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 Cluster Simulation – Rotation Velocities 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