G objects as Primordial Black Hole-Neutron Star Remnants: Population Modeling and Multi-Wavelength Observables

Abstract

The nature of the so-called G objects orbiting the Galactic Center remains unresolved. These sources exhibit compact Br$γ$ emission, extreme infrared colors, and remarkable dynamical stability through close passages to the central supermassive black hole, challenging conventional interpretations as stars or unbound gas clouds. We investigate the hypothesis that G objects are the remnants of neutron stars that have been converted into low-mass black holes through the capture of primordial black holes, a viable dark-matter candidate. We construct a population-level framework linking the abundance and spatial distribution of these remnants to the neutron-star population, the inner dark-matter density profile, and the primordial black-hole mass and abundance. Within this framework, the observed G-object population and the long-standing deficit of ordinary radio pulsars in the Galactic Center emerge as complementary consequences of the same conversion process. We further identify a suite of observational signatures-across infrared, radio, X-ray, and microlensing channels-that render this scenario empirically testable and distinguishable from stellar-envelope models. Our results show that G objects can act as sensitive probes of compact-object capture physics and of dark matter on sub-galactic scales.

Figures (19)

• Figure 1: Timescales for PBH-neutron star conversions for $\alpha = 2$, $f_{\rm DM} =1$.
• Figure 2: Cumulative neutron-star count predicted by a pulsar-calibrated 4 component Galactic model, normalized to a total neutron-star population $N_{\rm NS,tot}\sim10^{8}$.
• Figure 3: The number of converted G objects within a spherical radius $r$ for the allowable region of $\alpha, \gamma$ , $M_{\text{PBH}}= 10^{-9}$ and $f_{\text{DM}} =1.$
• Figure 4: Radial dependence of the pulsar conversion fraction $\Upsilon_{\rm psr}(r) = 1 - \exp[-t_{\rm psr}/\langle t_{\rm con}(r)\rangle]$ for a representative PBH mass $M_{\rm PBH}=10^{-12}\,M_\odot$ and maximal dark-matter fraction $f_{\rm DM}=1$. Different curves correspond to varying inner dark-matter slopes $\alpha$.
• Figure 5: Radial dependence of the pulsar conversion fraction $\Upsilon_{\rm psr}(r) = 1 - \exp[-t_{\rm psr}/\langle t_{\rm con}(r)\rangle]$ for a representative PBH mass $M_{\rm PBH}=10^{-12}\,M_\odot$ and maximal dark-matter fraction $f_{\rm DM}=1$. Different curves correspond to varying inner dark-matter slopes $\alpha$.