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

Galactic Rotation Curves

Missing Mass in our Galaxy

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?

Gravity Bends Light (Einstien)

Gravitational Lenses

Einstein tells Eddington gravity bends starlight.

Eclipse Astrometry  How do we know the stars moved?

Relativity Verified

Discovery of a Gravitational Lens

Galaxies as Lenses

A Lensing Simulation

A Lens Gallery

Galaxy Clusters as Lenses

Measuring the Dark  0.5% of Universe is luminous  99.5% of Universe is dark matter

“Stellar Lenses” Orion behind a Black Hole

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  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

AGAPE at M31

Looking Through a Lens

A Lens in Motion

What You Really See

Looking for Lenses in Haystacks

Frequency of Events

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

What are They?

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

Binary Stars as Lenses

Looking for Planets

The Planet Search

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