Gravitational Lensing: How to See the Dark

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Gravitational Lensing How to See the Dark

• J. E. BjorkmanUniversity of Toledo
• Department of Physics Astronomy

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The Dark Between the Light
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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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Galactic Rotation Curves
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Missing Mass in our Galaxy
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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 lt 0.1 eV)
• Modified Gravity - on galactic scales.

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Where is the Dark?
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Gravity Bends Light (Einstien)
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Gravitational Lenses
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Einstein tells Eddington gravity bends starlight.
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Eclipse Astrometry

• How do we know the stars moved?

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Relativity Verified
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Discovery of a Gravitational Lens
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Galaxies as Lenses
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A Lensing Simulation
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A Lens Gallery
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Galaxy Clusters as Lenses
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Measuring the Dark

• 0.5 of Universe is luminous
• 99.5 of Universe is dark matter

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Stellar LensesOrion behind a Black Hole
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Gravitational Microlenses

• What are microlenses?
• Stellar mass (or smaller) lenses
• Images are unresovled (milliarcsecond separation)
  
• Lens focuses light
• Object appears brighter (several magnitudes!)
• Thats absurd!
• Youll never see one in a million years!
• Answer just look at million stars every night!

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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

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Ogling the Stars
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AGAPE at M31
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Looking Through a Lens
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A Lens in Motion
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What You Really See
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Looking for Lenses in Haystacks
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Frequency of Events
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How Big is the Lens? How Close did it get?
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What are They?
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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)

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Looking Through BifocalsBinary Stars as Lenses
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Binary Stars as Lenses
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Looking for Planets
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The Planet Search
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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