Dark Matter Signals from Black Hole Quasinormal Modes Suggest Parity Violation.

Research demonstrates that black holes possessing ‘axion hair’ exhibit parity violation – a breakdown in symmetry – within their electromagnetic signals. Numerical analysis of quasinormal modes, utilising Leaver’s method, reveals this effect, potentially offering a novel method for investigating the composition of dark matter and dark energy.

The universe’s most enigmatic objects, black holes, continue to yield subtle clues about fundamental physics. New research suggests that electromagnetic radiation emitted as black holes ‘ring down’ after a disturbance – known as quasinormal modes – may exhibit a violation of parity symmetry if these objects interact with hypothetical particles proposed to constitute dark matter and dark energy. This phenomenon, potentially detectable through polarisation measurements of emitted radiation, offers a novel avenue for investigating the composition of the dark sector. Sugumi Kanno, Jiro Soda, and Akira Taniguchi, from Kyushu and Kobe Universities in Japan, detail their investigation in the paper “Parity violation in photon quasinormal modes of black holes”, where they employ Leaver’s continued fraction method to model the behaviour of electromagnetic fields around black holes possessing ‘axion hair’ – a theoretical coupling to these dark matter candidates.

Black Hole Polarization as a Probe for Axion Dark Matter

The search for dark matter continues to drive innovation in both theoretical and observational physics. A recent study proposes a novel method for detecting axions – a leading dark matter candidate – by analysing the polarization of electromagnetic radiation emitted from black holes. This approach leverages the interaction between black holes, electromagnetic fields, and hypothetical axion fields, predicted by extensions to the Standard Model of particle physics.

Researchers model the coupling between electromagnetic and axion fields using the Chern-Simons interaction. This interaction, a specific term in theoretical field theories, generates a relationship between the two fields, influencing the behaviour of electromagnetic waves in the presence of an axion field. This coupling results in a set of equations describing both parity-even and parity-odd electromagnetic modes – modes differing in how their electric and magnetic fields transform under spatial inversion.

Numerical simulations are employed to model the propagation of electromagnetic waves around black holes immersed in axion fields. These simulations account for the complex curvature of spacetime around the black hole, as described by general relativity, and incorporate the effects of the Chern-Simons interaction. The simulations predict specific polarization signatures – patterns in the orientation of the electromagnetic wave’s electric field – that would arise from the presence of axions.

A key finding of the study is the demonstration of parity violation within the black hole’s quasinormal mode spectrum. Quasinormal modes are the characteristic ‘ringing’ frequencies at which a black hole vibrates after being disturbed. Parity violation signifies a preference for one polarization state over another, breaking the expected symmetry. Calculations reveal a distinct separation between the frequencies of the parity-even and parity-odd modes, providing a potential observational signature. This asymmetry arises from the interaction between the electromagnetic field and the ‘axion hair’ – a hypothetical field surrounding the black hole due to the presence of axions.

The implications of this research are significant for the exploration of the dark sector – the collective term for the universe’s unseen components, including dark matter and dark energy. By analysing the polarization of electromagnetic signals from black holes, astronomers may be able to detect the presence of axion fields and constrain their properties. This offers a complementary approach to direct detection experiments and searches for axions produced in the early universe.

Future observations with advanced telescopes and detectors will be crucial to test the predictions of this model. Refined theoretical modelling, combined with observational data, promises to deepen our understanding of axions and their role in the cosmos.