arXiv subjects

Sergij Mazurenko

Publications and source records attributed to Sergij Mazurenko.

5 recordsLinked to original sources

arXiv2026

The local void model for the Hubble and BAO tensions

The inconsistency between the locally inferred Hubble constant and the value inferred from the cosmic microwave background assuming the $Λ$CDM cosmological model has persisted, turning into an important problem. An emergent underlying trend is that this Hubble tension is driven by data confined to the very low-redshift Universe (typically $z < 0.15$). Most intermediate-redshift measurements remain mutually consistent with $H_0^\mathrm{CMB}$, the $Λ$CDM expectation anchored by the CMB. This Perspective examines if a large local void can explain the Hubble tension and its appearance only at low $z$. For an observer residing within a large underdensity, such as the Milky Way inside the claimed KBC void, gravitationally induced outflows and redshift can inflate the locally inferred recession scale $cz'$ despite having $H_0 = H_0^\mathrm{CMB}$. We summarise evidence suggestive of a local underdensity from multi-wavelength galaxy number counts, discuss the dynamical requirements implied by the amplitude of inferred bulk flows, and connect the solution to the emerging low-redshift BAO distance anomaly ($α_{\mathrm{iso}} < 1$). Previously published semi-analytic void models anticipated the observed redshift dependence of BAO deviations and predict a rapid convergence to CMB-consistent expansion for $z \gtrsim 0.2$, aligning with reconstructions of $H_0(z)$ from BAO plus uncalibrated Type Ia supernovae. We conclude by looking to future tests, including improved mapping of the local density and velocity field, fits to galaxy distance catalogues at the field level, kinematic Sunyaev-Zel'dovich constraints on coherent outflows, fast radio bursts, and the long-term prospect of redshift drift measurements as a direct probe of time-varying non-cosmological redshift contributions.

astro-ph.CO↗

arXiv2026

Intermediate-mass black hole incubators. Gas accretion onto stellar black hole clusters in galactic central molecular zones

The stellar dynamical evolution of massive star clusters formed during starburst periods leads to the segregation of $\gtrsim10^4 M_\odot$ stellar-mass black hole sub-clusters in their centres. In gas-rich environments, such as galactic central molecular zones, these black hole clusters are likely to accrete large amounts of the gas from their surroundings, which in turn affects their internal dynamics. In this Letter we estimated the corresponding accretion rate onto the black hole cluster and its radiative feedback. We assessed whether such an accretion flow can lead to the collapse of the black hole cluster into an intermediate-mass black hole. The estimates were obtained analytically, considering the astrophysical conditions and star formation history reported for the central molecular zone of our Galaxy. We find that a stellar black hole cluster with mass $\gtrsim10^4 M_\odot$ located in the twisted ring of molecular clouds with radius $\approx100$ pc that is observed in the central molecular zone of our Galaxy can accrete about the same mass in gas on a timescale of a few million years. We suggest that this is sufficient for its subsequent collapse into an intermediate-mass black hole. Based on an estimate of the dynamical friction inspiral time, we further argue that the locations of the intermediate-mass black hole candidates recently observed in the central molecular zone are compatible with their formation therein during the last starburst period reported to have occurred $\approx1$ Gyr ago.

astro-ph.GA↗

arXiv2025

The redshift dependence of the inferred $H_0$ in a local void solution to the Hubble tension

Galaxy number counts suggest that we are located within the Gpc-scale KBC void. The Hubble tension might arise due to gravitationally driven outflow from this void, as explored in detail by Haslbauer et al. We explore how the impact of the void on redshift decays at large distances. We define $H_0(z)$ as the present expansion rate $H_0$ that would be inferred from observations in a narrow redshift range centred on $z$. We find $H_0(z)$ in three different ways, all of which give similar results. We then compare these results with the observations of Jia et al., who were careful to minimise the impact of correlations between $H_0$ measurements from data in different redshift bins. We find reasonable agreement with their results for the Gaussian and Exponential void underdensity profiles, although the agreement is less good in the Maxwell-Boltzmann case. The latter profile causes severe disagreement with the observed bulk flow curve at $z < 0.1$ (Mazurenko et al.), so the tension with higher redshift data further highlights that the deepest part of the KBC void is probably near its centre. The observations show a decline of $H_0(z)$ towards the background $Planck$ value in qualitative agreement with the considered models, even if we use a larger void. The good overall agreement with the recent results of Jia et al. suggests that the local supervoid evident from the galaxy luminosity density out to a Gpc might also solve the Hubble tension while retaining a low background $H_0$ consistent with $Planck$ data, assuming enhanced structure formation on $>100$ Mpc scales.

astro-ph.CO↗

arXiv2024

Open star clusters and their asymmetrical tidal tails

Stars that evaporate from their star cluster by the energy equipartition process end up either in a leading or a trailing tidal tail. In Newtonian gravitation and for open star clusters in the Solar vicinity, the tidal threshold, or prah, for escape is symmetrical, such that the leading and trailing tails are equally populated. The data by six independent teams that applied the convergent point method to map out the tidal tails of four open clusters (the Hyades, the Praesepe, Coma Berenices and COIN-Gaia13) using Gaia DR2 and DR3 are here applied to test for the expected symmetry. All tidal tails contain more stars in the leading tail. The combined confidence amounts to an 8 sigma falsification of the prah symmetry. The same test using Milgromian dynamics leads to consistency with the data. More effort needs to be exerted on this matter, but the data indicate with high confidence that the tidal prah of an open star cluster is asymmetrical with the corresponding confidence that Newtonian gravitation is falsified. Open star clusters depopulate more rapidly in Milgromian than in Newtonian dynamics and the COIN-Gaia13 cluster is here found to be nearly completely dissolved. In view of these results, the wide-binary star test and the Keplerian Galactic rotation curve finding are briefly discussed.

astro-ph.GA↗

arXiv2023

A simultaneous solution to the Hubble tension and observed bulk flow within 250 ${h^{-1}}$ Mpc

The $Λ$ cold dark matter ($Λ$CDM) standard cosmological model is in severe tension with several cosmological observations. Foremost is the Hubble tension, which exceeds $5σ$ confidence. Galaxy number counts show the Keenan-Barger-Cowie (KBC) supervoid, a significant underdensity out to 300~Mpc that cannot be reconciled with $Λ$CDM cosmology. Haslbauer et al. previously showed that a high local Hubble constant arises naturally due to gravitationally driven outflows from the observed KBC supervoid. The main prediction of this model is that peculiar velocities are typically much larger than expected in the $Λ$CDM framework. This agrees with the recent discovery by Watkins et al. that galaxies in the CosmicFlows-4 catalogue have significantly faster bulk flows than expected in the $Λ$CDM model on scales of $100-250 \, h^{-1}$~Mpc. The rising bulk flow curve is unexpected in standard cosmology, causing $4.8σ$ tension at $200 \, h^{-1}$~Mpc. In this work, we determine what the semi-analytic void model of Haslbauer et al. predicts for the bulk flows on these scales. We find qualitative agreement with the observations, especially if our vantage point is chosen to match the observed bulk flow on a scale of $50 \, h^{-1}$~Mpc. This represents a highly non-trivial success of a previously published model that was not constrained by bulk flow measurements, but which was shown to solve the Hubble tension and explain the KBC void consistently with the peculiar velocity of the Local Group. Our results suggest that several cosmological tensions can be simultaneously resolved if structure grows more efficiently than in the $Λ$CDM paradigm on scales of tens to hundreds of Mpc.

astro-ph.CO↗