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Gravitational Lensing: How to See the Dark. J. E. Bjorkman University of Toledo Department of Physics & Astronomy. The Dark Between the Light. Dark Matter. How do we know its there? Answer: It affects the motion of everything we can see. Cluster Simulation Rotation Velocities.

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gravitational lensing how to see the dark

Gravitational Lensing: How to See the Dark

J. E. BjorkmanUniversity of Toledo

Department of Physics & Astronomy

dark matter
Dark Matter
  • How do we know its there?
  • Answer: It affects the motion of everything we can see.
    • Cluster Simulation
    • Rotation Velocities
what is the dark
What is the Dark?
  • MACHOs (Massive Compact Halo Objects)
    • low mass stars - "brown dwarves"
    • "almost" stars (planets, e.g. Jupiters)
    • black holes of less than solar mass
    • The VW graveyard
  • WIMPs (Weakly Interacting Massive Particles)
    • heavy neutrinos (10 to 1000 GeV)
    • new particles predicted by Supersymmetry - \'neutralinos\'
    • exotic particles – e.g. axions (particles with mass < 0.1 eV)
  • Modified Gravity - on galactic scales.
eclipse astrometry
Eclipse Astrometry
  • How do we know the stars moved?
measuring the dark
Measuring the Dark
  • 0.5% of Universe is luminous
  • 99.5% of Universe is dark matter
gravitational microlenses
Gravitational Microlenses
  • What are microlenses?
    • Stellar mass (or smaller) lenses
    • Images are unresovled (milliarcsecond separation)
    • Lens focuses light
    • Object appears brighter (several magnitudes!)
  • That’s absurd!
    • You’ll never see one in a million years!
  • Answer – just look at million stars every night!
microlensing searches
Microlensing Searches
  • Toward the Magellanic Clouds
    • MACHO (MAssive CompactHalo Objects collaboration)
    • EROS (Experience pour la Recherche d\'Objets sombres)
    • DUO (Disk Unseen Objects)
  • Toward the Galactic Bulge
    • OGLE (Optical Gravitational Lensing Experiment)
  • Toward M31:
    • AGAPE (Andromeda Galaxy Amplified Pixel Experiment)
    • MEGA
follow up monitoring
Follow-Up Monitoring
  • PLANET (Probing Lensing Anomalies NETwork)
  • Garching Spectroscopic Monitoring Group
  • GMAN (Global Microlensing Alert Network)
  • MPS (Microlensing Planet Search Project)
  • MOA (Microlensing Observations in Astrophysics)
micolensing results
Micolensing Results
  • They Exist! Future surveys will detect 1/day
  • Fewer than expected toward LMC/SMC
    • 50% of halo may be Machos (M = 0.5Msun)
  • More than expected toward Galactic center
    • Masses are few 0.1 Msun
    • May indicate presence of bar (i.e., Milky Way is a barred spiral)
  • About 10% are binary events
  • Planets
    • No definite detections, yet
    • Fewer that 1/3 of lenses have Jupiter-mass planets at 1-4 AU
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