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Gravitational Lensing.pptx
- 2. INTRODUCTION Einstein’s General theory of relativity Gravitation is only a superficial force Method of measuring space and time using properties of Euclidian geometry Reality Space time continuum in gravitational field of body Non Euclidian law of geometry or curved geometry
- 4. GRAVITATIONAL LENSING An astrophysical phenomena in which the distribution of mass in the universe affects the propagation of light. Works in an similar way to the description of the propagation of light through normal lenses Photon travels across the universe Gravitational effect of mass concentration Trajectories arepurturbed Refocuses somewhere else
- 6. GRAVITATIONAL LENSING Opticallensing • light bends due to refraction at spherical end and focuses into the eyes. Gravitationallensing • light bends around a concentration of mass (usually galaxies, stars, black holes) and refocuses somewhere else.
- 7. When contemplating near incredibly dense masses, the impacts can be exceedingly odd and very intense. As the light from lensed galaxies and clusters approaches the foreground cluster, it is stretched into arcs.
- 10. 1804 • “On The Deflection Of Light Ray From Its Straight MotionDueToThe Attraction Of A World Body Which It Passes Closely," • byJohannSoldner • Predictedthat a light ray passing close to the solar limb would be deflected by an angleα= 0:84arcsec. 1911 • Albert Einsteindirectly addressedthe influence of gravity on light 1913 • Einsteincontacted the director of Mount Wilson observatory, George Hale, and asked if it will be possible to measure the positions of stars near the sun during the day in order to establish the angular deflection effect of the sun
- 11. 1914 1916 • the completion of the General Theory of Relativity byEinstein • derivethe first correct formula for the deflection angleαof a light. • obtained deflection angle for sun asα= 1.74arcsec 1919 • . • Einstein foundα= 0.83arcsecfor the deflection angle of a light ray grazing the sun •The first observational attempt to test Einstein's prediction for the deflection angle •never accomplished •predicted value for the angular deflection was actually wrong.
- 12. 1924 • Chwolsonmentioned the idea of a“factious double star." • also mentioned the symmetric case of star exactly behind star, resulting in a circular image. 1936 • Einsteinalso reported about the appearance of a “luminous" circle of perfect alignment between the source and the lens, such a configuration is called“Einstein Ring". 1937 • Fritz Zwickypointed out that galaxies are more likely to be gravitationally lensed than a star and that one can use the gravitational lensas natural telescope.
- 14. PHENOMENA When a light ray follows the curvature, it bends towards the mass, causing space-time to curve. This bending gives rise to several important phenomena 1. Einstein rings 2. Giant luminous arcs 3. Multiply imaged quasars
- 15. EINSTEIN RINGS Special case of Gravitational lensing in which the source lies exactly behind the lens, a ring like image will be produced, called as Einstein rings.
- 17. Einstein Rings conditions to be satisfied in order to be able to observe Einstein rings the source must lie exactly on top of the resulting degenerate point-like caustic. the source must lie exactly on top of theresulting degenerate point-like caustic.
- 18. EINSTEIN RINGS Their diameters vary between 0.33 to 2 arcseconds They're all found in the radio frequency range, with several having vissible or infrared counterparts as well Some of them are "broken" rings having one or two interruptions along the circle The compact component is changeable and usually viewed as a double image divided by the it's diameter. The changeability of conpact source helps in measuring time delay and hubble constant in these systems.
- 19. EINSTEIN RING preliminary pictures of the gravitational lensing effect seen with a wine glass! Below is an image of a classic ‘Einstein ring’ that occurs due to extreme strong lensing effects. This is rarely seen in nature.
- 20. THE FIRST EINSTEIN RING The extended radio source MG1131+0456 Observed in 1988 discovered by Hewitt Diameter of about 1.75 arcsecond
- 21. GIANT LUMINOUS ARC magnified, distorted and strongly elongated images of background galaxies which happened to lie behind foreground clusters of galaxies.
- 22. GIANT LUMINOUS ARC • Clusters of galaxies with masses of order 10^14Mo are very effective lenses • TheirEinstein radii are of the order of 20 arcseconds • Giant arcs can be exploited in two ways : 1. they provide us with strongly magnified galaxies at (very) high redshifts. 2. as tools to study the potential and mass distribution of the lensing galaxy cluster
- 23. GIANT LUMINOUS ARC • An interesting result from the analysis of giant arcs in galaxy clusters is that Clusters of galaxies are dominated by dark matter • The fact that we see such arcs shows that the central surface mass density in clusters must be high. • core radii of clusters - the radii at which the mass profile of the cluster flattens towards the center-must be of order of this distance or smaller.
- 24. two of the most spectacular cluster lenses producing arcs: Clusters Abell 2218 CL0024+1654.
- 25. MULTIPLY-IMAGED QUASAR Multiply imaged quasar are effect of gravitational lensing. With a multiple imaged quasar, their light is lensed around an intervening galaxy before reaching Earth, producing multiple images of the quasar.
- 26. MULTIPY IMAGED QUASAR • the first example of a lensed object was a double quasar Q0957+561 • Quasars are rare and not easy to find-By now about two dozen multiply-imaged quasar systems have been found • The fraction of quasars that are lensed is small (less than one percent) • It is not trivial at all to identify the lensed (i.e. multiply-imaged) quasars among the known ones.
- 27. FIRST MULTIPLE IMAGED QUASAR •Discovered in 1979 •By Dennis Walsh •found in a radio survey
- 29. STRONG LENSING • occurs when source, lens and observer are well positioned and close enough, bending angle is large enough to resolve various images. • a lens with mass density higher than critical density is necessary • usually occurs in the central region of galaxies and clusters
- 30. STRONG LENSING • provide cosmological information 1. measurement of hubble constant 2. better understanding of evolution of structures in the universe • involves formation of multiple images and high magnification when source and observer is in proper alignment - rare event
- 31. FIRST STRONG LENSING •first strong lensing was seen in 1979 •by walsch carswell and waymann •doubly imaged Q0957+561 quasar
- 32. WEAK LENSING • small distortion in the patterns of background galaxies caused by the weak lensing of foreground galaxies • by statistical averaging of these small distortions we could estimate mass of cluster
- 33. Weak lensing
- 34. FIRST WEAK LENSING •first observed in 1990 •around the galaxy cluster of abell 1689 and CL409+524
- 35. MICROLENSING • type of gravitational lensing in which the gravitational lensing effect is small-scale • The lensing is of an image that is so small or faint that instead of observing multiple images, the additional light bent towards the observer making the source appears brighter. • The surface brightness remains constant but as numerous images of the object appear, the object appears brighter and bigger.
- 37. MACHOS(Massive compact halo object) Cant see directly but their gravitational lensing effects can be noticed when they pass in front of a source causes star to brighter for a while
- 39. • Gravitational lensing is an exceptional field in astronomy in the sense that its occurence and many of its features were predicted before they were actually observed. example: a. multiple images b. quasar microlensing c. galactic microlensing d. weak lensing
- 40. APPLICATIONS • gravitational lensing is a simple geometrical concept which easily allows 1. qualitative estimates and quantitative calculations 2. to look forward in time and predict future applications • Gravitational lensing is one of three methods used for the determination of masses of galaxy clusters Other two are: I. by X-ray analysis II. by using the virial theorem and the velocity distribution of the galaxies
- 41. MULTIPY-IMAGED QUASAR • more determinations of accurate time delays in quasar systems. • the value of the Hubble constant determined will be accurate than values obtained with any other method
- 42. QUASAR MICROLENSING EVENT • provide information on the structure of the quasars and the intervening clumped matter. • Maybe we can “map” the hot spots of quasars this way
- 43. GALACTIC MICROLENSING EVENT • to study the structure of the Milky Way • The spectra of highly magnified stars will help to investigate the metallicity of bulge stars in detail. • resolve the stellar surfaces and study their center-to-limb variations. • provide unbiased statistics on the fraction of binary stars (within certain relative distances).
- 44. GALACTIC MICROLENSING EVENT • has the advantage compared to all other Earth-bound planet search techniques that it is able to detect Earth-mass planets! • could be detected directly by monitoring astrometrically the position of the star very accurately • provide information on the three-dimensional mass distribution of the halo
- 45. WEAK LENSING EVENT • will be used to map not just the outskirts of massive galaxy clusters • to trace the large scale structure by its effect on the background population of galaxies. • we can ultimately produce a three-dimensional map of the matter in the universe (rather than a light map)! • useful thing for the understanding of structure formation and evolution • we will determine the matter content of the universe
- 46. OTHER POSSIBLE APPLICATIONS • a complementary determination of the black hole mass. • help to study the dynamics near the black hole. • detect the gravitational lens signature of the matter - the next generation of experiments to map the cosmic microwave background. • The redshift of the most distant object will be magnified.
- 47. • Ultimately every object in the sky is affected by (ever so slight) lensing effects Lensingoutlook at symposium 173 • “gravitational lens effects ... are present along virtually every line of sight” • more and more astronomers will (have to) deal withlensingin the next decade, so thatlensingwill become an “ubiquitous observational technique” and hence – for better or for worse: “gravitationallensingmay well disappear as a unique sub- specialty in astronomy”. CONCLUSION