The Missing Isolated Black Holes and the Hypothetical “Elonoids”

A Study of Expected Populations, Accretion Emissions, and Interstellar Void Formation – or “Dark Gothic Black Holes”

Abstract:

Observations indicate that the nearest known black hole is located over 1,000 light‐years away, despite stellar population models predicting a far higher number of isolated stellar‐mass black holes (BHs) in our galactic neighborhood. In this article we (i) estimate the expected number and mass range of massive objects in our local region of the Galaxy, (ii) assess the fraction that may be devoid of any accretion disk (i.e., “naked” BHs), (iii) calculate the omnidirectional Bondi–Hoyle accretion of interstellar gas into these BHs and the associated multiwavelength emissions, and (iv) show that given current sensitivity limits, such objects should be observable within a few hundred light‐years. We then propose a hypothetical solution—“Elonoids”: small, cold, and empty “bubbles” devoid of any substance, created over millions of years by the slow clearing of the interstellar medium (ISM) surrounding isolated BHs. These Elonoids may help explain the “missing BH” problem.

1. Introduction

Theoretical estimates suggest that the Milky Way hosts on the order of 10^8 stellar‐mass black holes, roughly one per 1,000 stars. In the solar neighborhood, naive statistical arguments imply that an isolated BH should be found within ∼30 light‐years. Yet the nearest confirmed black hole (Gaia BH1) lies at ≈1,560 light‐years. Most known BHs are identified as X‑ray binaries or via their astrometric influence on a companion star, while a majority of isolated BHs (hereafter “naked” BHs) remain undetected due to their low intrinsic luminosity. This paper presents a series of calculations exploring the expected Bondi accretion of ambient ISM onto such BHs, the resulting emissions, and the apparent detection rate. We then propose that many isolated BHs may, over millions of years, “clear” their surroundings by slowly accreting gas and generating weak outflows, thereby forming localized, cold, low-density regions in the ISM—termed here “Elonoids.”

2. Expected Population and Characteristics of Isolated Black Holes

2.1. Number Density and Mass Range

Assuming a typical Milky Way stellar population of ∼10^11 stars and a BH formation efficiency of ∼10^–3, the total number of BHs in our Galaxy is estimated as:

If stars in the solar neighborhood number ∼0.1 stars per cubic parsec, then the local density of BHs should be roughly:

The expected mean separation, $d$ , is then given by:

Observationally, however, the closest confirmed BH is over 1,000 light‐years away, suggesting that the majority of isolated BHs are “dark” and escape detection.

The mass range of stellar‐mass BHs is thought to lie between ∼3–20 $M⊙M_\odot$ (with most clustering around 5–10 $M⊙M_\odot$ ).

2.2. Fraction Devoid of Accretion Disks

Most isolated BHs lack a binary companion or significant accretion disk. Thus, it is plausible that nearly 100% of these BHs are “naked” in the sense that they are not actively accreting at high rates from a companion star. Their only accretion is from the ambient ISM, which is orders of magnitude weaker than accretion in X‑ray binaries.

3. Interstellar Gas Inflow and Bondi–Hoyle Accretion

This luminosity, though extremely low compared to active X‑ray binaries, would primarily emerge in the X‑ray and infrared wavelengths.

4. Predicted Observational Signatures

4.1. Expected Flux and Detection Range

At a distance $d$ , the observed flux is:

4.2. The Missing Black Hole Problem

Despite theoretical expectations, the nearest known BH (Gaia BH1) is located at ≈1,560 light‐years. The absence of nearby detections suggests either:

Our detection methods are biased toward systems with accretion disks or companions.
The majority of isolated BHs are cloaked in a manner that suppresses observable emissions.

5. Hypothetical Resolution: “Elonoids”

We postulate that many isolated BHs, as they slowly accrete the ISM, may create localized, cold, and empty bubbles in the ISM over millions of years. We term these bubbles “Elonoids”. Characteristics include:

Dynamics:
As the BH and its associated Elonoid travel through the Galaxy, they intermittently encounter denser ISM regions. During these encounters—termed the “brooming phase”—the BH may briefly accrete additional material, temporarily increasing its luminosity. However, for the majority of their lifetimes, these objects remain in a “quiescent” state.
Observational Implications:
If a small fraction (∼1%) of isolated BHs are in the brooming phase at any given time, then transient X‑ray or infrared flares might be observed. Additionally, radio observations could reveal small HI voids corresponding to these Elonoids.

6. Conclusions

Our calculations predict that:

Expected local density: An isolated stellar‐mass BH should be found within ∼30 light‐years, yet the nearest observed BH is over 1,000 light‐years away.
Bondi accretion: A 10 solar mass BH in the ISM accretes at with a corresponding luminosity
Detectability: With current X‑ray and IR sensitivities, many such BHs should be detectable out to hundreds of light‐years.
Elonoids hypothesis: The absence of detectable isolated BHs may be due to the formation of “Elonoids” — localized supervacuum bubbles created as BHs clear the ISM around them over millions of years. These bubbles remain cold, lonely, naked and largely empty, suppressing accretion emissions except during brief brooming phases.

The Elonoid model thus provides a possible resolution to the missing BH problem and motivates further observational campaigns (e.g., via radio HI surveys, deep X‑ray studies, and astrometric microlensing searches) to uncover these elusive objects.

8. Future Work

Future observational campaigns and numerical simulations are essential to test the Elonoid hypothesis. If such supervacuum bubbles exist, they may provide the key to resolving the long-standing discrepancy between the predicted and observed populations of isolated black holes.

9. About the author

The author of this hypothesis is not a professional astrophysicist, nor affiliated with any academic institution. This work was developed in an informal, independent capacity, primarily between late-night doomscrolling sessions and moments of existential contemplation. While the calculations follow established physical principles and are presented in a structured scientific format, they should be considered a speculative thought experiment rather than a rigorously peer-reviewed study.

The author welcomes constructive feedback, brutal critiques, and any professional astrophysicists who may wish to either debunk this outright or refine it into something useful. Until then, the Elonoids Hypothesis remains an exercise in creative scientific speculation and an example of how even an unemployed nobody with limited formal training can still engage in meaningful theoretical exploration, given access to ChatGPT.

9. About the naming convention

I fully welcome alternative names for this phenomenon. However, I must admit that it was late at night, I was running on questionable amounts of caffeine, and I needed something catchy to describe cold, lonely, detached objects that create voids devoid of any meaningful substance, wander aimlessly through space, and are best avoided close-up. The name Elonoids just sort of… happened.

I recognize that this is not the most academic-sounding term, and I humbly invite better suggestions from the more serious minds in astrophysics.

Please, for the love of all things scientific, do not tell Sabine Hossenfelder. I am fragile. I cannot handle the level of merciless Germanic skepticism she would unleash upon me. I just want to have my little thought experiment without getting verbally atomized.

If this idea ever makes it into actual scientific discourse, I promise to rename it to something appropriately Greek, Latin, or ominously mysterious-sounding. Lethoids? Voidons? Hadons? Until then, please indulge my late-night sci-fi instincts and let me have my Elonoids moment.