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Lecture 5

Introduction to Astronomy-Lecture 5 Notes!.docx

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Department
Physics
Course
PCS 181
Professor
Margaret Buckby
Semester
Winter

Description
N r C Triangle Delta -Z Deltalab N = CZ r N = H o *NOTE: TEST # -OCTOBER 14, 2010, STUDENT I.D., CALCULATOR, PENCIL, ERASRERS. Qsos’s:  ~1963: Moarten Schmidt realized that we were looking at EXTEMELY red-shifted Hydrogen lines = large Triangle Delta.  Because V Triangle Delta, the radial velocity of Quasars is large. r  Because V d,rthe distance to the Quasars is great.  Hydrogen Spectrum in Lab compared to 3C273. LAB ^TWO BLUES ^434 ^ONE GREEN ^ONE RED. QSO ^503  What is the radial velocity of 3C273?  V =rC Triangle Delta Deltalab  Let Triangle Delta = Z such that Deltalab  V =rCZ = Z is called the “(red-shifted)”  V =rC (503-434) nm/434 nm  V =rC (0.16) = 0.16 C  = 16% of the speed of light!  V = 0.16 (3 x 10 ) m/s r 7 4  4.8 x 10 m/s = 4.8 x 10 km/s. 1000  *NOTE: Divide by 1000 to convert form from m/s to km/s.  Similarly, 3C48 was moving at 0.33C = 33% of the speed of light!  Hundreds of quasars are now known and ALL are EXTREMELY red-shifted.  What is the distance to 3C273?  *NOTE: Question on TEST # 1!  d = V r H o 4  d = 4.8 x 10 km/s 75 km/s/Mpc  d = 640 Mpc  d = (640 x 10 pc) (3.26 ly) = 2.09 x 10 ly 1 pc  d ~ 2 billion light-years distant. Relativistic Velocity Equation:  The fattest, most distant Quasar known has Z = 10.  Consider a Quasar with Z = 4.11.  Since V =rCZ, is this Quasar moving at 4.11 times the speed of light?  NO! No material object can exceed the speed of light.  For Z > ~ 0.5, we must turn to Relativity.  V =r[(Z + 1) – 1] C 2 [(Z + 1) + 1] Relativistic Velocity Calculation:  V =r[(4.11 + 1) – 1] C  V =r25.11 C 27.11  V =r0.93C = 93% of the speed of light! Distance to the Quasar:  If Hubble Law is valid, this Quasar must be VERY far away.  d = V H o 5  d = 0.93 (3 x 10 km/s) 75 km/s Mpc  d = 3720 Mpc = 12 x 10 ly9  d = 12 billion light-years distant!  To see Quasars over such vast (“Cosmological”) distances, they must intrinsically be VERY BRIGHT!  Quasars often emit as much energy as 100 to 1000 normal galaxies combined.  How big are they? What are they?  The size may be determined by a technique known as  LUNAR OCCULTATION.  *NOTE: SUN = SOL; MOON = LUNAR.  Moon “Beside” Quasar: Moon Occults Quasar:  Oo-Quasar Oo-Quasar  Apparent size of Quasar =
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