Abstract
The presence of exotic states of matter in neutron stars (NSs) is currently an open issue in physics. The appearance of muons, kaons, hyperons, and other exotic particles in the inner regions of the NS, favoured by energetic considerations, is considered to be an effective mechanism to soften the equation of state (EoS). In the so-called two-families scenario, the softening of the EoS allows for NSs characterized by very small radii, which become unstable and convert into a quark stars (QSs). In the process of conversion of a NS into a QS material can be ablated by neutrinos from the surface of the star. Not only neutron-rich nuclei, but also more exotic material, such as hypernuclei or deconfined quarks, could be ejected into the atmosphere. In the NS atmosphere, atoms like H, He, and C should exist, and attempts to model the NS thermal emission taking into account their presence, with spectra modified by the extreme magnetic fields, have been done. However, exotic atoms, like muonic hydrogen (p μ−) or the so-called Sigmium (Σ+ e−), could also be present during the conversion process or in its immediate aftermath. At present, analytical expressions of the wave functions and eigenvalues for these atoms have been calculated only for H. In this work, we extend the existing solutions and parametrizations to the exotic atoms (p μ−) and (Σ+ e−), making some predictions on possible transitions. Their detection in the spectra of NS would provide experimental evidence for the existence of hyperons in the interior of these stars.
Highlights
In this work we propose a novel approach to attempt the identification of hyperons and other exotic particles in neutron stars (NSs): the search for signals of the possible formation of exotic atoms in the atmosphere of NS in the process of conversion into a quark star (QS) through the spectroscopic study of their radiation emission
Under the condition of a strong magnetic field B, atoms are of cylindrical shape, and that the traditional level structure observed in terrestrial experiments is superseded by a much simpler structure of Landau levels with principal quantum number n, with two additional quantum numbers for each level: m, which corresponds to the angular momentum projection on the field axis, and ν, which quantizes the motion along B
The main result of these analyses is that the combustion proceeds in two phases: a first rapid burning, accelerated by hydro-dynamical instabilities, lasting only a few milliseconds and converting the core of the star, followed by a much slower combustion driven by diffusion of strange quarks from the burnt into the unburnt region, lasting few tens of seconds
Summary
The observation of two NSs with masses as high as 2 M [4, 5] seems to exclude the presence of exotic particles in the core of the star, based on what we know about the interaction between these particles and normal nucleons. This apparent inconsistency, usually referred to as hyperon puzzle, is due to the poor knowledge of the interactions involved in these exotic states of matter and to the difficulty of obtaining clear evidence of their presence in NSs from astrophysical observations. The evaluation of hypothetical new spectral lines, corresponding to transitions among these levels, could offer alternative interpretations of the anomalies seen in the existing data and/or suggest new observational strategies
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