The Life and Death of Stars That Capture Primordial Black Holes

summary

Video file (mp4)

The gist

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In short

This research models how stars capture primordial black holes (PBHs) and what happens next. By combining stellar evolution and simulations, the study predicts two main outcomes: either an explosive disruption of the star due to a forming disk or a quiet consumption of the star by the black hole. This framework helps determine if captured PBHs can leave behind observable transients or specific types of compact remnants like high-spin black holes.

Key concepts

Capture Dynamics
PBH capture is driven by three-body interactions, often involving a companion planet or star. For a solar-type star, capturing a light PBH requires very tight orbits for the companion to ensure the black hole spirals in during the main sequence lifetime.
Disk Formation Threshold
A disk forms when gas accretion has enough specific angular momentum to circularize outside the black hole's innermost stable orbit. This critical threshold depends on how fast the host star rotates and how long it has been captured, determining if a violent explosion or quiet consumption occurs.
Explosive Disruption Branch
This outcome happens when the mass of the forming accretion disk is greater than the star's total mass. This leads to powerful feedback, including jets and winds, that disrupt the star rapidly, potentially producing bright transient signals like X-ray flashes or gamma-ray bursts.
Quiet Death Branch
If disk formation is delayed or the black hole grows slowly enough to consume the star before a massive disk forms, the system enters this branch. The black hole consumes the star relatively peacefully, leaving behind a remnant whose mass is comparable to what was originally in the star.

Terminology used across episodes

This episode discusses

The paper

The Life and Death of Stars That Capture Primordial Black Holes · Read on arXiv

Massachusetts Institute of Technology · Flatiron Institute · Princeton University · New York University Department of Physics and Center for Cosmology and Particle Physics, New York University Department of Physics and Center for Computational Astrophysics, Flatiron Institute, Princeton University Department of Astrophysical Sciences, Princeton University Leinweber Institute for Theoretical Physics, Stanford University

Primordial black holes (PBHs) in the asteroid mass window (10 17-10 23, g) remain viable dark matter candidates and can be captured by stars. We develop the first global framework for the evolution of stars that capture PBHs, combining analytic calculations, stellar evolution models, 3D general-relativistic magnetohydrodynamic simulations, and Monte Carlo population synthesis. We find that the fate of these systems bifurcates: PBHs that form an accretion disk before consuming the host drive explosive disruption, whereas PBHs captured too late or growing too slowly consume the star quietly. Capture is dominated by three-body interactions with planetary or stellar companions. For a solar-type host with a Jupiter analog, inspiral within a main-sequence lifetime requires M BH crit 10 22, g, while lighter PBHs generally require tighter companions. Once deposited at the center, the PBH grows through inefficient quasi-spherical Bondi accretion; if it reaches the angular-momentum threshold before consuming the host, the inflow circularizes into a disk. Our Monte Carlo calculations yield sizable quiet-consumption and explosive-disruption populations, with final PBH masses M BH about0.01-1,M and disk-forming PBH spins a about0.8. Disk formation is the point of no return: disk winds and relativistic jets of about10 45-10 50, erg,s-1 disrupt the star within minutes. The resulting transients may include a about day-long UV/blue signal, radio afterglow, and, if the jet escapes, an X-ray-flash/low-luminosity gamma-ray-burst (XRF/llGRB) signal. For an O(1) PBH dark matter fraction and optimistic capture assumptions, the event rate can reach that of llGRBs. The low-mass, high-spin remnants offer a complementary PBH probe and possible source for subsolar BH mergers.

Transcript

Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: We're looking at the paper: "The Life and Death of Stars That Capture Primordial Black Holes".

Jocelyn: Here's the gist of the paper. The second text appears to be a placeholder or a failed extraction attempt, indicating that it only contained a list of references and no substantive summary.

Vera: Therefore, I will synthesize the comprehensive information from the first text to create a long and detailed summary as requested.

Jocelyn: Detailed Research Summary: The Life and Death of Stars That Capture Primordial Black Holes This research presents a global framework designed to model the evolution of stars that have captured primordial black holes (PBHs) within the asteroid mass window (10 17 – 10 23 g), which are considered viable dark matter candidates.

Vera: The study integrates a multi-faceted approach, combining analytic calculations, stellar evolution models (such as MESA), sophisticated 3D general-relativistic magnetohydrodynamic (GRMHD) simulations, and Monte Carlo population synthesis to map the complex evolutionary pathways of these captured systems.

Title and authors: Vera: Now we're talking about how this paper sets up its investigation into "The Life and Death of Stars That Capture Primordial Black Holes" and who is behind this research.

Jocelyn: The authors are Ottlieb, Cantiello, Norton, Van Tilburg, and Kleban. They are tackling a problem where the mass window for these primordial black holes spans from asteroid masses up to sublunar masses around ten to twenty-three grams.

Subrahmanyan: That broad mass range is crucial because it’s where existing constraints on primordial black holes are weakest, meaning they could still be a significant fraction of dark matter in our galaxy.

Vera: Right, and the main point here is that stars offer a way to study these objects in a dense environment, which is something you can't really do in more diffuse regions.

Jocelyn: The paper argues that if primordial black holes are common enough, they would have frequent close encounters with stars, making capture by stellar systems actually plausible.

Subrahmanyan: If they are captured and migrate to the core, the way a black hole influences its host star’s evolution is fundamentally different compared to just having a diffuse environment around it.

Vera: That migration leads to what they call a "Hawking star," which is essentially a natural laboratory for studying how black holes grow in dense, rotating media.

The paper's summary: Jocelyn: So, the paper summarizes their approach by tracking the PBH through several key stages: capture, growth via Bondi accretion at the stellar core, disk formation, and finally determining whether it explodes or dies quietly.

Vera: They focus heavily on that transition point where a rotating accretion disk forms when the gas's specific angular momentum hits a certain threshold required for circularization outside of the black hole's innermost stable circular orbit.

Subrahmanyan: That threshold is very dependent on how fast the host star is spinning and how long it’s been around since the capture event, which makes things quite complex.

Jocelyn: The paper splits the fate determination into two main branches based on whether that disk formation happens before the black hole finishes consuming its host star.

Vera: If a disk forms and its mass is greater than the available stellar mass, you get this explosive disruption driven by powerful feedback mechanisms like disk winds and relativistic jets.

Subrahmanyan: That explosive branch can lead to transient signals like a day-long UV/blue signal, a radio afterglow, and potentially an X-ray flash or low-luminosity gamma-ray burst if the jet manages to escape.

Jocelyn: Conversely, if the disk formation threshold is higher than what's available in the star, the black hole just consumes it quietly before any big disk can form.

The paper's improvements: Vera: The authors suggest several ways this framework improves on previous work by combining analytic calculations with sophisticated stellar evolution models like MESA and three dee general-relativistic magnetohydrodynamic simulations <ref:2606.02700#pg1,3D general-relativistic magnetohydrodynamic simulations>.

Jocelyn: They use Monte Carlo population synthesis to map out these complex evolutionary pathways, which helps them generate a more realistic view of the possible outcomes.

Subrahmanyan: A specific improvement they highlight is deriving a novel lower bound on the PBH mass for this combined capture-and-inspiral process to complete within a main-sequence lifetime, which tightens constraints on the intermediate mass window.

Vera: They also provide a key analytic expression relating disk formation parameters, specifically Equation thirty-three which shows how the disk mass relates to the host star's properties and rotational history.

Jocelyn: This equation helps us quantify exactly when that point of no return happens, by comparing the specific angular momentum of gas at the Bondi radius against what is needed for circularization outside the ISCO.

Conclusion: Vera: So, wrapping up this discussion on "The Life and Death of Stars That Capture Primordial Black Holes," the paper shows that both quiet and explosive deaths can account for sizable fractions of the delivered Hawking-star population.

Jocelyn: The relative importance between those two branches depends entirely on the system parameters, like how fast the star is spinning and how much mass is available in that accretion disk.

Subrahmanyan: From a cosmological view, this means understanding these outcomes helps us constrain the PBH abundance by focusing on capture rates and binary survival dynamics.

Vera: The paper concludes that figuring out these specific outcomes requires detailed modeling of magnetic flux generation and how those jets or winds propagate through the stellar envelope.

Jocelyn: We're directed toward future research focusing on constraining the PBH abundance by looking closely at capture rates, binary survival dynamics, and the observational selection effects.

Subrahmanyan: Ultimately, this work provides a clearer picture of how these captured objects interact with baryonic matter in dense stellar systems.

Vera: That covers what this study has to say for now on "The Life and Death of Stars That Capture Primordial Black Holes."

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