sign in sign up
<<
Home , Elliptical galaxy

1

THE SEARCH FOR USING GRAVITATIONAL LENSING

RONALD E. MICKLE Denver, Colorado 80005 ©2008 Ronald E. Mickle

ABSTRACT Dark matter and dark energy comprise over 90% of the Universe. Dark matter has not been detected, cannot be seen and fails to emit electromagnetic radiation that we can detect. In the Universe, the ratio of the average density of matter and energy is the density parameter (Ω0) and is referenced in determining the fate of the Universe. Current observations based on WMAP, combined with Baryon Acoustic Oscillations and SNeIa indicate that ΩB = 0.0462 ± 0.0015, ΩD = 0.233 ± 0.013, and ΩΛ = 0.721 ± -1 -1 0.015, using H0 = 70.1 ± km s Mpc . These cosmological observations means the Universe is flat, with Ω0 = 1. The search for dark matter using gravitational lensing provides the backdrop to explanations to what dark matter is and why it is important. Among the myriad of particle candidates for dark matter, two stand out: the WIMP and the axion. Gravitational lensing as a tool can help determine the mass of and clusters, because lensing is an indicator of both the total mass of baryonic matter AND dark matter. While a large number of dark matter studies have been conducted using gravitational lensing, the methods continue to be improved. With the placement of new space based observatories, such as GLAST, astronomers and other scientist will continue to move closer to determining the composition of dark matter and the fate of the Universe.

1. INTRODUCTION necessary to keep the objects together. This missing mass is therefore referred Dark matter and dark energy are to as dark matter (Martin). believed to be most of what the Universe The search for dark matter using is composed of. Thus far, it has not been gravitational lensing provides the directly detected, cannot be seen and backdrop to explanations to what dark fails to emit electromagnetic radiation matter is and why it is important. The that we can detect. We believe dark nature of dark matter has intrigued matter exists because of the motions of astronomers and physicists for decades, , galaxies and galaxy clusters, but in much the same way black holes and there are alternatives such as Modified worm holes have fascinated the public Newtonian Dynamics, or MOND. By and science fiction writers. All these measuring the velocity of these mysteries are theorized and studied, but astronomical objects, we know that the cannot be physically observed. mass has to be sufficient to keep the Theoretical physics is rich with names of stars, galaxies or galaxy clusters from exotic elementary particles such as flying apart. In the case of large scale muons, bosons, leptons, up quarks, down velocity measurements, the amount of quarks and charm quarks. Of particular baryonic matter or luminous matter is interest in the search for dark matter is only a smaller portion of the total mass the neutrino. Dark matter could take on 2

other forms of ordinary non-luminous  If Ω0 < 1, the Universe is matter such as planets and stars that did open and will expand forever. not reach enough mass to start nuclear  However, if Ω0 = 1, then the reactions in their core, or dark remnants Universe is considered flat of collapsed giant stars similar to black and the expansion proceeds holes (Livio 2000). Livio (2000) adds forever with the expansion that observations have discounted most speed approaching zero. of these theories. According to Livio (2000) presents the analogy Kamionkowski and Koushiappas (2008) using the kinetic energy of the Universe among the myriad particle candidates for as either smaller or larger than the dark matter, two classes are most gravitational energy in determining the promising, the weakly interacting expansion rate. In determining the massive particle (WIMP) and the axion. calculation Ω0, it is important to note WIMPs consist of subatomic particles that (ρ) represents the total mass/energy which have mass and interact weakly in the Universe, including baryonic and with baryonic matter, while the axion is dark matter, as well as dark energy and a hypothetical lightweight particle with a is represented by their sums virtual infinite lifespan (Smoot & Ω0 = ΩB + ΩD + ΩΛ Davidson 1993). where ΩB is the density parameter for Dark matter is important because it baryonic matter, ΩD is the density helps explain the disparity in the galactic parameter of dark matter and ΩΛ is the rotational curves of stars in the outer density parameter for dark energy. regions of elliptical galaxies where stars Current observations based on WMAP exhibit velocities higher than would be combined with Baryon Acoustic expected, suggesting the presence of Oscillations and SNeIa indicate that ΩB dark matter in galaxies. On a much = 0.0462 ± 0.0015, ΩD = 0.233 ± 0.013, larger scale dark matter plays a and ΩΛ = 0.721 ± 0.015, using H0 = 70.1 considerable role in determining the fate ± km s-1 Mpc-1 (Hinshaw et al. 2008). of the Universe. The mean density of These cosmological observations mean matter in the Universe (ρ) is the total the Universe is flat, with Ω0 = 1. mass of the Universe divided by its Other evidence of dark matter is volume, and has been refined over the exhibited in galaxy clusters such as -27 -3 years to approximately 10 kg cm (see Figures 1 and 2) which (Sartori 1996). By comparison, the are surrounded by x-ray emitting gas in -20 -3 density of interstellar gas is 10 kg cm excess of a million degrees. The 17 -3 while a neutron is over 10 kg cm luminous components alone do not exert (Illingworth & Clark 2000). The ratio of enough gravitational influence to keep the average density of matter and energy the gas from evaporating; there is a large is the density parameter (Ω0) and given dark matter component distributed as Ω0 = ρ/ρc where ρc is the critical roughly in a spherical halo around the density and is referenced in determining cluster. Dark halos are commonly the fate of the Universe. inferred in discussions of invisible dark  If Ω0 > 1, the Universe’s matter that permeates galaxies and expansion will stop, start galaxy clusters. It is suggested that the contracting, leading to the big ’s dark halo extends beyond crunch. 3

92 kpc, well past luminous baryonic studies and others are founded on the matter. theory that dark matter is a form of The search for dark matter employs weakly interacting massive particles and various methods, one being finding may be detected directly in laboratory WIMPs through the use of scintillating experiments on Earth. This paper, crystals (Lang et al. 2008) and energetic however, focuses on attempts to detect neutrinos from WIMP annihilation rate dark matter through the use of in the (Kamionkowski & gravitational lensing. Koushiappas 2008). These particular

Figure 1: Abell 2029 (optical image) is Figure 2: Abell 2029 (x-ray image) a composed of thousands shows the cluster is embedded in an of galaxies. A large elliptical galaxy is enormous cloud of hot X-ray emitting at center surrounded by smaller gas. This hot gas would evaporate from galaxies. Distance: 1-Gly. Scale: 8x5 the cluster if a dark halo were not arcmin, cropped for publication. present. Scale: 8x5 arcmin, cropped Credit: NOAO/Kitt Peak/J.Uson, D.Dale, for publication. Credit: S.Boughn, J.Kuhn) NASA/CXC/IoA/S. Allen et al.

2. GRAVITATIONAL LENSING the Einstein rings or multiple images and is created by a smooth mass distribution Gravitational lensing is when a such as a galaxy or cluster of galaxies. massive referred to This is also referred to as macrolensing as the lens, aligns with the observer’s (Illingworth & Clark 2000). References line of sight and another object on the far appear to use the terms macrolensing side of the lens, referred to as the source, and strong lensing interchangeably as illustrated in Figure 3. When this (Falco et al. 1996; Safonova et al. 2001; happens, the light rays from the source Zakharov et al. 2004). Weak lensing is object are bent around the lensing object similar to previously described providing a distorted view of the source macrolensing, but on a smaller scale. which would normally not be visible Small magnifications result in small from behind the lens. shape changes and are independent of There are three general classes of source size or the lensing. Microlensing gravitational lensing: strong, weak and occurs when the lens mass is sufficiently micro lensing. Strong lensing exists small such that the multiple images are where there are visible distortions separated by microarcseconds and created by the lensing mass, such as arcs, 4

cannot be resolved, but can be detected While relativity predicted the as an increase in the source brightness. bending of star light close to the sun, the Visually, the source appears theory has applications for objects at elongated tangentially to the center of great distances. Gravitational lensing the lens. In galaxy clusters, blue arclets defers from optical lens in that it focuses may be seen, although weakly lensed parallel light from infinity to a line (Illingworth & Clark 2000). instead of a focal plane. Any observer Microlensing occurs when there is no on the opposite side of the lens from the distortion of the source star, only a source would see a focused image. photometric increase in brightness. This The first object gravitationally lensed increase in brightness happens when the was the double QSO 0957+561 lensing object, such as a brown dwarf or (Figure 4) in 1979 (Walsh et al. 1979; other massive object in the dark halo of Weymann et al. 1979). Initial viewing the Milky Way, passes in front of the shows what appear to be two objects, but source star. The amplification by the closer scrutiny reveals three. lensing is very rare and requires precise photometric measurements.

Figure 4: QSO 0957+561, B. Keel, Univ. of Figure 3. http://relativity.livingreviews.org/Articles/lrr- Alabama, Dept of Physics & . 1998-12/ HST/WFPC2

QSO 0957+561 is not in perfect lens. In this basic setup (Figure 3), a alignment with our line of sight, but is point-like lens will always result in at offset by approximately 6 arcsecs, with least two images, S1 and S2 . one image almost directly behind the In the Schwarzschild lens model, the lensing galaxy. Schwarzschild lens mass L in the lens plane is the lensing model is considered the simplest and object. The deflection angle for the most basic of setups for a point source S Schwarzchild lens is and lens L. The observer O views light emitted by the source deflected by the 5

referenced the stellar count toward determining the Milky Way’s galactic morphology and the recent press release by the Spitzer Science Center measuring where M (ξ) is the mass inside a radius stellar densities in determining the ξ (Wambsganss 1998), G the Galaxy had two major arms, rather than gravitational constant and c the speed of four (Clavin 2008). light. The closer the light ray passes to Gravitational lensing is supported by the lensing mass, the greater the General Relativity’s third prediction, a deflection. concept where a gravitational field bends If the point source S is directly in light. A mass exerting a strong line with the observer O and the gravitational field can further focus the Schwarzchild lens (L), the resultant light rays similar to a lens. The bending image is called the or of light postulated by Einstein can be Einstein radius, with radius explained by the principle of equivalence, using the accelerating elevator analogy to demonstrate. The hypothetical experiment demonstrates . the bending of light in a gravitational The distances D are angular diameter field when a beam of light enters the between O, L and S. elevator at right angles to its direction of travel. The elevator accelerates upward Astrophysicists know dark matter in its reference frame, but the light beam exists because of the causal factors it travels a parabolic path downward. The exhibits on other matter. Dark matter upward acceleration of the elevator is exerts gravitational forces on the equivalent to the gravitational field baryonic matter and can be mapped directed downward. (Sartori 1996) based on the gravitational lensing effect. Scientists were able to first test this Dark matter manifests itself is through hypothesis during the solar eclipse on the lumpiness in the cosmic microwave 1919 when astronomers measured the background and the motions of galaxies predicted deflection of starlight passing in galaxy clusters (Bally & Reipurth close to the limb of the sun. 2006), as well as the accelerated expansion rate of the Universe (Riess et 2.1. Importance of lensing as a tool al. 2004; Astier et al. 2006; Szydlowski in the Search for Dark Matter & Tambor 2008). The significance of dark matter can be found in the effects it Searches for dark matter within our has on cosmological objects. Studies own galactic or beyond the conducted during the early years of Milky Way, rely strongly on searches for dark matter using gravitational lensing as a tool for several gravitational lensing in the galactic halo, reasons. Accurate mass measurements lead some scientists to speculate that the of galaxies and clusters are necessary in Galaxy’s outer disk was distorted, order to develop strong constraints on warped and not the flat exponential disk estimates and models. Within galaxies we had grown accustomed believing and clusters, the mass function and (Evans et al. 1998). It is interesting to power spectrum can be attributed to dark note that the Evans et al. (1998) study 6 matter and dark energy, but the MACHOs have been suggested as dynamics are dominated by dark matter. possible candidates for dark matter. (Halkola et al. 2008) Using gravitational Both the Spitzer Space Telescope (SST), lensing as a tool, we can determine the launched in 2003 with its Infrared Array mass of galaxies and galaxy clusters, Camera (IRAC) and the Hubble Space because lensing is an indicator of both Telescope (HST) have been used by the the total mass of baryonic matter AND MACHO collaborators to search for dark matter. MACHOs in the dark halo surrounding The angle the light ray is bent is the Milky Way. Spitzer IRAC is determined by the point lens mass, particularly useful in searching for hence, the gravitational force exerted. brown dwarfs in the galactic halo due to Einstein’s theory of General Relativity their low surface temperature emitting in indicates that the energy of the the IR and near-IR part of the spectrum. gravitational field be determined by the The studies conducted by the matter distribution. Neither the MACHO collaborators focused on gravitational field nor the deflection photometry data most likely to contain angle depends on the type of matter; candidates for microlensing, which was therefore, matter density may be MACHO-LMC-5 and MACHO-LMC- baryonic matter, dark matter, or both. 20, hereafter referred to as Event-5 and (Bartelmann and Schneider 2001) Event-20. Event-5 was also recorded with HST. Great progress has been 3. LENSING-BASED SEARCHES FOR made toward the analysis and data DARK MATTER WITHIN THE MILKY reduction of gravitational microlensing WAY GALAXY AND THE KEY events since the first recorded detection RESULTS was published in Nature in 1993 (Nguyen et al. 2004). Since then, over The idea was first proposed in 1986 12 million stars from LMC have been to use microlensing to detect Massive analyzed (Minniti). Compact Halo Objects (MACHOs) in Spitzer IRAC was used to record the the galactic halo by monitoring stars in source star of Event-5, 10 years after the the Large and Small Magellanic Clouds initial imaging. In 1993, Macho (LMC and SMC). Objects in the halo of collaborators recorded a brightness the Milky Way, such as brown dwarfs or factor of 47 over 76 days. Around 2001, black holes can produce microlensing of HST WFPC2 was able to record both the a distant star, causing it to brighten. source and the lens. By 2004, the source These microlensing objects are referred and the lensing mass had separated by to as massive compact halo objects or ~0”.24, and again HST was used to MACHOs for short. If a MACHO came image the event, this time using into alignment with the observer and the ACS/HRC. The conclusion was the lens distant star, the brightness of the star mass was probably a dwarf M5 star at would increase through lensing. For ≈600 pc. Resolution of Spitzer is detection, millions of stars in the LMC reported as ~1”.8 at FWHM of the PSF. and SMC would have to be monitored. It is unknown if removal of instrumental (Livio 2000 p93) Until the nature of effects through deconvolution was dark matter is determined, scientists of undertaken. By removing the V-I color course cannot rule out baryonic matter as index through data reduction, the a possible dark matter candidate. Hence, 7

MACHO collaborators estimated the deviated by more than 3σ from its source contributed <10% of the neighbors (Evans & Belokurov 2005). combined flux of Event-5, showing a However, the study by Evans and substantial infrared excess. Therefore, Belokurov (2005) which used a neural MACHO-LMC-5 exhibited colors networking method, was also challenged corresponding to a late M dwarf or early as stating their analysis contained several L dwarf star of ~0.2 Mʘ. The errors and used 0.2% of the available collaborators felt that Spitzer’s MACHO dataset (Griest and Thomas capabilities in detecting cool, low mass 2005). There is room for humor in stellar lens had been well demonstrated. scientific debates as quoted by Evans (Nguyen et al. 2004) and Belokurov (2005) in their response The data reduction and analysis of to the challenge by Griest and Thomas the MACHO collaborators appears (2005), “Of course, there is no need to sound but their calculations of optical re-enact the epic battle between the mice depth  appear to be in conflict with and the frogs…in the pages of this other studies (Evans & Belokurov 2005). Journal.” Healthy academic In analyzing the photometry of the disagreement is, for science, a good source and the lensing mass, the flux is thing. Bennett et al. (2005) argues that computed using the distance. The Evans and Belokurov (2005) over amount the flux is reduced after confidence in the neural networking traveling through the medium is . An method may have led them to over optical depth of zero means the medium interpret the results. As described by is transparent, with the opacity Bennett et al. the black box nature of decreasing as the optical depth number neural networking is that decisions are increases. A larger  would be difficult to troubleshoot. Bennett et al. indicative of a greater amount of dark refined previously unpublished matter in the medium of the halo. photometry and combined microlensing (Illingworth & Clark 2000) A second light-curve fitting with photometry from collaborative team, EROS, also HST images, used difference image conducted searches for MACHOs within photometry of images captured with the the dark halo of the Milky Way and 1.3 m Skymapper at MSSSO (referenced concluded with the team of Evans and as the Great Melbourne telescope in their Belokurov (2005) that the computed study), and used follow up images from optical depths are much less than that of the 0.9 m CTIO telescope. Bennett et al. the MACHO team. Belokurov et al. (2005) published the comparison results stated they discarded data points that (Table 5) of Evans’ and Belokurov’s (2005) and MACHO in the following table.

8

TABLE 5 Event Classification Event MACHO Verdict BEL Verdict Confirmation Mancini et al. Lens Type 1 lens-A lens Clump giant Non-LMC 4 lens-A Variable CTIO+DIP phot. Non-LMC 5 lens-A lens Lens ID MW disk 6 lens-A lens-A --- LMC 7 lens-A Variable --- Non-LMC 8 lens-A Variable --- LMC 9 lens -B --- Caustic binary LMC 10 SN lens HST: galaxy --- 11 SN SN HST: galaxy --- 12 SN SN HST: galaxy --- 13 lens-A Variable CTIO+DIP phot LMC 14 lens-A lens CTIO+DIP phot LMC 15 lens-A Variable CTIO+DIP phot non-LMC 16 SN --- CTIO: galaxy --- 17 SN SN CTIO: galaxy --- 18 lens-A Variable --- non-LMC 19 SN SN CTIO: galaxy --- 20 lens-B SN ------21 lens-A lens --- non-LMC 22 B lens MSSSO: galaxy --- 23 lens-A lens Variable --- 24 SN lens MACHO: galaxy --- 25 lens-A lens Clump giant non-LMC 26 SN Variable ------27 lens-B Variable ------The event classification results of MACHO and BEL are compared to the results of additional data that can confirm or reject each event. Confirmed microlensing events have boldface entries in the confirmation column, and rejected microlensing candidates have entries in italics. (Bennett, Becker & Tomaney 2005)

Note that certain data points in the comprised of MACHOs, and concluded table for MACHO, and Evans and with a 95% confidence level that no Belokurov (2005), are in disagreement more than 25% of the halo mass of 4 x 11 with the findings of Bennett et al., 10 Mʘ out to 50 kpc could be however, Bennett et al. reduction and composed of objects between 2 x 10-7 analysis steps appears much improved Mʘ and 1 Mʘ. (Afonso et al. 2003) and refined over earlier studies. A third group represented by the In 2002, the EROS collaborators Optical Gravitational Lensing published the results of five years worth Experiment (OGLE) collaborators chose of data taken toward the SMC applying to look not toward the SMC and LMC, additional reduction steps and analysis to but toward the where low- more accurately assess stellar blending mass stars were known to exist and the on the overall efficiency. The results, microlensing rate was better than one in four additional microlensing candidates, a million with a much better chance of were combined with previous EROS detection. OGLE’s first report observations placing strong limits on the documented nine microlensing events of amount of galactic dark matter galactic bulge stars, but concluded that 9 they had no evidence that the OGLE used as a gravitational telescope to events are related to dark matter discover a source at z = 5.6 (Ellis et al. (Paczynski et al. 1994). They also 2001). A more distant source was later recorded the longest ever microlensing discovered using at z ~ 6.7 event, cataloged OGLE-1999-BUL-32, by Kneib et al. (2004). later verified by MACHO collaborators Gravitational lensing associated with as MACHO-99-BLG-22. The Einstein galaxy clusters reveals the dynamics crossing radius was reported as 640d. supporting the existence of massive dark (Mao et al. 2002) matter halos. The halos associated with One result of the OGLE survey was these galactic clusters, as well as the x- the discovery of an exoplanet through ray emitting intracluster medium (ICM) gravitational lensing. Most extra solar confined to the halo, can be used as a planet discoveries use the radial velocity locator of dark matter. If we assume method in detecting the wobble of the hydrostatic equilibrium within the host star. The planet, designated OGLE- cluster between the gas pressure P and 2005-BLG-390Lb, discovered on July the gravitational potential Φ, the relation 11, 2005, was the third extra solar planet being ∇P = ρg ∇ Φ, with ρg discovered through microlensing. (Türler representing the gas density, the gas 2006) pressure can constrain the shape of the If a summation is to be made . However, the regarding the methods used to detect reliability of the hydrostatic mass dark matter using microlensing within estimates is unknown (Mahdavi et al. the Milky Way galaxy, it is that all 2007). methods employed by collaborators still Elıasdottir et al. (2007) have gone have room for improvement and into great detail in probing the dynamics refinement. The MACHO and EROS of Abell 2218 by explaining and teams have completed the microlensing detailing the mass distribution of dark survey proposed by Paczynski in 1986 matter clumps, based on lensing, of each and concluded that the dark halo of the cluster galaxies. Mass distribution surrounding the Milky Way is not of the cluster galaxies is identified with dominated by planet or stellar mass central locations for the ellipticity and objects, however these mass objects do position angle to the light distribution. exists (Bennett et al. 2005). The total projected mass is centered on a bright central galaxy (BCG) with mass 4. LENSING-BASED SEARCHES FOR distribution bimodal in DM1 (dark DARK MATTER BEYOND THE MILKY matter) and DM2. Referencing Figure 6, WAY GALAXY AND THE KEY the bright BCG is visible, with large RESULTS scale DM1 closely associated with BCG, and DM2 to the southeast (North is up). Galaxy Cluster Abell 2218 was Unfortunately, neither DM1, nor DM2 chosen because of its unusually high z are visible. The clumps are referred to and CL0024+1654 because its mass is as large scale if their total mass in the smaller than the predicted lensing models. outer most constraint is greater than 20% Of all the galaxy clusters in the Abell of the total mass. The team also found catalog, 2218 is one of the richest in evidence that the lensing constraint terms of number of lensing events could not be modeled using only the (Elıasdottir et al. 2007), and has itself been 10

dark matter halos, but required the use of scale halos accounted for 85% of the the large scale halos associated with the total mass, with the BCG ~9% and the dark matter clumps. Within a radius of remaining galaxy clusters ~6% 291 kpc, the team determined that large (Elıasdottir et al. 2007).

Figure 6: Color image of Abell 2218 based on ACS data (filters F775W (red), F625W (green) and F475W (blue) channel ). Cluster galaxies are marked in yellow (modeled using scaling relations) or blue (individually fitted). The multiple images are labeled in green for spectroscopically confirmed systems and red for candidate systems. The arc for which we have obtained spectroscopic redshift, S8, is labeled in cyan. Also shown are the critical lines corresponding to z = 0.702 (cyan), z = 2.515 (red) and z = 6.7 (green). NASA/HST/ACS (Elıasdottir et al. 2007)

In reconstructing a mass map of actually one galaxy twice the distance of Abell 2218, the team of Elıasdottir et al. the foreground cluster, but (2007) confirmed earlier models gravitationally lensed into five images. showing that mass distribution is (Colley et al. 1996) During a five year bimodal, and identifying the cluster as a period starting in 1998, there were strong through inconsistencies in the cluster velocity mapping of large clumps of dark matter. dispersion which was much greater than −1 The rich galaxy cluster the measured value of σv = 1150 km s CL0024+1654 lies approximately five which suggested a flattening of the billion light years distance, and images density profile closer to the core of the show unique blue arclets, which are 11 cluster and in conflict with simulations Mishchenko and Ji (2004) conclude that of the standard CDM model. (Shapiro & sufficient information is not available to Iliev 2000) The inconsistency of the make a quantitative conclusion regarding cluster with the CL0024s thermal state using the known lensing power and X-ray was mass profile. resolved when a second velocity dispersion was found at z ~ 0.38, and has 5. CONCLUSION been suggested was the result of a collision with another galactic group. In the search of dark matter, (Kneib et al. 2003) astronomers and physicists use an array However, Kneib et al. (2003) of instruments and tools. Without suggests that the power law fit indicates knowing what dark matter is, they gather an asymptotic distribution and strongly empirical and measureable facts, and rejects an isothermal mass. Analysis of then conduct experiments and the cluster X-ray emission in 2004 by formulation to test their hypothesis. Ota et al. concluded the mean Tools used include supercolliders to temperature of 4.4 keV was a good fit search for hypothesized subatomic for distribution. Therefore, assuming particles, or neutrino detectors deep that the intracluster medium was in underground. Astronomers look for dark hydrostatic equilibrium, the estimated matter within our Galaxy and throughout mass profile of CL0024 through the Universe by using gravitational gravitational lensing and analysis of the lensing as a tool to measure luminous redshifts of components of the cluster baryonic matter, rotational curves of and X-ray observations indicate a mass 2 stellar objects within galaxies and to to3 times smaller than the lensing mass determine mass distribution. prediction (Coia et al. 2006). It is In addition to ground based interesting to note that studies conducted telescopes, over the years astronomers on CL0024+1654 within the past year have use space based observatories such are referencing data from 1992 as WMAP, Hubble and COBE. Just (Takahashi & Chiba 2007) which is in recently, NASA launched its newest conflict with data mentioned earlier space based observatory, GLAST, with (Kneib et al. 2003). one of its objectives being to look for Kneib et al.(2003) appeared to have gamma rays of specific wavelengths resolved the cluster dispersion problem which are produced by dark matter within CL0024 when a second velocity annihilation. Supersymmetry in particle dispersion peak was found. Referencing physics predicts a particular wavelength their calculations, Mishchenko and Ji of gamma ray is produced through (2004) suggest it is tempting, but WIMP annihilations. These gamma rays incorrect, to correlate equilibrium are distinct for those produced by between the dark and the visible sources such as black holes or components in 0024+1654. To supernovae. (Woo 2008) This is one compensate for the mass loss, they more step toward understanding the suggest dark matter particles with a mass composition of dark matter, and between µd ≈ 200 − 1000MeV and the ultimately the fate of the Universe. Standard Model does not have a candidate within this mass range. 12

The use of gravitational lensing to http://www.spitzer.caltech.edu/Medi detect the presence of dark matter is a/releases/ssc2008-10/release.shtml maturing, but it is not without issues. Coia, D. et al. 2006, A&A, arXiv:astro- All that has been discussed in this ph/0310317v4 paper originates with Einstein’s general Colley, W.N., Turner, E., and Tyson, J.A. theory of Relativity. While not relevant 1994, NASA/HST/WFPC2, to this paper, I want to note that G.B. http://apod.nasa.gov/apod/ap960424.htm l Shaw once said there were only eight Elıasdottir, A. et al. 2007, great men of science, all the others were arXiv:0710.5636v1 [astro-ph], Draft tinkers who chiseled away on the ideas version February 2, 2008 of the eight. And of those eight, there Ellis, R., Santos, M. R., Kneib, J.-P., & were only three who built complete Kuijken, K. 2001, ApJ, 560, L119 universes – Ptolemy, Newton and Evans, N.W., Gyuk, G., Turner, M.S., & Einstein. Binney, J. 1998, ApJ 501:L45–L49 Evans, N.W. & Belokurov, V. 2005, ACKNOWLEDGMENTS submitted to MNRAS, arXiv:astro- This paper was prepared by the author as ph/0505167v1 part of the curriculum requirement of Falco, E.E., Lehar, J., Perley, R.A., ©Swinburne Astronomy Online (SAO), Wambsganss, J., and Gorenstein, M.V., 1996, AJ, .astro-ph/9606048 Graduate Diploma in Science Griest, K. and Thomas, C.L. 2005, MNRAS (Astronomy), Center for Astrophysics & 359, 464-468, arXiv:astro- Supercomputing, Swinburne University ph/0412443v2 of Technology. Thanks to Dr. Chris Halkola, A. et al., 2008, arXiv:0801.1795v1 Fluke (SAO) for critical comments and [astro-ph], Joanie Mickle for editorial comments. http://arxiv.org/PS_cache/arxiv/pdf/080 1/0801.1795v1.pdf REFERENCES Hinshaw, G., et al., 2008, ApJSS, Afonso, C. et al. 2003, A&A 400 951-956 arXiv:0803.0732v1 [astro-ph], arXiv:astro-ph/0212176v2, 28 Jan 2003 referenced parameters for Standard Astier, P., et al., 2006, A&A, 447, 31-48, LCDM Model arXiv:astro-ph/0510447v1 Illingworth, V. & Clark, J.O.E. 2000, The Bally, J. & Reipurth, B. 2006, The Birth of Facts on File Dictionary of Astronomy Stars and Planets, p284-5, (printed in (4th ed.; compiled/typeset by Market China by Imago: Cambridge University House Books, Aylesbury, UK; printed in Press) the U.S.A.; Checkmark Books) Bartelmann, M. and Schneider, P., 2001, Kamionkowski, M., Koushiappas, S.M., manuscript, Max-Planck-Institut fur 2008, arXiv:0801.3269v2 Astrophysik, Garching, Germany, Keel, B., QSO 0957+561, University of http://www.mpa- Alabama, Dept of Astronomy & garching.mpg.de/Lenses/WLRevEls.pdf, Physics, [email protected], Preprint submitted 17 August 2000 www.astr.ua.edu/keel/agn/quasar40.html Bennett, D.P., Becker, A.C., & Tomaney, A. , HST/WFPC2, 3x V&I 2005 ApJ 631:301–311, 2005 Kneib et al. 2003, AsJ 598, 804-817 September 20 arXiv:astro-ph/0307299v1 Clavin, W., California Institute of Kneib, J.-P., Ellis, R. S., Santos, M. R., & Technology, 818-354-4673, Press Richard, J. 2004, ApJ, 607, 697 Release, June 3, 2008 Lang, R., et al., 2008, arXiv:0805.4705v1 13

Livio, M. 2000, The Accelerating Universe: Safonova, M., Torres, D.F., & Romero, Infinite Expansion, the Cosmological G.E., 2001, Mod.Phys.Lett. A16, 153- Constant, and the Beauty of the Cosmos 162, arXiv:astro-ph/0104075v1 (New York, NY: John Wiley & Sons, Shapiro, P.R., & Iliev, I.T., 2000, ApJL, Inc.) p92-3, 95, 109 arXiv:astro-ph/0006353v2 Mahdavi, A., Hoekstra, H., Babul, A., & Sartori, L. 1996, Understanding Relativity: Henry, J.P. 2007, MNRAS, A Simplified Approach to arXiv:0710.4132v2 [astro-ph] Understanding Einstein’s Theories Mao, S. et al., 2002, MNRAS, 329 349, (Berkley & Los Angeles: University of arXiv:astro-ph/0108312v1 California Press) p263, 341 Martin, M., Professor of Physics & Smoot, G. & Davidson, K. 1993, Wrinkles Astronomy, UC Berkeley, in Time (New York: Avon Books, Inc.) http://astro.berkeley.edu/~mwhite/da 170-1 rkmatter/dm.html Szydlowski, M., Tambor, P. 2008, Minniti, D., Dept. of Astronomy & arXiv:0805.2665v1 [gr-qc] Astrophysics, Catholic University of Takahashi, R. & Chiba, T. 2007, AsJ, 671, Chile, presentation, 45-52 http://www.astro.puc.cl/~dante/fia3007 Türler, M. 2006, Cern Courier, Mar 1, macho/macho06/sld005.htm, http://cerncourier.com/cws/article/cern/2 http://fisica.puc.cl//index.php?option=co 9546 m_contact&Itemid=3 Walsh, D., Carswell, R.F., & Weymann, R.J. Mishchenko, Y. & Ji, C-R. 2004, Nova 1979, Nature 279, 381-384 Science Publisher, arXiv:astro- Wambsganss, J., 1998, Gravitational ph/0406563v1 Lensing in Astronomy, © Max-Planck- Nguyen, H.T., Kallivayalil, N., Werner, Gesellschaft. ISSN 1433-8351, M.W., Alcock, C., Patten, B.M., & http://www.livingreviews.org/lrr-1998- Stern, D. 2004, ApJSS, 154:266–270, 12 2004 September Weymann, R.J., Chaffee, F.H. Jr., Carlton, Ota, N., Hattori,M., Pointecouteau, E., & N.P., Walsh, D., Carswell, R.F., Davis, Mitsuda, K. 2004, ApJ, 601, 120 M., 1979, ApJ 233L 43W Paczynski, B. Stanek, K.Z., Udalski, A., Woo, M., 2008, NASA, GLAST website, Szymanski, M., Kaluzny, J., Kubiak, M., http://www.nasa.gov/mission_pages/GL Mateo, M., and Krzeminski, W., 1994, AST/main/index.html arXiv:astro-ph/9407010v3 Zakharov, A.F., Popovic, L.C., & Jovanovic, Riess, A.G., et al., 2004, ApJ. 607, 665-687 P., 2004, A&A 420, 881-888, DOI: arXiv:astro-ph/0402512v2 10.1051/0004-6361:20034035