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hw15.pdf - PHYS 3315: Astrophysics and Cosmology - FA 2020...

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PHYS 3315: Astrophysics and Cosmology - FA 2020Homework 15(12/1/2020)1.At the center of our Milky Way Galaxy, there is a supermassive black hole.Infrared observations show that a star orbits around this black hole onceevery 14.5 years on an elliptical orbit with a semi-major axisa= 920 AU.Estimate the mass of this black hole at the Galactic center.
2.The Sun moves around the Galactic center in a nearly circular orbit with theradiusR0~ 8 kpc at the orbital velocityv0~ 220 km s−1. The total mass of theGalaxy within the Sun’s orbit isMG. The observed Galactic rotation curveshows an orbital velocity of starsv~ 270 km s−1at near the outer boundaryof the visible Galactic disk (d~ 16 kpc from the Galactic center). Calculate thetotal Galactic mass between the Sun’s orbit and the outer boundary of theGalactic disk in units ofMG.
3.UsingCepheid variables, Edwin Hubble measured the distance to the
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Winter
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galactic center

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