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PCS 181 class 7.docx

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PCS 181
Margaret Buckby

PCS 181 PCS 181 Thursday, February-07-13 Class 7  Similarly, 3C48 quasars are known and all are extremely red-shifted  What is the distance to 3C273: d= Vr/Ho d= (4.8*10^4km/s)/(75km/s/Mpc) d= 640Mpc d= (640*10^16pc)(3.26ly) = 2.09*10^9ly d= 2 billion ly away Relativistic Velocity Equation  Consider one of the fastest, most distant quasars at Z=5.82  Since Vr = cz, is this quasar moving at 5.82 times the speed of light?  No, no material object can exceed the speed of light  For z > 0.5, we turn to relativity  Relativistic velocity formula: Vr = ((z-1)^2)-1) *c ((z+1)^2)+1)  Ex: z = 5.82 ((5.82-1)^2)-1) *c ((5.82-1)^2)-1) =(45.51) *c (47.51) =0.958*c = 96% the speed of light (3*10^8 m/s) Distance to the Quasar  If the Hubble law is valid, this quasar must be very far away  D =V/Ho = ((0.958(3*10^5km/s)) 75km/s D= 3832Mpc = 12.5*10^9ly D = 12.5 billion ly away  To see quasars over such vast (“cosmological”) distances, they must be intrinsically very bright  Quasars often emit as much energy as 100-1000normal galaxies combined  The size may be determined by a technique known as Lunar Occultation  Apparent size of a quasar: d = vt = Page 1 PCS 181  After we connect for the distance to the quasar, we find that:  QSO 3C273 was the size of a large star  How could the energy of 100-1000 galaxies be produced by an object th
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