Gravitational Lensing: Gravitational Lensing: How to See the DarkHow to See the Dark

J. E. BjorkmanUniversity of Toledo

Department of Physics & Astronomy

The Dark Between the LightThe Dark Between the Light

Dark MatterDark Matter

How do we know its there?Answer: It affects the motion of everything

we can see.– Cluster Simulation– Rotation Velocities

Galactic Rotation CurvesGalactic Rotation Curves

Missing Mass in our GalaxyMissing 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 LensesGravitational Lenses

Einstein tells Eddington gravity bends starlight.

Eclipse AstrometryEclipse AstrometryHow do we know the stars moved?

Relativity VerifiedRelativity Verified

Discovery of a Gravitational LensDiscovery of a Gravitational Lens

Galaxies as LensesGalaxies as Lenses

A Lensing SimulationA Lensing Simulation

A Lens GalleryA Lens Gallery

Galaxy Clusters as LensesGalaxy Clusters as Lenses

Measuring the DarkMeasuring the Dark

0.5% of Universe is luminous

99.5% of Universe is dark matter

““Stellar Lenses”Stellar Lenses”Orion behind a Black HoleOrion behind a Black Hole

Gravitational MicrolensesGravitational 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 SearchesMicrolensing 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 Ogling the StarsStars

AGAPE at M31AGAPE at M31

Looking Through a LensLooking Through a Lens

A Lens in MotionA Lens in Motion

What You Really SeeWhat You Really See

Looking for Lenses in HaystacksLooking for Lenses in Haystacks

Frequency of EventsFrequency of Events

How Big is the How Big is the Lens? Lens?

How Close did it How Close did it get?get?

What are They?What are They?

Follow-Up MonitoringFollow-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 BifocalsLooking Through BifocalsBinary Stars as LensesBinary Stars as Lenses

Binary Stars as LensesBinary Stars as Lenses

Looking for PlanetsLooking for Planets

The Planet SearchThe Planet Search

Micolensing ResultsMicolensing 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