arXiv subjects

H. A. Adarsha

Publications and source records attributed to H. A. Adarsha.

3 recordsLinked to original sources

arXiv2026

Transmutation Timescales for Dark Matter Induced Collapse of Compact Stars into Black Holes

Ultra-heavy asymmetric dark matter (DM) particles captured by compact stars can thermalize, self-gravitate, and collapse to form an endoparasitic black hole (EBH), whose subsequent growth may transmute the host star into a black hole. The continued existence of old millisecond pulsars (MSPs) and white dwarfs (WDs) thus places powerful constraints on the DM particle mass $m_χ$ and the DM-nucleon scattering cross-section $σ_{\rm nχ}$. We derive an analytical expression for the transmutation timescale by solving the EBH growth equation, consistently accounting for Bondi accretion of stellar matter, Hawking evaporation, and sustained DM feeding of the EBH in a steady-state capture regime. We also incorporate quantum effects in baryonic accretion when the hydrodynamic description breaks down, providing a unified treatment of EBH growth across both particle and fluid regimes. Adopting a physically transparent collapse criterion for fermionic and bosonic asymmetric DM, we compute EBH transmutation timescales for representative MSPs and WDs in environments with different DM densities. Although the physical ingredients are broadly similar to previous studies, this work derives updated constraints through a closed-form analytical treatment of EBH growth and an adopted prescription for the EBH formation timescale, yielding a lower critical EBH mass for sustained growth and revised transmutation timescales. Requiring the transmutation time to exceed $\sim 1$ Gyr for MSPs and $\sim 10$ Gyr for WDs, we derive revised constraints on $σ_{\rm nχ}$ over $m_χ\sim 10^{6}$--$10^{14}$ GeV, and show that EBHs with initial masses as small as $\sim 4\times10^{4}$ kg can undergo sustained growth, extending the region of DM parameter space probed by compact stars.

astro-ph.HE↗

arXiv2026

Magnetically arrested transmutation of a compact star

We introduce a novel mechanism -- Magnetically Arrested Transmutation (MAT) -- which could be a viable model to account for the observed over-representation of magnetic white dwarfs (WDs) near the Galactic centre (GC), and the presence of a magnetar as opposed to the absence of ordinary pulsars in the same region. In this scenario, compact stars accumulate asymmetric or non-self-annihilating dark matter particles, eventually forming an endoparasitic black hole (EBH) of initial mass $M_0$ at their core. Although such EBHs generally grow by accreting host matter, we show that sufficiently strong core magnetic fields can establish pressure equilibrium, thereby stalling further accretion and halting the star's transmutation into a black hole. We derive the conditions for this MAT to occur, identifying a critical parameter $β$, that encapsulates the interplay between the magnetic field strength, host matter density, and EBH mass. For $0 < β\leq 4/27$, the growth of the EBH is arrested, limiting its final mass ($M_{\rm f}$) to $M_0 4/27$, full transmutation may ensue. We argue that highly magnetized WDs may survive near the GC due to the MAT mechanism, as do high-spin ordinary WDs, despite hosting a central EBH. We also speculate a possibility that the magnetar PSR J1745-2900 survives near the GC due to the MAT mechanism. Overall, the MAT framework may explain an elevated population of magnetic WDs in dense dark matter environments, and hence could be tested and should have implications for understanding dark matter and compact objects.

astro-ph.HE↗

arXiv2025

Accretion inside astrophysical objects : Effects of rotation and viscosity

Sub-solar mass black holes could show up in gravitational wave observations in future and near-solar mass black holes might have been involved in the events GW190425 and GW190814. Since they cannot form from the stellar evolution, their creation requires exotic mechanisms. One such mechanism involves the capture of dark matter particles by stellar objects and their thermalization. When the criterion for the collapse of these dark matter particles is satisfied, a tiny endoparasitic black hole (EBH) forms and then it accretes matter from the host. The EBH may transmute the host into a black hole of nearly the same mass as the host or lesser, depending on the type of accretion. We examine this complex and poorly-explored accretion mechanism, considering the effects of rotation and viscosity but ignoring some other effects, such as those of pressure and magnetic field, as the first step. Using a general framework to assess the effects of rotation and viscosity on accretion, we show that the accretion could be stalled in some white dwarfs, but not in neutron stars. The stalled accretion should cause an opening in the host's polar regions, the extent of which depends on the mass and spin of the host.

astro-ph.HE↗