Astrophysical Black holes: An Explanation for the Galaxy Quenching

In light of increasing observational evidence supporting the existence of ultra-compact objects, we adopt the term astrophysical black hole to refer to any object having a huge mass confined within a sufficiently small region of spacetime. This terminology encompasses both the classical black hole solutions predicted by general relativity, as well as alternative compact objects that may not possess an event horizon. We propose models of Astrophysical Black holes (ABHs) without event horizons (EHs), as a more viable explanation for the long-term quenching phenomenon in galaxies. At the same time, the short-term quenching is explained here in terms of an efficient feedback expected in the models of stellar-mass astrophysical black holes (StMABHs). We have calculated the radiative flux from the disk in a general spherically symmetric metric background and used it to contrast the distinctive features of the BHs and ABHs scenarios. We demonstrate the relative ease of wind generation from the accretion disk surrounding an ABH without an event horizon, compared to a BH, and highlight the significant strength of these winds. The nature of the feedbacks arising from accretion onto a BH and an ABH in the quasar' and radio’ modes are compared and some possible observational signatures of the StMABHs are pointed out.

💡 Research Summary

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The paper proposes a novel framework for explaining both long‑term and short‑term galaxy quenching by invoking “astrophysical black holes” (ABHs) that lack an event horizon. The authors argue that the conventional picture—where supermassive black holes (SMBHs) with event horizons regulate star formation through AGN feedback—is insufficient to account for recent JWST observations of massive quiescent galaxies at redshifts > 4 and even a mini‑quenched galaxy at z ≈ 7. In the standard black‑hole scenario, the accretion disk is truncated at the innermost stable circular orbit (ISCO), limiting the maximum radiative flux and the power that can be transferred to galactic‑scale winds.

To overcome this limitation, the authors introduce two classes of horizon‑less compact objects. The first, a massive ABH, is an ultra‑compact, high‑density object whose spacetime does not contain a trapped surface. Because there is no event horizon, the accretion disk can extend all the way to the central singularity. Using a general spherically symmetric metric, they derive the radiative flux from the disk (a generalized Novikov‑Thorne expression) and show that (\mathcal{F}(r)) diverges as (r\to0). Consequently, the disk temperature and pressure become extremely high, driving powerful thermal and magnetically‑accelerated winds. Their semi‑analytic calculations indicate that the mass‑loss rate in winds can be an order of magnitude larger than in the horizon‑bounded case, with wind velocities reaching 0.1–0.3 c. Such winds can continuously heat the circum‑galactic medium, prevent cooling flows, and thus maintain a long‑lasting quenching of star formation.

The second class, stellar‑mass astrophysical black holes (StMABHs), represents the transient phase of a collapsing massive star before an event horizon fully forms. During this brief interval (seconds to minutes), the core becomes an ultra‑dense, horizon‑free region capable of emitting a burst of ultra‑high‑energy particles. The authors argue that this burst can produce a rapid, localized depletion or heating of the interstellar medium, leading to a short‑term, “mini‑quenching” episode. This mechanism offers a natural explanation for the JWST‑identified mini‑quenched galaxy at z ≈ 7, whose stellar mass (~10⁸ M⊙) suggests that only a modest central engine could have caused the observed rapid shutdown of star formation.

Beyond the theoretical modeling, the paper discusses observational diagnostics that could distinguish horizon‑less ABHs from conventional black holes. These include: (i) shadow imaging—ABHs may produce a full‑moon‑like brightness distribution rather than a dark silhouette; (ii) orbital precession—both positive and negative perihelion shifts can occur near naked singularities; (iii) Lense‑Thirring precession and pulsar timing—distinct signatures in gyroscope or pulsar signal delays; and (iv) tidal‑force measurements. The authors note that current facilities such as the Event Horizon Telescope, NICER, and upcoming gravitational‑wave detectors could probe these effects.

In summary, the paper argues that horizon‑less ultra‑compact objects provide a more efficient feedback channel than traditional SMBH‑AGN models. Massive ABHs can sustain powerful, long‑duration winds that keep galactic halos hot and star formation suppressed over gigayear timescales, while StMABHs can trigger brief, intense quenching events in low‑mass, early‑epoch galaxies. By integrating these two mechanisms, the authors present a unified explanation for the diverse quenching phenomena now emerging from JWST and other surveys, and they outline concrete observational strategies to test the existence of such “naked‑singularity” black‑hole mimics.