A Lindblad resonance, named for the Swedish galactic astronomer

Bertil Lindblad Bertil Lindblad (26 November 1895 – 25 June 1965) was a Swedish astronomer. After finishing his secondary education at Örebro högre allmänna läroverk, Lindblad matriculated at Uppsala University in 1914. He received his ''filosofie mag ...

, is an

orbital resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relation ...

in which an object's epicyclic frequency (the rate at which one

periapse An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

follows another) is a simple multiple of some forcing frequency. Resonances of this kind tend to increase the object's

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values be ...

and to cause its longitude of periapse to line up in phase with the forcing. Lindblad resonances drive spiral density waves both in

galaxies A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar Sys ...

(where stars are subject to forcing by the spiral arms themselves) and in

Saturn's rings Saturn has the most extensive and complex ring system of any planet in the Solar System. The rings consist of particles in orbit around the planet made almost entirely of water ice, with a trace component of rocky material. Particles range fro ...

(where ring particles are subject to forcing by Saturn's moons). Lindblad resonances affect stars at such distances from a

disc galaxy A disc galaxy (or disk galaxy) is a galaxy characterized by a galactic disc. This is a flattened circular volume of stars that are mainly orbiting the galactic core in the same plane. These galaxies may or may not include a central non-disc-like ...

's centre where the natural frequency of the radial component of a star's orbital velocity is close to the frequency of the gravitational potential maxima encountered during its course through the spiral arms. If a star's orbital speed around the galactic centre is greater than that of the part of the spiral arm through which it is passing, then an inner Lindblad resonance occurs—if smaller, then an outer Lindblad resonance. At an inner resonance, a star's orbital speed is increased, moving the star outwards, and decreased for an outer resonance causing inward movement.

References

External links

Three-Dimensional Waves Generated At Lindblad Resonances In Thermally Stratified Disks – Lubow & Ogilvie
Concepts in astrophysics Stellar dynamics Orbital perturbations Orbital resonance {{scattering-stub

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