orbit- Mass of the center (Mcenter) of our galaxy is about 2.5 million solar masses (2.5Msun)- Super massive black hole at our center! This is supported by: X-ray production, positron production, synchrotron radiation o Synchrotron Radiation High speed electrons trapped Circular pathsRadiate
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