A kinematic resonance hypothesized to explain the existence of galactic
→ spiral arms. It occurs
when the frequency at which a star encounters
the spiral → density wave is a multiple of its
→ epicyclic frequency.
Orbital resonances occur at the location in the disk where
Ωp = Ω ± κ/m,
where Ωp is → pattern speed, κ
→ epicyclic frequency, and m an integer representing
the number of spiral arms. The minus sign
corresponds to the inner Lindblad resonance (ILR) and the plus sign to the
outer Lindblad resonance (OLR). The corotation resonance
corresponds to Ωp = Ω. In general, the Lindblad resonances
are defined for two spiral arms (m = 2), and low order. There are other
less important resonances corresponding to higher m values.
These resonances tend to increase the object’s orbital eccentricity and to cause its
longitude of periapse to line up in phase with the perturbing force.
Lindblad resonances drive spiral density waves both in galaxies (where stars
are subject to forcing by the spiral arms themselves) and in Saturn’s
rings (where ring particles are subject to forcing by Saturn’s moons).
See also: After the originator of the model, Bertil Lindblad (1895-1965),
a Swedish astronomer, who made important contributions to the
study of the rotation of the Galaxy; → resonance.
