Dark matter wouldn’t behave as expected more than 8 billion years ago

It took twenty years to demonstrate the existence of neutrinos and about forty for that of Brout-Englert-Higgs boson. How much longer will it take to demonstrate the existence of particles of black matter or on the contrary to demonstrate their non-existence?

Recall that the neutrino had been postulated by Wolfgang Pauli to maintain the law of conservation of energy in certain nuclear decays which seemed to violate it. But for that it was necessary to admit that the energy which seemed to disappear into nothingness was in fact carried away by a particle without mass, with no electrical charge and interacting so little with low-energy matter that it could traverse 300 Earths without stopping. We know today that there are in fact three types of neutrinos and that they have masses, although very small.

Dark matter particles are just as ghostly, but paradoxically we need them to account for the existence of galaxies and structures that bring them together in the form of clusters containing from a few hundred to a few thousand galaxies very roughly. It is under the effect of their field of gravitation that ordinary matter collapsed faster than it should have on its own. We know for various reasons that these particles of dark matter do not resemble those which we know on Earth and which are in particular produced in the collisions of protons to LHCalthough they are precisely tracked there.

However, even though dark matter is one of the pillars of Standard cosmological modelit could not exist and the observations of which it reports could perhaps also be explained by modifying the equations celestial mechanics Newton. One wonders currently if the first discoveries of galaxies which seem very primitive by the telescope James-Webb, because observed as they were more than 13 billion years ago, are not precisely a beginning of a refutation of the dark matter theory and a confirmation of the Mond theory.

A new surprise in this regard may be nearing the end of its nose in an article published in Physical Review Letters by an international team of researchers led by members of Nagoya University in Japan. It deals with certain results obtained with the Japanese Subaru telescope, in Hawaii, within the framework of the research campaign of the Subaru Hyper Suprime – Cam Survey (HSC), in combination with other observations obtained by the Planck satellite of the’ESA in the form of his famous map of cosmic radiationthe oldest light of the’Universe observable, emitted about 380,000 after the big Bang in a few thousand years.

Dark matter that distorts images of galaxies

Let us also remember what the astrophysicist and cosmologist Laurence Perotto, member of the Planck collaboration, had explained to Futura in the file that she had allowed us to write where she explained to us the nature of the fossil radiation and the analyzes that she and her colleagues had planned to make of this radiation in search of fundamental keys for the cosmology and the physical theoretical: ” The effect of gravitational lens makes it possible to reconstruct the integrated gravitational potential of the surface of the last diffusion till today. It is an interesting probe of the structures of the Universe. Thus, if we succeed in this reconstruction, Planck would become an autonomous experiment sensitive to the whole evolution of the Universe, from the primordial universe of the time of the last diffusion until us. “.

The surface of last scattering is that of a fictitious sphere surrounding any observer in the cosmos observable and showing him the regions from which the photons of the fossil radiation when the observable Universe became transparent because its density became so low that the photons of that time could, from then on, travel without colliding with charged particles which would scatter them over large distances.

The evoked gravitational lens effect, in this case the so-called weak one or even gravitational shear, is an effect of deflection of light rays by a gravitational field leading to deformation of the initial image of a galaxy by a large mass interposed between this galaxy and an observer. We can deduce from the deformation the mass of the body producing it, so that measuring gravitational lensing effects makes it possible to probe mass distributions in the observable cosmos, including masses of dark matter which itself does not radiate.

This effect has been used to estimate the presence and distributional changes of dark matter up to about 8 to 10 billion years ago. As Laurence Perotto also explained to us, the weak gravitational lensing effects produced by cluster of galaxies and the galaxies in the foreground of the last scattering surface contaminate the study of the fossil radiation and it is necessary to somehow subtract this noise from the signal to go back to the primitive state of the fossil radiation. This makes it possible in particular to track down the mythical B-mode primitives of the polarization of the fossil radiation. The highlighting of these modes would convincingly demonstrate the existence of a vertiginous inflationary phase of the expansion of space during the Big Bang.

Clusters of dark matter that have been structured since the Big Bang

But, as the cosmologist had mentioned in the excerpt from her file that we have given, the measurement of the weak gravitational lensing effect could in theory inform us about the presence and the variable characteristics over time and space of dark matter from the appearance of the first galaxies until today using fossil radiation.

The Japanese-led team managed to make precisely such observations beyond 8 billion years by measuring the effects of galaxies detected with the HSC on Planck’s measurements of the background radiation. We had not gone further before because the galaxies, whose images were distorted by gravitation, were too faint to make valid measurements.

But now researchers can go back about 12 billion years into the observable cosmos.

Remarkably, although still to be confirmed, the size characteristics of dark matter concentrations between 8 and 12 billion years ago do not seem to follow the predictions of the Standard cosmological modelthe dark matter density fluctuations during this period appear weaker than expected.

Yuichi Harikaneone of the authors of the discovery and Professor at theInstitute for Cosmic Ray Research from the University of Tokyo, does not hesitate to explain: ” Our conclusion is still uncertain. But if true, that would suggest that the whole model is flawed as you go back further in time. It’s exciting because if the result holds after reducing the uncertainties, it could suggest an improvement in the model that could provide the nature of dark matter itself. »

With this goal in mind, cosmologists still need to increase the volume and accuracy of available data, which they will soon be able to do with the commissioning of the Vera C. Rubin Observatory, formerly called the OHSA.