Gravitational lensing how to see the dark
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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

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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


The dark between the light

The Dark Between the Light


Dark matter

Dark Matter

  • How do we know its there?

  • Answer: It affects the motion of everything we can see.

    • Cluster Simulation

    • Rotation Velocities


Galactic rotation curves

Galactic Rotation Curves


Missing mass in our galaxy

Missing Mass in our Galaxy


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.


Where is the dark

Where is the Dark?


Gravity bends light einstien

Gravity Bends Light (Einstien)


Gravitational lenses

Gravitational Lenses


Gravitational lensing how to see the dark

Einstein tells Eddington gravity bends starlight.


Eclipse astrometry

Eclipse Astrometry

  • How do we know the stars moved?


Relativity verified

Relativity Verified


Discovery of a gravitational lens

Discovery of a Gravitational Lens


Galaxies as lenses

Galaxies as Lenses


A lensing simulation

A Lensing Simulation


A lens gallery

A Lens Gallery


Galaxy clusters as lenses

Galaxy Clusters as Lenses


Measuring the dark

Measuring the Dark

  • 0.5% of Universe is luminous

  • 99.5% of Universe is dark matter


Stellar lenses orion behind a black hole

“Stellar Lenses”Orion behind a Black Hole


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


Ogling the stars

Ogling the Stars


Agape at m31

AGAPE at M31


Looking through a lens

Looking Through a Lens


A lens in motion

A Lens in Motion


What you really see

What You Really See


Looking for lenses in haystacks

Looking for Lenses in Haystacks


Frequency of events

Frequency of Events


How big is the lens how close did it get

How Big is the Lens? How Close did it get?


What are they

What are They?


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)


Looking through bifocals binary stars as lenses

Looking Through BifocalsBinary Stars as Lenses


Binary stars as lenses

Binary Stars as Lenses


Looking for planets

Looking for Planets


The planet search

The Planet Search


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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