lecture21--29mar11

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					                Astro:
ASTR 1040 Accel Astro: Stars & Galaxies
                                                                       Tour of Galaxies
                                                          • Role of dust in absorbing/scattering light
                                                          • How can we map the spiral arm structure of our
                                                            Milky Way galaxy?
                                                          • Next turn to mysterious galactic center in Milky
                                                            Way: supermassive black hole
                                                          • Hubble using Cepheids showed Andromeda is a
                                                                             universe”
                                                            distinct “island universe” – another Galaxy !
                                                          • Read 20.1 Galaxy Types, and for Thurs lecture
                                                            20.2 Measuring Cosmic Distances and 20.3
        Prof. Juri Toomre TA: Nicholas Nelson               Hubble’
                                                            Hubble’s Law
        Lecture 21 Tues 29 Mar 2011
          zeus.colorado.edu/astr1040-
          zeus.colorado.edu/astr1040-toomre




                 Today                                               Crib Sheet Awards
 • New Homework Set # 9 passed out: Hubble Law
   + Distances HW # 8.5 due in class                                 Psychic Powers Award
 • Observatory Night # 6 tonight (Tues March 29)                           Stacey Rugenski
   8:30pm+ (signup)

                                                                 International Collaboration Award
                                                                           Tyler Blankenship




                                                          REMINDER
Review:
                                                                           Stars
One-
One-page story
                         o
                                                          Inventory of
                                                Edge-
                                                Edge-on
Cartoon sketch                                             stuff”
                                                          “stuff” making
of Milky Way                                              up our galaxy

                                                                            Gas


                     o
                                                 Top
                                                           + “dark          Dust
                                                             matter”
                                                             matter”




                                                                                                               1
                                                                                        associations”
                                                     Trifid emission nebula “O & B star associations”
                                                                 visible           Spitzer infrared
O & B star
associations


many cluster stars
join to blow
      bubbles”
“big bubbles”




                                  metals”
       Clicker – stars and “heavy metals”
 • The ages of stars suggest that the bulge
                                                    • B.    Disk stars are
                                                      continually forming out of
   and halo of the Milky Way formed before            gas that is more and
                                                            polluted”
                                                      more “polluted” by heavy
   many of the stars in the disk. Which would         metals.
   you expect to have more heavy metals
           metallicity)?
   (higher metallicity)?                            • The OLD globular
                                                      clusters in the halo were
                                  B.                  formed a long time ago
                                                      before the galaxy was so
 • A. Halo and bulge stars                            polluted – they have very
                                                           metallicities”
                                                      low “metallicities”
 • B. Disk stars
 • C. No difference




                                                                SEMI-
                                                                SEMI-WARM stuff: dust
ISM:
                                       “Reddens”
                                        Reddens”    • DUST: absorbs
A little DUST                           the light     visible and UV light
goes a long
way!                                                • Transparent to
                                                      long wavelengths
                                                      (red, IR, radio)
                                        Absorbs
                                        the light
                                                    • Emits IR light

                                                                                             Horsehead Nebula




                                                                                                                2
           Dust+dark
           molecular
           clouds

           Horsehead
              close-
           in close-up

           VLT


                          Eagle
                          Nebula




 Clouds + dust
in Eagle Nebula




                                                       Rosetta
                                                       Nebula
                                                       O & B star
                                                       carving +
                                                       dust filaments




                         Dark and dusty stellar nurseries




             Widefield
             Infrared
             Survey
             Explorer                                   Nebula
             (WISE)                                     RCW 49
                                                        Stellar jewels
                                                        Spitzer IR
             NGC 3603




                                                                         3
                                                          WHERE are we in MW?

                                                          Dust makes it hard to
                                                          estimate distances
                                                          (stars dimmed)
                        Complex cycle                                                Globular clusters on
                        is ongoing ….                                                COBE IR sky image


                                                                  SUN               Shapley’s (1920)
                                                                                    Shapley’
                                        Disk is busy!                         X     distances to
                                        Cycle of                                    globular clusters:
                                     The Star-Gas-                                  Sun at 18 kpc from
                                       stars gas
                                     Star Cycle                                     center (twice too far!)
                                         stars




                                                                  COLD stuff: dark clouds
             Clicker – galaxy center
                                                          • Molecular CLOUDS
  • We want to map out the structure of the
    central core of the Milky Way. What                   • Dark, dusty, cold                     CO
    wavelength should we be using, and why?                          K)
                                                            (10 - 30 K)                           Doppler
                                                                                                  Images
                                                          • Emit molecular
  • A. IR or radio                                          emission lines in far
                                            A.              IR, radio
  • B. visible light                                      • Orion image here in
                                                            carbon monoxide
  • C. X-rays                                               (CO) -- colors are
                                                            Doppler shifts




          COLD hydrogen throughout
• Even the coldest                                        Q: Just HOW do we
                                                          know that MW has
  hydrogen emits
                                                          spiral structure?
  faint emission line
  in the RADIO                                            A: Radio astronomers
                                                          could map it with
• Wavelength 21 cm                                        21-
                                                          21-cm line of hydrogen

• Emission from flip of
                            All sky 21 cm radio mapping
  electron from spinup to
  spindown state




                                                                                                              4
                                                          Green Bank 100 m Radio Telescope VA

 21 cm
 emission
 (radio)

Sampling
neutral hydrogen
atoms (cold)

also how MRI
does it in medical
imaging!




      VLBA Radio Telescope Owens Valley                     Very Large Array (VLA) Socorro NM




                             VLA - Sicorro




                                                    Another view
                                                    of 21 cm radio
Radio mapping
                                                    mapping
cool H clouds
in MW disk                                                        SUN o

                                                    Beam cuts across
            SUN o                                   different spiral arms




                        o         Doppler shifted
                                  radio emission




                                                                                                5
    Radio map (21 cm) of spiral structure in MW

                                   SUN
                                                   Close-
                                                   Close-up view
Ragged spiral                        x             of our vicinity
structure revealed



Emitted radio                                                                   o
                                     o
waves can
penetrate through                 GALAXY
                                  CENTER                                                             “Orion
gas and dust
                                                                                                      arm”
                                                                                                      arm”



                                                                               toward
                                                                            galactic center




                 Center of our galaxy
                                                  • Dust obscures our
                                                                                              MW center
                                                    vision of much of the                      39’
                                                                                               39’ box
                                                    galaxy in visible and
                                                    UV light.

                                                  • X-rays only highlight
                                                    the hottest and
                                                    weirdest places

                                                  • IR and radio light
                                                    pass through
                                                    unaffected, show
           Located in direction of Sagittarius      dust, stars, gas




                                                  Galactic center: IR reveals a dense star cluster

 Unusual activity
 at galaxy center




                                                                                              IR 1




                                                                                                              6
              Radio
              mapping       Radio 3
              of galactic
              center                                                  IR 5



                            Radio 4



                                Zooming in on
                                Sagittarius A*
                                                            Radio 2




                             Sgr A*       VLT in IR + adaptive optics
                             orbits


Sgr A*

VLT
IR+AO




                                                                 Sgr A*
Star motion
around
                                                                 orbits
black hole
at galactic
center

VLT: IR+AO




                                                                             7
Rotation velocity at galaxy center


                            Some of central mass
                            is stars, joined by
                                 +/-
                            3.7 +/- 0.2 million
                            solar mass
                            BLACK HOLE
                                   But further 20%
                                   uncertainty from
                                   distance determination



Black hole still less than 1/1000 of MW mass




                                                            8

				
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posted:7/14/2011
language:English
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