Imaging fermionic dark matter cores at the center of galaxies

TL;DR

This paper explores whether dense fermionic dark matter cores at galactic centers can produce images similar to black holes, potentially mimicking their observational signatures but lacking photon rings, thus offering an alternative explanation within general relativity.

Contribution

It demonstrates that fermionic dark matter cores can produce black hole-like images and spectra, providing a novel alternative to black holes in galactic centers within the current dark matter framework.

Findings

Fermionic dark matter cores can mimic black hole images with central brightness depressions.

Dark matter cores lack photon rings, unlike black holes, aiding observational discrimination.

Simulated images show features consistent with current VLBI observations of galactic centers.

Abstract

Current images of the supermassive black hole (SMBH) candidates at the center of our Galaxy and M87 have opened an unprecedented era for studying strong gravity and the nature of relativistic sources. Very-long-baseline interferometry (VLBI) data show images consistent with a central SMBH within General Relativity (GR). However, it is essential to consider whether other well-motivated dark compact objects within GR could produce similar images. Recent studies have shown that dark matter (DM) halos modeled as self-gravitating systems of neutral fermions can harbor very dense fermionic cores at their centers, which can mimic the spacetime features of a black hole (BH). Such dense, horizonless DM cores can satisfy the observational constraints: they can be supermassive and compact and lack a hard surface. We investigate whether such cores can produce similar observational signatures to those of BHs when illuminated by an accretion disk. We compute images and spectra of the fermion cores with a general-relativistic ray tracing technique, assuming the radiation originates from standard $\alpha$ disks, which are self-consistently solved within the current DM framework. Our simulated images possess a central brightness depression surrounded by a ring-like feature, resembling what is expected in the BH scenario. For Milky Way-like halos, the central brightness depressions have diameters down to $\sim 35\, \mu$as as measured from a distance of approximately $8\,$kpc. Finally, we show that the DM cores do not possess photon rings, a key difference from the BH paradigm, which could help discriminate between the models.