Dancing with invisible partners: Three-body exchanges with primordial black holes

Abstract: The abundance of massive primordial black holes has historically been constrained by dynamical probes. Since these objects can participate in hard few-body scattering processes, they can readily transfer energy to stellar systems, and, in particular, can disrupt wide binaries. However, disruption is not the only possible outcome of such few-body processes. Primordial black holes could also participate in exchange processes, in which one component of a binary system is ejected and replaced by the black hole itself. In this case, the remaining object in the binary would dynamically appear to have an invisible companion. We study the rate of exchange processes for primordial black holes as a component of dark matter and evaluate possible mechanisms for detecting such binaries. We find that many such binaries plausibly exist in the Solar neighborhood, and show that this process can account for observed binary systems whose properties run counter to the predictions of isolated binary evolution.

• The paper demonstrates that a primordial black hole can replace a binary companion through a distinct three-body exchange process.
• The analysis reveals that the exchange rate peaks when the PBH mass is comparable to the ejected object's mass, despite overall rarity.
• The findings suggest potential observational signatures that could redefine our understanding of binary formation channels in astrophysics.

Overview of "Dancing with invisible partners: Three-body exchanges with primordial black holes"

The paper presented explores a novel dynamical interaction involving primordial black holes (PBHs) and binary systems: the three-body exchange process. Historically, PBHs have been recognized as significant players in the disruption and softening of binary systems. This study, however, primarily investigates the plausibility and implications of a PBH replacing one component of a binary system, leading to what is termed an "invisible partner" scenario.

Three-Body Exchanges with PBHs

The dynamical processes involving three bodies can result in several outcomes, as categorized by previous seminal works. Most relevant to this research is the exchange process, in which a PBH can eject one component of a binary and assume its place, forming a new binary system. This phenomenon, distinct from mere softening or disruption, results in one of the visible binary partners seemingly interacting with an unseen companion. The authors provide a detailed analytical framework based on established models of three-body interactions, estimating the probability and rate of such exchanges in various astrophysical environments.

Numerical Analysis and Results

The analysis demonstrates that the exchange rate is maximized when the mass of the PBH is comparable to the mass of the ejected object from the binary. This finding is consequential, as it suggests that PBHs in certain mass ranges could have non-negligible dynamical interactions with stellar binaries, asteroid binaries, and possibly exoplanetary systems within the Milky Way. However, typical exchange rates per binary are notably low, suggesting that although exchange events are rare on cosmic timescales, the vast quantity of binary systems in our galaxy allows for a reasonable chance of their occurrence.

Implications for Observations and Astrophysics

A striking implication of the study is the subtlety of detecting such exchanges. Binaries that exhibit dynamical properties inconsistent with standard astrophysical formation models could potentially indicate the presence of a PBH. The authors suggest Gaia-observed binaries with black hole components, which defy common evolutionary scenarios, might be explained by these exchange processes. Such findings prompt a reevaluation of binary black hole formation channels and present a novel potential method to detect and characterize the PBH population.

Future Prospects and Theoretical Speculations

The existence of PBHs has gained interest due to their potential role in solving the dark matter problem. This paper adds another layer by suggesting that PBH exchanges might enrich our understanding of binary system dynamics and offer indirect evidence for the PBH hypothesis. Future research should focus on high-precision astrometric missions capable of distinguishing these invisible partnerships. Moreover, the increasing accuracy of stellar evolution models could aid in effectively ruling out or confirming primordial origins for binary black hole companions, thereby refining our understanding of the non-visible mass components of the universe.

In conclusion, while exchanges involving PBHs are statistically rare, they present a compelling case for being significant in specific astrophysical contexts. The research underlines the intricate interplay involved in three-body gravitational dynamics, encouraging further theoretical exploration and observational endeavors that could probe the veiled corridors of our galactic neighborhood where invisible partners might dance.