CCA Seminar: Smadar Naoz

Date & Time

Smadar Naoz, UCLA
Title: “On the Dynamics of Planets and also Stars and Black Holes –
New Insights from Triples”

Abstract: Many observed triple systems in our Universe are in a
hierarchical configuration: two objects orbit each other in a
relatively tight inner binary while the third object is on a much
wider orbit. Furthermore, the secular approximation for the evolution
of hierarchical triple body systems has been proven to be very useful
in many astrophysical contexts, from planetary to triple-star systems
and even black holes. In this approximation, the orbits may change
shape and orientation, on timescales longer than the orbital periods,
but the semi-major axes are constant. In early studies of hierarchical
secular three-body systems (Kozai 1962; Lidov 1962), the wider orbit
was set to be circular, and one of the tight binary members was
assumed to be a test (massless) particle. In this situation, the
component of the tight orbit’s angular momentum along the total
angular momentum is conserved, and the lowest order of the
approximation (i.e., the quadrupole approximation) is valid. I will
discuss recent developments that showed that considering systems
beyond the test particle approximation, or circular orbits, requires
the next level of approximation for a correct representation of the
physics, called the octupole-level. This leads to qualitative
different behavior of the system. In this case, the angular momenta
component of the tight and wide orbits along the total angular
momentum is not conserved. Most interestingly, at this level of
approximation, for an eccentric wide orbit, the tight orbit can reach
extremely high eccentricities and undergo chaotic flips of its
orientation. This behavior has important implications for the
evolution of many systems, and I will present some nominal examples,
such as retrograde hot Jupiters, blue stragglers, and low-mass X-ray

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