Journal Article

Radial-orbit instability in modified Newtonian dynamics

Carlo Nipoti, Luca Ciotti and Pasquale Londrillo

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 414, issue 4, pages 3298-3306
Published in print July 2011 | ISSN: 0035-8711
Published online July 2011 | e-ISSN: 1365-2966 | DOI:
Radial-orbit instability in modified Newtonian dynamics

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The stability of radially anisotropic spherical stellar systems in modified Newtonian dynamics (MOND) is explored by means of numerical simulations performed with the N-body code n-mody. We find that Osipkov–Merritt MOND models require for stability larger minimum anisotropy radii than equivalent Newtonian systems (ENSs) with the dark matter, and also than purely baryonic Newtonian models with the same density profile. The maximum value for stability of the Fridman–Polyachenko–Shukhman parameter in MOND models is lower than in ENSs, but higher than in Newtonian models with no dark matter. We conclude that MOND systems are substantially more prone to radial-orbit instability than ENSs with dark matter, while they are able to support a larger amount of kinetic energy stored in radial orbits than purely baryonic Newtonian systems. An explanation of these results is attempted and their relevance to the MOND interpretation of the observed kinematics of globular clusters, dwarf spheroidal and elliptical galaxies is briefly discussed.

Keywords: gravitation; instabilities; globular clusters: general; galaxies: kinematics and dynamics; dark matter

Journal Article.  6041 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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