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Astronomy

Astronomy is an international, peer-reviewed, open access journal on observational astronomy, theoretical astronomy and other specific subfields published quarterly online by MDPI.

All Articles (73)

On the Possible Nature of White Holes

  • Mikhail Pekker and
  • Mikhail N. Shneider

This paper considers non-singular black holes. It discusses the observation of particles falling onto ordinary and non-singular black holes from the perspective of a distant observer. It is demonstrated that, during a stage in the evolution of non-singular black holes, powerful energy fluxes can be emitted. Distant observers may interpret these fluxes as white holes.

10 October 2025

Schematic representation of a false vacuum droplet in a gravitating environment. Note that this distribution is similar to the hypothetical gravastar objects, which are an alternative to black holes (see, for example, [16,17]).

The subject of boosted fluxes of dark matter or cosmic relic neutrinos via scattering on cosmic rays has received considerable attention recently. This article investigates the boosted neutrino flux from the scattering of cosmic rays and the so-far undetected diffuse supernova neutrino background, taking into account both galactic and extragalactic cosmic rays. The calculated flux is many orders of magnitude smaller than either the galactic diffuse neutrino emission, the extragalactic astrophysical flux measured by IceCube, or the cosmogenic neutrino flux expected at the highest energies.

12 September 2025

Fiducial spectrum of the diffuse supernova neutrino background from [10] based on simulations in [11]. The spectrum is weighted with the square of the neutrino energy.

We extend the Quantum Memory Matrix (QMM) framework—previously shown to unify gauge interactions and reproduce cold dark matter phenomenology—to account for the observed late-time cosmic acceleration. In QMM, each Planck-scale cell carries a finite-dimensional Hilbert space of quantum imprints. We show that (1) once local unitary evolution saturates the available micro-states, a uniform residual “vacuum-imprint energy” remains; its stress–energy tensor is of pure cosmological-constant form, with magnitude suppressed by the cell capacity, naturally yielding ρΛ(2×103eV)4; and (2) if imprint writes continue but are overdamped by cosmic expansion, the coarse-grained entropy field S(t) undergoes slow-roll evolution, generating an effective equation of state that is testable by DESI, Euclid, and Roman. We derive the modified Friedmann equations, linear perturbations, and joint constraints from Planck 2018, BAO, and Pantheon +, finding that the QMM imprint model reproduces the observed TT, TE, and EE spectra without introducing additional free parameters and alleviates the H0 tension while remaining consistent with the large-scale structure. In this picture, dark matter and dark energy arise as gradient-dominated and potential-dominated limits of the same underlying information field, completing the QMM cosmological sector with predictive power and internal consistency.

10 September 2025

Numerical slow-roll solution for the QMM entropy field. The linear rise of 
  
    S
    (
    t
    )
  
 is characteristic of the overdamped regime, whereas 
  
    S
    ˙
  
 and the driving term 
  
    Γ
    (
    t
    )
  
 stay tiny on the same scale.

Calibrating the ages, masses, and radii of stars on the upper main sequence depends heavily on accurate measurements of the effective temperature (Teff) and surface gravity (logg). These parameters are difficult to obtain meticulously due to the nature of hot stars, which exhibit features such as rapid rotation, atomic diffusion, pulsation, and stellar winds. We compare the Teff and logg values of apparent normal B-F stars in four recent catalogues that employ different methods and pipelines to obtain these parameters. We derived various statistical parameters to compare the differences between the catalogues and discussed the astrophysical implications of these differences. Our results show that the huge differences in Teff (up to 104 K) and logg (up to 2 dex) between the catalogues have serious implications on the determination of ages, masses, and radii of the stars in question. We conclude that there appears to be no homogeneous set of stellar parameters on the upper main sequence, and one must be cautious when interpreting results obtained from using only one of the catalogues. The homogenisation of said parameters is an essential task for the future and will have a significant impact on astrophysical research dealing with stars on the upper main sequence.

22 August 2025

Kiel diagrams for the different catalogues we used.

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Astronomy - ISSN 2674-0346Creative Common CC BY license