Gravitational scattering is the alteration of trajectories when two or morecelestial objects exchangeenergy and momentum through closegravitational encounters.^[1] This process underpins many dynamical phenomena inastrophysics, from the formation ofbinary star systems to the ejection of bodies fromplanetary systems.^[1] When objects likestars,planets, orblack holes pass close enough to influence each other’s motions, their paths can shift dramatically.^[2] Close passages between massive objects—such asstars,planets, orblack holes—can produce eitherbound pairs or unboundejecta.^[3] An example isJupiter scatteringKuiper belt objects out of theSolar System.^[4]

Researchers investigate gravitational-scattering events withN-body simulations and other numerical models of gravitational fields andgravitational field interactions.^[1][4] A key aspect is theexchange of energy and momentum between the bodies.^[5] For example, a fast body can impartkinetic energy to a slower one, producing theslingshot effect exploited by spacecraft duringgravitational-assist flybys.^[6]

Observational evidence of scattering clarifies several astrophysical problems, fromstellar-cluster evolution togalaxy-core dynamics.^[1] In dense regions such asstar clusters, scattering influences star formation rates and the spatial distribution of stellar populations.^[7]Hypervelocity stars are thought to originate when massiveblack holes scatterbinary stars at galactic centers.^[3] Close encounters between compact objects can emitgravitational waves, which have been detected by observatories such as theLaser Interferometer Gravitational-Wave Observatory (LIGO).^[8] Analyses employ bothNewtonian mechanics andgeneral relativity; the relativistic framework is essential for high-mass or high-speed encounters.^[9]

Gravitational scattering can alter orbits and in extreme cases can eject celestial bodies from their native planetary systems.^[3] One mechanism for shifting planets to wider orbits is scattering by massive neighbours; within aprotoplanetary disk, similar kicks can arise from dense gas clumps.^[10] In theSolar System,Uranus andNeptune may have been pushed outward after close encounters withJupiter orSaturn.^[11][4] After the protoplanetary gas dissipates, multi-planet systems can experience comparable instabilities: orbits shift, and some planets are eventually ejected or spiral into the host star.^[11][4]

Planets scattered gravitationally can end on highlyeccentric orbits withperihelia close to the star, enabling their orbits to be altered by thegravitational tides they raise on the star.^[12] The eccentricities and inclinations of these planets are also excited during these encounters, providing one possible explanation for the observed eccentricity distribution of the closely orbitingexoplanets.^[12] The resulting systems are often near the limits of stability.^[13] As in theNice model, systems of exoplanets with an outer disk ofplanetesimals can also undergo dynamical instabilities followingresonance crossings during planetesimal-driven migration.^[4][14] The eccentricities and inclinations of the planets on distant orbits can be damped bydynamical friction with the planetesimals with the final values depending on the relative masses of the disk and the planets that had gravitational encounters.^[14]

• Celestial mechanics
• n-body problem
• Planetary migration
• Three-body problem
• Stellar dynamics
• Stellar kinematics

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• Astrophysics
• Astrodynamics
• Astronomical dynamical systems
• Celestial mechanics
• Effects of gravity
• Gravity
• Orbital maneuvers
• Orbits
• Solar System dynamic theories
• Stellar dynamics

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