Black Hole Shadows Grow with Dark Matter and Cosmic Strings, Simulations Reveal

Scientists are increasingly focused on understanding the complex interplay between black holes and dark matter, and new research from Faizuddin Ahmed (The Assam Royal Global University), Ahmad Al-Badawi (Al-Hussein Bin Talal University), and İzzet Sakallı (Eastern Mediterranean University) et al. investigates observational signatures arising from a charged Bardeen black hole embedded within perfect fluid dark matter and coupled to a cloud of strings. Their work constructs a novel spacetime model, revealing how these combined factors influence the black hole’s horizon structure and crucially, its observable characteristics. This research is significant because it predicts measurable effects on the black hole shadow, quasiperiodic oscillations, and gravitational wave emissions, potentially offering independent constraints on both dark matter properties and the presence of string-like objects through future astronomical observations.

This work introduces a spacetime geometry combining a magnetic monopole charge from nonlinear electrodynamics, a logarithmic correction arising from the perfect fluid dark matter, and a parameter defining the cloud of strings, resulting in an asymptotically non-flat spacetime.

Analysis of the horizon structure reveals parameter ranges that yield non-extremal black holes, extremal configurations, and even the potential for naked singularities. Calculations of null geodesics, the photon sphere radius, and the black hole shadow demonstrate that both the cloud of strings and the perfect fluid dark matter contribute to an enlargement of the shadow size.
For neutral particle dynamics, researchers derived expressions for specific energy, angular momentum, and the location of the innermost stable circular orbit, providing insights into particle behaviour around this modified black hole. Examination of quasiperiodic oscillations through azimuthal, radial, and vertical epicyclic frequencies revealed a notable independence of the azimuthal frequency from the cloud of strings parameter.

Scalar field perturbations, governed by the Klein-Gordon equation, yielded an effective potential whose peak decreases with both the cloud of strings and perfect fluid dark matter parameters, although the transmission and reflection probabilities exhibit opposing responses to variations in these parameters. Semi-analytical methods were employed to obtain bounds on the greybody factor, further characterizing the black hole’s response to external perturbations.

The distinct effects of the cloud of strings parameter α and the perfect fluid dark matter parameter β on various observable quantities, including shadow measurements, QPO timing, and gravitational wave ringdown observations, could allow for independent constraints on these parameters. These findings suggest a pathway towards refining our understanding of dark matter and exotic astrophysical objects through multi-messenger astronomy.

Spacetime geometry, horizon properties and shadow characteristics of charged Bardeen black holes in modified gravity are investigated

A charged Bardeen black hole embedded within perfect fluid dark matter and coupled to a cloud of strings forms the basis of this research. The study constructs a spacetime geometry incorporating a magnetic monopole charge from nonlinear electrodynamics, a logarithmic correction arising from the perfect fluid dark matter, and a parameter representing the cloud of strings, resulting in a non-flat asymptotic spacetime.

Analysis of the horizon structure identified parameter ranges allowing for non-extremal black holes, extremal configurations, and the potential formation of naked singularities. Photon sphere radius and black hole shadow characteristics were then calculated, revealing that both the cloud of strings and the perfect fluid dark matter enlarge the shadow size.

Neutral particle dynamics were investigated by deriving the specific energy, angular momentum, and the location of the innermost stable circular orbit. Quasiperiodic oscillations were examined using azimuthal, radial, and vertical epicyclic frequencies, with a notable finding that the azimuthal frequency remains independent of the cloud of strings parameter.

Scalar field perturbations, governed by the Klein-Gordon equation, yielded an effective potential whose peak decreases with both parameters, while transmission and reflection probabilities exhibited opposite responses to variations in the cloud of strings and perfect fluid dark matter. Semi-analytical methods were employed to obtain greybody factor bounds, facilitating a detailed understanding of particle emission from the black hole. The distinct effects of the cloud of strings parameter and the perfect fluid dark matter intensity on these observables could enable independent constraints on these parameters through shadow measurements, QPO timing, and gravitational wave ringdown observations.

Horizon structure, shadow radius and particle dynamics in charged Bardeen black holes with dark matter and string clouds are thoroughly investigated

Researchers examined a charged Bardeen black hole surrounded by perfect fluid dark matter and a cloud of strings, constructing a metric function incorporating magnetic monopole charge, dark matter logarithmic correction, and the cloud of strings parameter. Analysis of the horizon structure identified parameter ranges allowing for non-extremal black holes, extremal configurations, and naked singularities.

Null geodesic calculations, sphere radius determinations, and shadow analysis revealed that both the cloud of strings and perfect fluid dark matter enlarge the black hole shadow. For neutral particle dynamics, the specific energy, angular momentum, and innermost stable circular orbit location were derived, providing detailed information about particle behaviour around the black hole.

Quasiperiodic oscillations were examined using azimuthal, radial, and vertical epicyclic frequencies, with a notable finding that the azimuthal frequency remains independent of the cloud of strings parameter. Scalar field perturbations, governed by the Klein-Gordon equation, yielded an effective potential whose peak decreases with both parameters, influencing the transmission and reflection of scalar fields.

The transmission and reflection probabilities exhibited opposing responses to variations in the cloud of strings and perfect fluid dark matter parameters. Semi-analytical methods were employed to obtain greybody factor bounds, quantifying the absorption and scattering of scalar fields by the black hole.

These results demonstrate that the distinct effects of α and β on various observables could allow independent constraints on these parameters through shadow measurements, QPO timing, and gravitational wave ringdown observations. This work suggests that combined observations may provide a means to independently constrain the parameters governing the black hole’s environment.

Charged Bardeen black hole horizons, shadow radii and test particle motion with dark matter and strings are investigated numerically

Researchers have modelled a charged Bardeen black hole incorporating both perfect fluid dark matter and a cloud of strings, revealing how these components influence the black hole’s structure and observable properties. The analysis constructs a metric function that combines the effects of a magnetic monopole charge, logarithmic corrections from the perfect fluid dark matter, and a parameter representing the cloud of strings, resulting in a spacetime that deviates from standard asymptotic flatness.

Investigations into the horizon structure delineate the conditions under which non-extremal black holes, extremal configurations, and even naked singularities can form. Detailed calculations of null geodesics, the photon sphere radius, and the black hole shadow demonstrate that both the cloud of strings and the perfect fluid dark matter contribute to an enlargement of the shadow size.

Furthermore, the study examines the dynamics of neutral test particles, determining the specific energy, angular momentum, and the location of the innermost stable circular orbit, alongside an analysis of quasi-periodic oscillations through epicyclic frequencies, notably, the azimuthal frequency remains unaffected by the cloud of strings parameter. Scalar field perturbations, assessed via the Klein-Gordon equation, show a decreasing peak in the effective potential with both parameters, though transmission and reflection probabilities exhibit opposing responses to variations in the cloud of strings and perfect fluid dark matter.

The authors acknowledge limitations in the semi-analytical methods used to determine greybody factors, which may introduce approximations in the results. Future research could focus on refining these methods or exploring the implications of the findings for gravitational wave astronomy, specifically examining how the distinct effects of the perfect fluid dark matter and cloud of strings on observables like shadow measurements, quasi-periodic oscillation timing, and gravitational wave ringdown could allow for independent constraints on their respective parameters. These results establish a pathway toward utilising observational data to better understand the complex interplay between black holes and their surrounding astrophysical environments.