Special Lectures onExperimental Gravity
GRAVITATIONAL LENSING
Paul Lasky
Experimental Gravity -- Gravitational Lensing
Contents★ A history of Gravitational Lensing
★ On the contents of the Universe
★ Strong Lensing
★ Weak Lensing
★ Microlensing
Experimental Gravity -- Gravitational Lensing
A (very short) history ofGravitational Lensing
Experimental Gravity -- Gravitational Lensing
★ 1704 - Newton, Optiks: “Do not Bodies act upon Light at a distance, and by their action bend its rays; and is not this action strongest at the least distance?”
★ 1784 - Henry Cavendish calculates deflection angle of corpuscular light ray in Newtonian gravity
★ 1804 - von Soldner calculates deflection of 0.84 arcsecs for stars close to the limb of the sun. Value considered too small to be observationally relevant.
★ 1800’s - Corpuscular theory of light is disfavoured for wave theory. General confusion over whether deflection is expected for a light wave.
Lensing prior to Einstein
! = 2GM/Rc2Newton
Cavendish
Experimental Gravity -- Gravitational Lensing
★As early as 1912, Albert Einstein predicted that a geometric theory of gravity would exhibit this phenomena
★He begins to search for observers to verify his prediction:★ Erwin Findlay-Freundlich - a German national went to
Crimea in August 1914 to observe eclipse. War is declared and he is arrested!
★ William Wallace Campbell - a US citizen is free to leave Russia on an expedition in 1914, but his equipment is impounded! Inferior equipment at an eclipse in 1918 yields a null result. He does not publish.
★ 1915 - Einstein publishes theory of GR and predicts new value for deflection angleSolar deflection angle is calculated to be 1.75 arcsecs - double the Newtonian (corpuscle) value.
Lensing as a purely geometric effect
! = 4GM/Rc2
Einstein
Findlay-Freundlich
William Wallace
Experimental Gravity -- Gravitational Lensing
1919 Eclipse★ In 1919, (Sir) Arthur Eddington went to Island
of Principe, off west Africa to observe a total eclipse. Another team went to Sobral, Brazil.
★ 2 plates in Principe successful; measured
★One telescope in Sobral gave★Another gave
★Eddington only published the two values in agreeance with GR prediction
★First experimental verification of GR!!★Einstein becomes famous!!!!★ (The 2nd telescope from Sobral has since been heavily debated.
Possibly out of focus, possibly also gives good agreement with other plates!)
Principe
! = 0.93 arcsec! = 1.61± 0.30 arcsec
! = 1.90± 0.11 arcsecEinstein & Eddington
Experimental Gravity -- Gravitational Lensing
Pospieszalska-Surdej, A., Surdej, J., and Veron,
P., ``The `Gravitational Lensing'
Bibliography'', in Astrophysical
Applications of Gravitational Lensing: IAU
Symposium 173, 415-418, (Kluwer,
Dordrecht, 1996).!
Experimental Gravity -- Gravitational Lensing
Pospieszalska-Surdej, A., Surdej, J., and Veron,
P., ``The `Gravitational Lensing'
Bibliography'', in Astrophysical
Applications of Gravitational Lensing: IAU
Symposium 173, 415-418, (Kluwer,
Dordrecht, 1996).!
Press (1996): “This is easily done by the rigorous mathematical technique of linear extrapolation... One sees that by the year 2008, all astronomical work will be devoted to gravitational lenses; by the year 2046, gravitational lens work will take over all scientific research; and by the year 2100, all humans will be devoted to our field.”
Experimental Gravity -- Gravitational Lensing
★Coles 1999, Einstein and the total eclipse
★Crelinsten 2006, Einstein’s jury: The race to test relativity
★Stanley 2007, Practical mystic: Religion, Science and A. S. Eddingtion
★Gates 2009, Einstein’s telescope: The hunt for dark matter and dark energy in the Universe
Much Longer Histories of Lensing
Experimental Gravity -- Gravitational Lensing
A (very short) Cosmology Primer
Experimental Gravity -- Gravitational Lensing
Standard Cosmology Ingredients★General Relativity★Cosmological Constant★Homogeneity & isotropy assumptions (FRW
Universe)
“Precision” cosmological observations★Supernova (SN Ia) (Riess et al. 1998, Perlmutter et al.
1999 - both over 5000 citations - cosmological revolution!)
★Cosmic microwave background (WMAP1 - 2003, WMAP3 - 2007, WMAP5 - 2009, Plank)
★Baryon acoustic oscillations (SDSS)
★Gravitational lensing surveys (CASTLES, CLASS, etc.)
★Integrated Sachs-Wolfe effect (Cross-correlations)
★Rotation curves of galaxies
Experimental Gravity -- Gravitational Lensing
Combining the assumptions with the observations leads to...
The currently accepted “Standard model of Cosmology”
ΛCDM
Experimental Gravity -- Gravitational Lensing
Combining the assumptions with the observations leads to...
ΛCDMDark Energy Cold Dark Matter
★ Cosmological Constant?★ Dark fluid?★ ??????
★ Non-baryonic★ Weakly
Interacting Massive Particles (WIMPS)????
★ ?????
★ Stars, galaxies, clusters, you, me, ... ALL baryons!
Experimental Gravity -- Gravitational Lensing
Combining the assumptions with the observations leads to...
ΛCDMGravitational lensing is one of the KEY tools to
discovering more about cosmology:★dark matter★dark energy★the accelerating Universe★the law of gravity
PLUS other exciting astrophysical objects including:★Extra-solar planets★black holes★wormholes (?) ...
Experimental Gravity -- Gravitational Lensing
Simply... the deflection of light by mass
What is gravitational lensing?
Gravitational lensing allows us to:★ Study the object emitting the light that gets deflected -- the “source”
★ The source can be amplified allowing us to see objects we would not otherwise have been able to.
★ Study the object causing the deflection -- the “lens”★ Lensing traces mass, even if we can’t see the mass!
Gravitational lensing comes in 3.5 flavours:
Strong, Weak and Microlensing(flexion)
Experimental Gravity -- Gravitational Lensing
Strong Gravitational Lensing
Experimental Gravity -- Gravitational Lensing
Strong lensing - Multiple Images
Quasar (source)at z ~ 1.69
lens at z ~ 0.04
Quasar (source)at z ~ 1.41
lens at z ~ 0.36
Experimental Gravity -- Gravitational Lensing
Strong lensing - Arcs and Arclets
Experimental Gravity -- Gravitational Lensing
Strong lensing
Observer
Source
Experimental Gravity -- Gravitational Lensing
Strong lensingSource
Observer
Experimental Gravity -- Gravitational Lensing
Strong lensingSource
Observer
Image
Image
Multiple images with high magnification
Experimental Gravity -- Gravitational Lensing
Perfect alignment of lens and source ==> Einstein ring
Hubble has even detected adouble Einstein ring!
what could this be?
Experimental Gravity -- Gravitational Lensing
Dark Matter Maps
Position and sizes of arcs allows for the creation of dark matter maps of clusters
Experimental Gravity -- Gravitational Lensing
Testing theory of gravity?Abell 1689 - a straight lens
But MANY people don’t believe dark matter exists
Require a modification of gravity to achieve this!
Many such theories exist that modify gravity on various scales
Experimental Gravity -- Gravitational Lensing
Testing theory of gravity?Abell 1689 - a straight lens
Then how do we explain “straight” arcs??
Experimental Gravity -- Gravitational Lensing
Weak Gravitational Lensing
Experimental Gravity -- Gravitational Lensing
Weak Lensing - Small shape distortions
Experimental Gravity -- Gravitational Lensing
Observer
Source
Weak lensing
Experimental Gravity -- Gravitational Lensing
Weak lensing
Observer
Source
Shape changes with low magnification
Experimental Gravity -- Gravitational Lensing
Weak lensing Surveys (cosmic shear)★ Simulate entire Universe in a computer (Nbody simulations)★ “ray-trace” path of photons through simulation★ Collect statistics on change of shape of images (shear)★ Compare with large
scale surveys which observe large numbers of distant galaxies
Experimental Gravity -- Gravitational Lensing
Back to ΛCDMMany free parameters, requires fitting by various observations
rms l
inea
r de
nsity
con
tras
t(C
lum
pine
ss o
f Uni
vers
e)
total matter density(dark matter + baryons)
Density perturbation spectral index(Measure of flatness at end of inflation)
Experimental Gravity -- Gravitational Lensing
Determining the nature and quantity of dark matter in the Galaxy and in Clusters of galaxies
Elliptical galaxies
Globular Clusters
UCDs
Forbes et al. 2008
(a small lie: virial mass here NOT measured using grav. lensing. But it could have been, and the principal is the same!)
Experimental Gravity -- Gravitational Lensing
Determining the nature and quantity of dark matter in the Galaxy and in Clusters of galaxies
Elliptical galaxies
Globular Clusters
UCDs
Forbes et al. 2008
(a small lie: virial mass here NOT measured using grav. lensing. But it could have been, and the principal is the same!)
Extend this plot much higher in masses by using weak lensing maps of clusters!
Experimental Gravity -- Gravitational Lensing
Testing theory of gravity?The Bullet Cluster
Contours - Mass inferred from weak lensing measurementsPretty colours - X-ray emission
Can this be explained without dark matter??
Experimental Gravity -- Gravitational Lensing
Microlensing
Experimental Gravity -- Gravitational Lensing
Strong lensingSource
Observer
Image
Image
Experimental Gravity -- Gravitational Lensing
Strong lensing+ Low mass lens
Observer
Experimental Gravity -- Gravitational Lensing
Strong lensing+ Low mass lens= Microlensing
Observer
★Can not resolve images★Magnification effects★Lens mass: 10-6 < M/M_sun < 106
Experimental Gravity -- Gravitational Lensing
Microlensing:Requires relative
motions
Observer
Magnification varies on scales of days to weeks
Source
Lens
Velocity orthogonal to line of sight
Experimental Gravity -- Gravitational Lensing
Microlensing - Light curves and magnification
Experimental Gravity -- Gravitational Lensing
Microlensing - Light curves and magnification
Experimental Gravity -- Gravitational Lensing
Extrasolar planets from microlensing
Large microlensing event changes magnification of source objectTiny perturbation reveals a low-mass planet!
time
Experimental Gravity -- Gravitational Lensing
Extrasolar planets from microlensing
Experimental Gravity -- Gravitational Lensing
Lots of things not covered!!!
★ Schneider, Ehlers & Falco (1992) Gravitational lenses, Springer ★ does not include recent developments, but very thorough introduction to theory of
lensing)
★ Bartelmann & Schneider (2001) Weak gravitational lensing, Physics Reports 340, 291
★ Wambsganss (1998 - updated in 2002) Gravitational lensing in astronomy, Living Reviews in Relativity
★www.livingreviews.org; emphasis on strong lensing
★ Ellis (2010) Gravitational lensing: A unique probe of dark matter and dark energy, Philosophical Transactions of the Royal Society A 368, 967
★Very nice review of recent developments associated with cosmological applications