Mohamad-Ziad Charif - Antares

Figure 2.3: Diagram on the apparent and real path of light around a massive object.that of the visible mass being located in a dark halo surrounding the clusters.Additionally the measurement of the mass to light ratio showed that the value ismuch larger than the average of the individual components indicating again thatthere is at least 3 times more invisible matter than visible.2.1.5 Cosmic microwave backgroundThe Cosmic Microwave Background (CMB) is thermal radiation (∼ 2.725K) thatpermeates with a high degree of uniformity the observable universe. The CMBwas first theorized in 1948 as the thermal residual of the big bang and its detectionwas delayed until 1964. Since that several experiments were built to measurethe CMB radiation such as COBE experiment[15], WMAP[16] (figure 2.4), andPLANCK[17].While CMB is not in itself evidence for dark matter, it validates the ΛCDM model(section 2.1.6 ) which predicts the existence of dark matter. The model is furthervalidated by other measurement such as the Baryon acoustic oscillations[18],distance measurements by type Ia supernovae[19], and the Lymann-alpha forestmeasurements[20] (Figure 2.5).2.1.6 ΛCDM modelThe ΛCDM model is referred to as the Standard Model of cosmology, the modelis built on solutions to Einstein equation of General Relativity (eq 2.1)Where:R µν − R 2 g µν − Λg µν = 8πT µν (2.1)9