Gravitational collapses and Hilbertian repulsion

If we take into account the Hilbertian gravitational repulsion, even a dust sphere with a zero fluido-dynamical pressure collapses to a body of a comparatively small, finite, volume.Comment: 4 pages, LaTe

On the GR-speeds of light and particles (A remembrance of things past)

There are no limits for the speeds of light and particles in general relativity (GR). Four examples illustrate this basic result, which is too often neglected.Comment: 5 page

All relativistic motions can be geodesically described

A suitable choice of the four components of the metric tensor which are at our discretion allows to represent geodesically also the non-gravitational motions.Comment: 3 pages, LaTe

On the gravitational collapse of a massive star

The celebrated treatment of continued gravitational collapse by Oppenheimer and Snyder is revisited and emended from some inherent flaws. The star contracts itself into a material point, not into a black hole.Comment: 7 pages, LaTex, to be published on Spacetime & Substanc

Protons do not exert any Hilbertian gravitational repulsion

The Hilbertian gravitational repulsion is quite absent in the Einsteinian field of a proton, owing to the gravitational action of its electric charge. Accordingly, the proton bunches of the LHC cannot exert any repulsive gravitational force.Comment: 3 pages, Late

On the gravitational redshifts of spectral lines - A critico-historical study

A beautiful, detailed computation by Whittaker has enabled us to prove in a rigorous way that the gravitationally redshifted frequency of a monochromatic e.m. wave sent forth at the surface of a celestial body is propagated unaltered from the emitting source to terrestrial observers. We remark that in the customary treatments only qualitative and inaccurate justifications of this fact are given.Comment: 9 page

Remarks on numerical relativity, geodesic motions, binary neutron star evolution

The computations of numerical relativity make use of (3+1)- decompositions of Einstein field equations. We examine the conceptual characteristics of this method; instances of compact-star binaries are considered. The preeminent role of the geodesic motions is emphasized.Comment: 8 page

On Majorana's equation

The physical results of quantum field theory are independent of the various specializations of Dirac's gamma-matrices, that are employed in given problems. Accordingly, the physical meaning of Majorana's equation is very dubious,considering that it is a consequence of ad hoc matrix representations of the gamma-operators. Therefore, it seems to us that this equation cannot give the equation of motion of the neutral WIMPs (weakly interacting massive particles), the hypothesized constitutive elements of the Dark Matter.Comment: 4 page

The supermassive centre of our galaxy - et cetera

We show that the supermassive celestial body at the centre of the Milky Way and the two supermassive celestial bodies at the centre of the distant galaxy NGC 6240 cannot be black holes.Comment: 3 pages, LaTeX, to be published on Spacetime & Substanc

On some relativistic singular surfaces

In the current relativistic literature there are misleading considerations about some singular surfaces. An accurate geometric analysis allows to settle the question. No physical meaning is attributable to the spatial regions surrounded by the above surfaces. A recent observational paper by A. Fabian et al. is discussed in sect.4.Comment: 5 pages, LaTe