The Potential Impact of Primordial Black Holes on Exoplanet Systems

TL;DR

This work assesses whether a Galactic population of primordial black holes (PBH) can perturb exoplanetary orbits via close flybys, complementing stellar perturbations. The authors integrate galactic-scale PBH incidence with detailed N-body flyby simulations, using Gala to estimate encounter rates and REBOUND to map resulting changes in orbital elements, notably $e$ and $a$. They find that even a sub-percent PBH fraction, e.g. $f_{PBH}\sim10^{-7}$ with $M_{PBH}\sim0.1\,M_\odot$, can induce measurable perturbations to Jupiter- and Neptune-like planets, including $\Delta e\sim10^{-2}$ and possible $e_f>1$ for very close hits, potentially contributing to planet ejection. While current exoplanet data alone cannot place strong constraints, the framework shows how precision orbital demographics could, in the future, constrain PBH populations and highlights clean, single-planet systems as favorable laboratories for such dynamical tests.

Abstract

The orbits of planetary systems can be deformed from their initial configurations due to close encounters with larger astrophysical bodies. Typical candidates for close encounters are stars and binaries. We explore the prospect that if there is a sizeable population of primordial black holes (PBH) in our galaxy, then these may also impact the orbits of exoplanets. Specifically, in a simplified setting, we study numerically how many planetary systems might have a close encounter with a PBH, and analyze the potential changes to the orbital parameters of systems that undergo PBH flybys.

Figures (9)

• Figure 1: Plot made through "exoplanets.eu" with the selection "mass:mjup $>$ 0.1 AND "confirmed" in planet$\_$status".
• Figure 2: For illustrative purposes only we show here the case of four planets on circular orbits around a central star ($\star$), whereas in our main simulations we only consider single planets orbiting stars. The flyby of the intruding body lies on hyperbolic trajectories, as shown as brown, black and yellow curves. Coloured dots show the point of closest approach between certain pairs.
• Figure 3: Flow diagram of the computations used to study how primordial black holes (PBHs) may impact exoplanet orbits.
• Figure 4: Results of Gala simulations. The star is assumed to have a circular orbit around the galactic center at a distance $d$; we consider $d=$2,3,4, and 5 kpc. The left panel shows the average number of close encounters as a function of the distance of the planet-star system from the galactic centre. The centre and right panels show histograms of the distance between the star and the intruder, and their relative velocities. The histograms show combined results for an equal number of runs at each value of $d$.
• Figure 5: The probability that a PBH enters a given closest approach distance $\alpha$ from an initial distance $d$. For star-Jupiter (star-Neptune) systems we take $\alpha=15$ AU (90 AU).