Chandra Sivaram

In view of the negative results from various dark matter detection experiments, we had earlier proposed an alternate theoretical framework through modification of Newtonian gravity (MONG). Here, the Poison’s equation is modified by introducing an additional gravitational self-energy density term along with the usual dark energy density term. In this work, we extend this model to account for the presence of low-density gas at high temperatures [ ] in the intra cluster medium (ICM) by estimating the velocities to which particles will be subjected by the modified gravitational force. Considering that the ICM is under the influence of the cluster’s gravity, particle velocities of the ions in the ICM must be balanced by the cluster’s gravitational force. The particle velocities obtained for various clusters from their temperature profiles match the velocity produced by the MONG gravitational force. Thus, the increase in the gravitational potential at the outskirts of galaxies balances the thermal pressure of the ICM, maintaining hydrostatic equilibrium without invoking DM. The effect of MONG on the angular momentum of galaxies is also studied by obtaining a scaling relation between the angular momentum and the mass of a galaxy. MONG predicts a higher dependence on mass in comparison to the [ ] CDM model. This increased dependence of angular momentum on mass compensates for the halo contribution to the angular momentum. The angular momentum from MONG for galaxies from the spritzer photometry and accurate rotation curves (SPARC) database is compared to the halo angular momentum by a chi-square fit technique. The correlation coefficient is found to be unity, showing a replicable result.

The estimation of the Hubble constant in the past few decades has increasingly become more accurate with the advancement of new techniques. However, its value seems to depend on the epoch at which the measurements are made. The Planck estimate of the Hubble constant from the observations of the cosmic microwave background radiation in the early universe is about [ ], whereas that obtained from the distance indicators at the current epoch is [ ]. This discrepancy between the two groups of measurement is termed as the Hubble tension which has gained much attention in the past few decades with growing significance as measurements from both, the early and the late universe, studies continue to produce results with increasing precision. In this work, we propose a modification to gravity by considering a finite range gravitational field as an alternate explanation for this discrepancy in the value of the Hubble constant.

The definitive negative results of various direct searches for dark matter particles and non-observation of them has increasingly indicated that we should consider alternate models like the Modification of Newtonian Dynamics (MOND) and Modification of Newtonian Gravity (MONG). It is puzzling how the Oort cloud, despite its great distance from the Sun, is gravitationally bound to the Sun’s gravity. In this work, we suggest that this could be explained by the modifications to Newtonian dynamics (MOND) and to gravity (MONG).

Polyhymnia (33 Polyhymnia) is a main belt asteroid in our solar system with a diameter of around 54km. The density of asteroid 33 Polyhymnia, located in the main asteroid belt, is calculated to be 75g/cc. Researchers have speculated the possibility that Polyhymnia could be composed of high-density superheavy elements near atomic number 164. Here we propose that Polyhymnia could be an asteroid composed of degenerate Dark Matter (DM) and there could be many such asteroids in our solar system (this is following our earlier work suggesting Planet Nine could be such an object).

It has been suggested that primordial planets could have formed in the early universe and the missing baryons in the universe could be explained by primordial free-floating planets of solid hydrogen. Many such planets were recently discovered around the old and metal-poor stars, and such planets could have formed in early epochs. Another possibility for missing baryons in the universe could be that these baryons are admixed with DM particles inside the primordial planets. Here, we discuss the possibility of the admixture of baryons in the DM primordial planets discussed earlier. We consider gravitationally bound DM objects with the DM particles constituting them varying in mass from 20 to100 GeV. Different fractions of DM particles mixed with baryonic matter in forming the primordial planets are discussed. For the different mass range of DM particles forming DM planets, we have estimated the radius and density of these planets with different fractions of DM and baryonic particles. It is found that for heavier-mass DM particles with the admixture of certain fractions of baryonic particles, the mass of the planet increases and can reach or even substantially exceed Jupiter mass. The energy released during the process of merger of such primordial planets is discussed. The energy required for the tidal breakup of such an object in the vicinity of a black hole is also discussed.

In recent works we had discussed the possibility of primordial planets composed entirely of dark matter (DM), and considered this to be a possible reason for not detecting DM particles in the various ongoing experiments. It has been suggested that such primordial DM objects could have formed in the early universe. Here we look at these DM objects as possible candidates for short duration gamma ray bursts. This model has the advantage of eliminating the as yet unresolved baryon load problem in the usual scenario. These could also provide a possible mechanism for the formation of sub-stellar black holes, distinct from the usual Hawking (primordial) black holes.

It has been suggested that primordial planets could have formed in the early Universe and the missing baryons in the Universe could be explained by primordial free-floating planets of solid hydrogen. Many such planets were recently discovered around the old and metal poor stars and such planets could have formed at early epochs. Another possibility for missing baryons in the Universe could be that these baryons are admixed with DM particles inside the primordial planets. Here we discuss the possibility of admixture of baryons to the DM primordial planets discussed earlier. We consider gravitationally bound DM objects with the DM particles constituting them varying in mass from 20 to100GeV. Different fractions of DM particles mixed with baryonic matter in forming the primordial planets are discussed. For the different mass range of DM particles forming DM planets, we have estimated the radius and density of these planets with different fractions of DM and baryonic particles. It is found that for heavier mass DM particles with the admixture of certain fractions of baryonic particles, the mass of the planet increases and can reach or even substantially exceed Jupiter-mass. The energy released during the process of merger of such primordial planets is discussed. Also the energy required for the tidal breakup of such an object in the vicinity of a black hole is also discussed.

Black Holes are not expected to form in the mass range of 60 M_⊙ to 130 M_⊙ because of the Pair-Instability Supernova (PISN). However, the recent observational evidence of GW190521 does not comply with the existing theory. Here, we have looked into the effects of Dark Matter (DM) in the progenitors of PISN in terms of luminosity, lifetime and temperature and have shown that in the presence of DM particles, the progenitors can overcome the PISN stage to collapse into a black hole (BH) as a remnant.