Post on 05-Jan-2016
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AnnouncementsHomework #10: due today
Solutions and study guides will be posted online.
Final Exam scheduled for May 22nd @ 12:15. Bring a scantron form 882-EZ
Need extra help? Come to SCI 242 on Thursday, 5/17, at either 10AM or 3PM.
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Stellar Remnants:White Dwarfs, Neutron Stars, & Black Holes
(Chp. 14)
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Black Holes:• Progenitor mass: > 10-20 MSun
• Schwarzscild Radius• Event Horizon• What is the event horizon for a 1 MSun object?• Observational Evidence for the existence of BH’s
• X-Ray Binaries• Center of the Milky Way
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Eclipsing X-Ray Binaries
Accretion disk emits x-ray radiation
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Orbit of S2: P=15.2 years; a=900 AUMass according to Kepler’s laws: 3.5x106 MSun!
Luminosity: below detection thresholdClosest approach: 17 light-hours
Mass of central object: 3 Million MSun!!
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The Milky Way Galaxy(Chp. 15)
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Looking up at the sky at night, we can see that the Sun is one of (at least) thousands of stars. We also see that the stars in the sky are not uniformly spread out.
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Very thin (100-1000 pc)
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Milky Way
NGC 891
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NGC 1232
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Angle between Solar System plane and Galactic plane
62 degrees
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Artist’s depiction of solar system seen from Sedna
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• DiskDisk– Distribution of stars, gas, and dust with a diameter Distribution of stars, gas, and dust with a diameter
of about 30 kpc (100,000 light-years) and plane of about 30 kpc (100,000 light-years) and plane tilted with respect to Earth’s orbit around Suntilted with respect to Earth’s orbit around Sun
– Rotation with all objects circling in the same Rotation with all objects circling in the same directiondirection
– High density of stars near center (10 million stars High density of stars near center (10 million stars per cubic light-year) to low density farther out per cubic light-year) to low density farther out (0.003 stars per cubic light-year at Sun)(0.003 stars per cubic light-year at Sun)
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• HaloHalo– Roughly spherical region (disk embedded)Roughly spherical region (disk embedded)– Contains mainly old stars, such as globular Contains mainly old stars, such as globular
clustersclusters
• BulgeBulge– Flattened collection of stars surrounding dense Flattened collection of stars surrounding dense
core of galaxycore of galaxy– About 1/3 the diameter of the galaxyAbout 1/3 the diameter of the galaxy
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Spiral Density Wave: galactic traffic jam
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Milky Way:• Herschel’s star counts• Shapley’s work with globular clusters• size (50,000 pc across; 100-1000 pc thick)• location of Sun (8,000 pc from center)• Components: bulge, disk, halo• Motion
• bulge versus disk• direction of Sun’s motion with respect to spiral arms
• Angle between ecliptic and Milky Way• Spiral Structure
• “traffic jam”• young stars found in spiral arms
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4 billion miles from home…
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Earth, Moon, and Jupiter as seen from Mars
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The Pale Blue Dot