Our universe is becoming more mysterious with the attempts of understanding it deeply. The Galaxies are moving away from each other because of expanding universe which is now well accepted concept. Now, the astronomers have also observed that the galaxy clusters are constantly moving towards a point present in southern constellation Centaurus and Hydra. The source of this attraction is doubted to be present outside our observable universe. The astronomers have no idea what is causing this mysterious motion of galaxy clusters, they are just calling it “Dark Flow”.
The research led by Alexander Kashlinsky at NASA’s Goddard Space Flight Center in Greenbelt, Md., is based on the study of motion of large galaxy clusters which are present at very large distances ranging from hundred million light years to 6 billion light years. Evidences indicate that the galaxy clusters are heading outward with the tremendous velocity of 2 million mph along the line joining the Earth and the constellation Hydra. This motion is independent of the expansion of universe. The direction of motion is still not certain, outward motion cannot be neglected. “We detect motion along this axis, but right now our data cannot state as strongly as we’d like whether the clusters are coming or going,” Kashlinsky said.
The Dark Flow is mysterious because present distribution of mass in our universe do not account for this, it indicates presence of some external source outside our universe influencing and sweeping matter from our vicinity. These shocking results were obtained in study of Cosmic Microwave Background (CMB) radiation which is believed to be emitted 380,000 years after the formation of the universe. CMB is prevailed the whole universe, the study of fluctuations due to interaction between CMB and galaxy cluster provides information about the motion of galaxy clusters.
The X-ray emitting hot gases of galaxy cluster scatters the photons of the CMB which results in the decrease in the temperature of CMB in the direction of galaxy. This is called kinematic Sunyaev-Zel’dovich (KSZ) effect. The dipoles in CMB change in such a way that it indicates the motion of individual cluster. The measurement of wavelength of scattered photon can be used to calculate the speed and direction of motion of cluster. The shift in temperature of CMB due to one cluster is negligible and cannot be detected easily. In 2000, Kashlinsky along with Fernando Atrio-Barandela at the University of Salamanca, Spain showed that the noise from the signals can be removed if they study large number of galaxy clusters. Via Dark Flow From Other Universe Engulfing Galaxy Clusters | CosmosUp.