Research Papers (TP)
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Item Gravitational perturbation of homogeneous collisionless dark matter(Indian Academy of Sciences, 1985-08-12) Padmanabhan, T.; Vasanthi, M. M.The effect of a perturbing mass on a homogeneous collisionless cloud of dark matter is considered in the linear approximation. It is shown by that gravitational potential can have turning points, in sharp contrast with gravitating system of finite extent. The model offers a reasonable explanation for the observed secondary maxima in the destiny distribution of rich clusters . The relevance of the model to the flatness of the rotation curves of galaxies is also discussed.Item Nature and distribution of dark matter: 2. Groups and clusters(Indian Academy of Sciences, 1989-08-11) Vasanthi, M. M.; Padmanabhan, T.We study the mass-radius relationship for aggregates of galaxies, viz. binaries, small groups and clusters. The data are subjected to a simple best-fit analysis similar to the one carried out earlier for individual field galaxies. The analysis shows that: (i) The data on binary galaxies are consistent with the assumption that binaries are just two galaxies, each with an individual isothermal (M∝R) dark matter halo, moving under the mutual gravitational attraction, (ii) The data on the groups of galaxies are too scattered to obey a single power-law relation of the form M = kRᶯ with any degree of reliability, (iii) The data on groups and clusters fit better with a law of the form M = AR³ +BR. This form suggests the existence of two components in dark matter-one which is clustered around the galaxies (M∝R) and another which is distributed smoothly (M∝R3). The smooth distributions becomes significant only at scales ≥ 1 Mpc and hence does not affect binaries significantly. We briefly discuss the theoretical implications of this analysis.