Major merging of galaxies in multicomponent numerical models: mass loss and exchange

The process of collision of two multicomponent galaxies is considered in detail based on numerical simulations of the dynamics of gravitating gas, stars and dark mass. To solve the equations of motion of the gas component, we use the Smoothed Particle Hydrodynamics method. Modeling of collisionless components is based on the N-body model. The computations of gravitational forces are carried out using both the approximate hierarchical TreeCode algorithm and the direct method of summing the gravitational contribution from all particles, which provides an accurate solution. This approach allows testing various models and evaluating the resulting errors associated with the calculation of gravitational forces and a finite number of particles in each of the components. Both methods for calculating gravity are software implemented as parallel codes for Nvidia Tesla GPUs. The estimates of the lost mass and the efficiency of matter exchange between galaxies are discussed depending on the model parameters.

A Poynting theorem formulation for the gravitational wave stress pseudo tensor

A very simple and physical derivation of the conservation equation for the propagation of gravitational radiation is presented. The formulation is exact. The result takes the readily recognisable and intuitive form of a Poynting-style equation, in which the outward propagation of stress energy is directly related to the volumetric equivalent of a radiation reaction force acting back upon the sources, including the purely gravitational contribution to the sources. Upon averaging, the emergent pseudo tensor for the gravitational radiation is in exact agreement with that found by much more labour-intensive methods.

Revisiting the scalar weak gravity conjecture

We revisit the scalar weak gravity conjecture and investigate the possibility to impose that scalar interactions dominate over gravitational ones. More precisely, we look for consequences of assuming that, for leading scalar interactions, the corresponding gravitational contribution is sub-dominant in the non-relativistic limit. For a single massive scalar particle, this leads us to compare four-point self-interactions in different type of potentials. For axion-like particles, we retrieve the result of the axion weak gravity conjecture: the decay constant f is bounded by the Planck mass, $$f < {M_{Pl}}$$f<MPl. Similar bounds are obtained for exponential potentials. For quartic, power law and Starobinsky potentials, we exclude large trans-Planckian field excursions. We then discuss the case of moduli that determine the scalars masses. We retrieve the exponential dependence as requested by the Swampland distance conjecture. We also find extremal state masses with field dependence that reproduces both the Kaluza-Klein and winding modes behaviour. In particular cases, our constraints can be put in the form of the Refined de Sitter Conjecture.

On testing CDM and geometry-driven Milky Way rotation curve models with Gaia DR2

ABSTRACT Flat rotation curves (RCs) in disc galaxies provide the main observational support to the hypothesis of surrounding dark matter (DM). Despite of the difficulty in identifying the DM contribution to the total mass density in our Galaxy, stellar kinematics, as tracer of gravitational potential, is the most reliable observable for gauging different matter components. From the Gaia second data release catalogue, we extracted parallaxes, proper motions, and line-of-sight velocities of unprecedented accuracy for a carefully selected sample of disc stars. This is the angular momentum supported population of the Milky Way (MW) that better traces its observed RC. We fitted such data to both a classical, i.e. including a DM halo, velocity profile model, and a general relativistic one derived from a stationary axisymmetric galaxy-scale metric. The general relativistic MW RC results statistically indistinguishable from its state-of-the-art DM analogue. This supports the ansatz that a weak gravitational contribution due to the off-diagonal term of the metric, by explaining the observed flatness of MW’s RC, could fill the gap in a baryons-only MW, thus rendering the Newtonian-origin DM a general relativity-like effect. In the context of Local Cosmology, our findings are suggestive of the Galaxy’s phase space as the exterior gravitational field in equilibrium far from a Kerr-like inner source, possibly with no need for extra matter to account for the disc kinematics.

Contributions to Jupiter's gravity field from dynamics in the dynamo region and deep atmosphere

&lt;p&gt;The antisymmetric part of Jupiter's zonal flows is responsible for the large odd gravity harmonics measured by the Juno spacecraft. Here, we investigate the contributions to Jupiter's odd gravity harmonics (&lt;em&gt;J&lt;sub&gt;3&lt;/sub&gt;&lt;/em&gt;, &lt;em&gt;J&lt;sub&gt;5&lt;/sub&gt;&lt;/em&gt;, &lt;em&gt;J&lt;sub&gt;7&lt;/sub&gt;&lt;/em&gt;, &lt;em&gt;J&lt;sub&gt;9&lt;/sub&gt;&lt;/em&gt;) from dynamics in the dynamo region and the deep atmosphere. First, we estimate the odd gravity harmonics produced by zonal flows in the dynamo region. Using Ferraro's law of isorotation, we construct physically motivated profiles for dynamo region zonal flow. We use the vorticity equation to determine the density perturbations associated with the flows and then calculate the odd gravity harmonics. We find that dynamo zonal flows with root mean square (RMS) velocities of 10 cm/s would produce &lt;em&gt;J&lt;sub&gt;3&lt;/sub&gt;&lt;/em&gt; values on the same order of magnitude as the Juno measured value, but would not significantly contribute to &lt;em&gt;J&lt;sub&gt;5&lt;/sub&gt;&lt;/em&gt;, &lt;em&gt;J&lt;sub&gt;7&lt;/sub&gt;&lt;/em&gt;, and &lt;em&gt;J&lt;sub&gt;9&lt;/sub&gt;&lt;/em&gt;. Next, we examine the gravitational contribution from zonal flows above the dynamo region. We consider a simple model where the observed surface winds are barotropic (i.e., &lt;em&gt;z&lt;/em&gt;-invariant) until they are truncated at some depth by some dynamical process, such as stable stratification and/or MHD processes. We find that barotropic zonal flow in the strongly antisymmetric northern (13&amp;#176;-26&amp;#176;N) and southern (14&amp;#176;-21&amp;#176;S) jets extending to the likely depth of a rock cloud layer or deep radiative zone can account for a significant fraction of the observed gravity signal.&lt;/p&gt;

The aesthetics of verticality: A gravitational contribution to aesthetic preference

Verticality plays a fundamental role in the arts, portraying concepts such as power, grandeur, or even morality; however, it is unclear whether people have an aesthetic preference for vertical stimuli. The perception of verticality occurs by integrating vestibular-gravitational input with proprioceptive signals about body posture. Thus, these signals may influence the preference for verticality. Here, we show that people have a genuine aesthetic preference for stimuli aligned with the vertical, and this preference depends on the position of the body relative to the gravitational direction. Observers rated the attractiveness of lines that varied in inclination. Perfectly vertical lines were judged to be more attractive than those inclined clockwise or anticlockwise only when participants held an upright posture. Critically, this preference was not present when their body was tilted away from the gravitational vertical. Our results showed that gravitational signals make a contribution to the perception of attractiveness of environmental objects.