1. Gravitational Lensing Boot Camp Robert Nemiroff Michigan Tech

2. Abstract What is gravitational lensing, what has it told us about the universe, and what more can it tell us about the universe? Lenses such as black holes, stars, galaxies, clusters of galaxies, and the universe as a whole will be covered. Concepts such as Einstein rings, photon spheres, image pair creation events, and shear will be defined and briefly discussed. The intersection of gravitational lensing with current research frontiers will be reviewed including how microlensing is being used to search for extra-solar planets, how radio telescopes are being used to probe galaxy-center black holes, and how weak lensing is being used to probe galaxy evolution in the early universe. Possible lensing signals in continuing and upcoming missions such as Planck, DES, LSST, Euclid, and WFIRST will be reviewed. Relevant parts of the lecturer's own research will also be briefly mentioned.

3. Lensing: Suggested readings Wikipedia ◦ http://en.wikipedia.org/wiki/Gravitational_lensing Short ◦ http://astro.berkeley.edu/~jcohn/lens.html Medium ◦ Visual distortions near a neutron star and black hole, R. J. Nemiroff, 1993 ◦ http://adsabs.harvard.edu/abs/1993AmJPh..61..619N ◦ Movies: http://apod.nasa.gov/htmltest/rjn_bht.html Long ◦ Microlensing Surveys for Exoplanets, Gaudi, S. 2012 ◦ http://adsabs.harvard.edu/abs/2012ARA%26A..50..411G

4. Know Your Lecturer (highlights) Prediction & analysis of basic microlensing phenomena ◦ Nemiroff, 1987, Ph D., U. Penn. AGN broad emission line amplification from microlensing ◦ Nemiroff, 1988, Astrophys. J, 335, 593 Visual distortions near a neutron star and black hole ◦ Nemiroff, 1993, Am. J. Phys., 61, 619 Finite sources & the information content of microlensing ◦ Nemiroff & Wickramasinghe 1994, Astrophys. J., 424, L21 Gravitational Lensing Characteristics of the Transparent Sun ◦ Patla & Nemiroff 2008, Astrophys. J. 285, 1297 Also papers on cluster arcs, GRB lensing searches,etc.

5. Aside: Intellectual Prestige scale Mathematicians Theoretical particle physicists Theoretical physicists Experimental physicists Observational astronomers Astronomical data analysts (like me!) Philosophers Science popularizes (sorry)

6. Lensing: History 1801: Soldner with Newtonian gravity 1911 & 1915: Einstein with relativistic theories 1912: Failed attempt to find solar lensing 1919: Eddington et al. detect solar lensing 1979: Walsh et al. detect galaxy lensing 1986: Lynds & Petrosian recognize cluster lensing 1993: MACHO, EROS, OGLE find stellar lensing GR might be wrong but GL is certainly correct!

7. Lensing: Outline Concepts ◦ Einstein rings, photon spheres, magnification, shear, image pair creation events Lenses ◦ Universe, clusters of galaxies, galaxies, stars, black holes Frontiers ◦ Extra-solar planets, galaxy center black holes, cosmic tomography

8. Lensing: Outline Concepts ◦ Einstein rings, photon spheres, magnification, shear, image pair creation events Lenses ◦ Universe, clusters of galaxies, galaxies, stars, black holes Frontiers ◦ Extra-solar planets, galaxy center black holes, cosmic tomography

9. Concepts Einstein Ring ◦ Observed ring when point source is directly behind a point lens Photon sphere ◦ Distance from black hole where photons orbit in circles (unstable) Magnification ◦ Images become brighter or dimmer Shear ◦ Tangential stretching Image pair creation event ◦ And other light curve features

10. Credit: NASA, Wikipedia: Gravitational Lens Concept: Einstein Ring

11. Nemiroff, R. J. 1993, AmJPhys Orbiting near a black hole Concept: Photon SphereConcept: Einstein Ring

12. Nemiroff, R. J. 1993, AmJPhys

13. Wambsganss, 1998, Living Reviews Single star light curves Concept: Magnification

14. Nemiroff, Ph D. thesis, 1987 Double star light curves Concept: Image pair creation events

15. Concept: Image pair creation event Concept: Shear Time Delay Surface ERU = Einstein Ring Unit Nemiroff, R. 1988, Astrophys. Space Sci

16. Terminology: Strong vs. Weak Strong lensing ◦ Multiple images, large deflections ◦ Microlensing, galaxy lensing, femtolensing, etc. ◦ Galaxy halo probe, exoplanets, dark matter Weak lensing ◦ Single displaced images, small deflections ◦ Galaxies, distortions and tests of cosmology

17. Lensing: Outline Concepts ◦ Einstein rings, photon spheres, magnification, shear, image pair creation events Lenses ◦ Universe, clusters of galaxies, galaxies, stars, black holes Frontiers ◦ Extra-solar planets, galaxy center black holes, cosmic tomography

18. Lensing: Outline Concepts ◦ Einstein rings, photon spheres, magnification, shear, image pair creation events Lenses ◦ Universe, clusters of galaxies, galaxies, stars, black holes Frontiers ◦ Extra-solar planets, galaxy center black holes, cosmic tomography

19. Lens: Universe Standard Rulers ◦ Angular size changes can be strange ◦ Galaxies radius ◦ Baryon Acoustic Oscillations Standard Candles ◦ Dimming with distance depends on cosmology ◦ Perfect candles still have lensing dispersion Universe is not WYSIWYG! ◦ WYSIWIG=What You See Is What You Get  (A computer term)

20. Strani & Strabinski, 2000, Mod. Phys. D., 9, 373-443 Lens: Universe

21. Lens: Cluster of galaxies Dark matter fraction constraints ◦ Positions of arcs ◦ Smoothness arcs Not predicted because central density thought smaller Seen before it was noticed!

22. Lens: Cluster of Galaxies: Abell 2218 Credit: Andrew Fruchter (STScI) et al., WFPC2, HST, NASA Digitally reprocessed: Al Kelly

23. Lens: Galaxy Source: Quasars ◦ Mass distribution of galaxies ◦ Time delay between images and Hubble’s constant Source: Background galaxies ◦ 2D lens mass ◦ 3D universe mass distribution

24. The Einstein Cross Gravitational Lens Image Credit & Copyright: J. Rhoads (Arizona State U.) et al., WIYN, AURA, NOAO, NSF Lens: Galaxy

25. Image Credit: ESA/Hubble & NASA Lens: Galaxy: LRG 3-757

26. Lens: Star Source star light curves only ◦ Not resolved angularly

27. Lens: Black Hole Strong lensing ◦ Very high deflection angles ◦ Many images ◦ Complete image sets No confirmed BH lenses

28. Nemiroff, R. J. 1993, AmJPhys Orbiting at the photon sphere Lens: Black Hole

29. Lensing: Outline Concepts ◦ Einstein rings, photon spheres, magnification, shear, image pair creation events Lenses ◦ Universe, clusters of galaxies, galaxies, stars, black holes Frontiers ◦ Extra-solar planets, galaxy center black holes, cosmic tomography

30. Lensing: Outline Concepts ◦ Einstein rings, photon spheres, magnification, shear, image pair creation events Lenses ◦ Universe, clusters of galaxies, galaxies, stars, black holes Frontiers ◦ Extra-solar planets, galaxy center black holes, cosmic tomography

31. Frontier: Extra-solar planets (Microlensing) Gaudi, S. 2012, Ann. Rev. Astron. Astrophy.

32. Frontier: Galaxy Center Black Holes Very Long Baseline Interferometry ◦ Radio Interferometry ◦ Event Horizon Telescope (preliminary obs. ongoing) ◦ Photon sphere “shadow” on bright material behind Sgr A* and M87’s center ◦ Localizing Sgr A* with VLBI, Borderick, Loeb, & Reid, ApJ (2011) Very Large Telescope (ESO) ◦ Infrared Interferometry ◦ GRAVITY – 10 microarcsec astrometry (2014) ◦ Star deviations from Sgr A* lensing ◦ Observing Gravitational Lensing Effects by Sgr A* with GRAVITY, Bozza & Mancini, ApJ (2012)

33. Frontier: Cosmic Tomography (Weak Lensing)

34. Determine mass “power spectrum” ◦ Clusters of galaxies ◦ As matter clumps during universe evolution Ground ◦ Pan-STARRS (ongoing) ◦ Dark Energy Survey (ongoing) ◦ LSST (2014) Space ◦ Planck (2013) ◦ WFIRST (2023)

35. Lensing: My research Predictions ◦ Probability & Detection Volumes ◦ Microlensing of AGN ◦ Microlensing of stars ◦ Dark matter searches for millilensing in GRBs Strong effects near a black hole ◦ Neutron star

36. Nemiroff et al. 2001, Phys. Rev. Lett Searching the universe for million solar mass lenses

37. Surprise: Philosophy slide! There are only three numbers in science Zero (0) ◦ “It is too small to measure.” ◦ Example: electron radius One (1) ◦ “We measured it – and normalized it.” ◦ Example: Sun-Earth distance Infinity ( ∞ ) ◦ “It is too large to measure.” ◦ Example: complete universe radius