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Eccentricity Evolution in Gaseous Dynamical Friction
Earth and Planetary Astrophysics · Submitted 2 Mar 2022
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim More broadly, our findings indicate that binary systems may routinely emerge from common envelope phases with non-zero eccentricities that were excited by the dynamical friction forces that drove their orbital tightening.
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The abstract, sentence by sentence
We analyse how drag forces modify the orbits of objects moving through extended gaseous distributions. We consider how hydrodynamic (surface area) drag forces and dynamical friction (gravitational) drag forces drive the evolution of orbital eccentricity. While hydrodynamic drag forces cause eccentric orbits to become more circular, dynamical friction drag can cause orbits to become more eccentric. We develop a semi-analytic model that accurately predicts these changes by comparing the total work and torque applied to the orbit at periapse and apoapse. We use a toy model of a radial power-law density profile, $\rho \propto r^{-\gamma}$, to determine that there is a critical $\gamma = 3$ power index which separates the eccentricity evolution in dynamical friction: orbits become more eccentric for $\gamma < 3$ and circularize for $\gamma > 3$. We apply these findings to the infall of a Jupiter-like planet into the envelope of its host star. The hydrostatic envelopes of stars are defined by steep density gradients near the limb and shallower gradients in the interior. Under the influence of gaseous dynamical friction, an infalling object's orbit will first decrease in eccentricity, then increase. The critical separation that delineates these regimes is predicted by the local density slope and is linearly dependent on polytropic index. More broadly, our findings indicate that binary systems may routinely emerge from common envelope phases with non-zero eccentricities that were excited by the dynamical friction forces that drove their orbital tightening.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We analyse how drag forces modify the orbits of objects moving through extended gaseous distributions. | contribution 0.67 | 0.87 | 0.03 | asserted 0.80 |
| s1 | We consider how hydrodynamic (surface area) drag forces and dynamical friction (gravitational) drag forces drive the evolution of orbital eccentricity. | contribution 0.83 | 0.71 | 0.08 | asserted 0.68 |
| s2 | While hydrodynamic drag forces cause eccentric orbits to become more circular, dynamical friction drag can cause orbits to become more eccentric. | result 0.95 | 0.64 | 0.29 | asserted 0.62 |
| s3 | We develop a semi-analytic model that accurately predicts these changes by comparing the total work and torque applied to the orbit at periapse and apoapse. | method 0.93 | 0.96 | 0.08 | asserted 1.00 |
| s4 | We use a toy model of a radial power-law density profile, $\rho \propto r^{-\gamma}$, to determine that there is a critical $\gamma = 3$ power index which separates the eccentricity evolution in dynamical friction: orbits become more eccentric for $\gamma < 3$ and circularize for $\gamma > 3$. | result 0.96 | 0.95 | 0.30 | asserted 1.00 |
| s5 | We apply these findings to the infall of a Jupiter-like planet into the envelope of its host star. | contribution 0.79 | 0.84 | 0.04 | asserted 0.87 |
| s6 | The hydrostatic envelopes of stars are defined by steep density gradients near the limb and shallower gradients in the interior. | background 1.00 | 0.08 | 0.02 | asserted 1.00 |
| s7 | Under the influence of gaseous dynamical friction, an infalling object's orbit will first decrease in eccentricity, then increase. | result 0.98 | 0.85 | 0.21 | asserted 0.98 |
| s8 | The critical separation that delineates these regimes is predicted by the local density slope and is linearly dependent on polytropic index. | result 0.98 | 0.84 | 0.14 | asserted 0.99 |
| s9 | More broadly, our findings indicate that binary systems may routinely emerge from common envelope phases with non-zero eccentricities that were excited by the dynamical friction forces that drove their orbital tightening. | interpretation 1.00 | 0.78 | 0.55 | hedged possibility 1.00 |
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The paper
Original abstract
We analyse how drag forces modify the orbits of objects moving through extended gaseous distributions. We consider how hydrodynamic (surface area) drag forces and dynamical friction (gravitational) drag forces drive the evolution of orbital eccentricity. While hydrodynamic drag forces cause eccentric orbits to become more circular, dynamical friction drag can cause orbits to become more eccentric. We develop a semi-analytic model that accurately predicts these changes by comparing the total work and torque applied to the orbit at periapse and apoapse. We use a toy model of a radial power-law density profile, $\rho \propto r^{-\gamma}$, to determine that there is a critical $\gamma = 3$ power index which separates the eccentricity evolution in dynamical friction: orbits become more eccentric for $\gamma < 3$ and circularize for $\gamma > 3$. We apply these findings to the infall of a Jupiter-like planet into the envelope of its host star. The hydrostatic envelopes of stars are defined by steep density gradients near the limb and shallower gradients in the interior. Under the influence of gaseous dynamical friction, an infalling object's orbit will first decrease in eccentricity, then increase. The critical separation that delineates these regimes is predicted by the local density slope and is linearly dependent on polytropic index. More broadly, our findings indicate that binary systems may routinely emerge from common envelope phases with non-zero eccentricities that were excited by the dynamical friction forces that drove their orbital tightening.
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How the literature uses it
6 arXiv papers cite this in 7 sentences
Papers citing it · 5 sentences without a confident label
Cites it as support 2 papers
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With the BBH orbiting at $ℳ∼1$ near the apoapsis and $ℳ≫1$ near the periapsis, gas drag preferentially drives more eccentricity growth near the apoapsis than eccentricity damping near the periapsis [ref] , thereby monotonically pumping the eccentricity toward unity [ref] .
Dynamical formation of high-eccentricity compact binaries through BH--BH*/TZO collisions · Conclusions · 0.98
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Since the PBH typically enters the host star on a noncircular orbit, and since the retarding forces inside the star may not circularize the orbit (see, e.g., [ref] ), the PBH's orbit is likely to remain eccentric (see also [ref] for a numerical demonstration).
Primordial black hole capture, gravitational wave beats, and the nuclear equation of state · Introduction · 0.97
What it cites · 2 sentences without a confident label
Cites as background 3 papers
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the interactions and capture of stars and compact objects by discs in active galactic nuclei [ref] ; and
Starfall: A heavy rain of stars in 'turning on' AGN · Introduction · 0.95
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the interactions and capture of stars and compact objects by discs in active galactic nuclei [ref] ; and
Effects of an Immortal Stellar Population in AGN Disks · Introduction · 0.95
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Some particularly rich applications have included the dynamics of young stars, and clusters embedded in molecular clouds [ref] ;
Binary evolution, gravitational-wave mergers and explosive transients in multiple-populations gas-enriched globular-clusters · Introduction · 0.93
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