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Joined 2026-09-21 Message
Incoming links: Juri Toomre
Alar Toomre Created 2026-10-20 Updated 2026-11-05
Alar Toomre connected the stability of a stellar galactic disk to the competition between self-gravity, rotation and random stellar motion. His 1964 analysis gave a local axisymmetric stability criterion, commonly expressed through the Toomre parameter. A dynamically cold disk can be more vulnerable to gravitational structure formation than one with larger velocity dispersion.[ref]
On the Gravitational Stability of a Disk of Stars by Alar Toomre. p. 1217, abstract and local stability problem
With Juri Toomre, he also modeled the tidal bridges and tails of interacting galaxies. Their test-particle encounters showed how gravity alone can draw long structures out of rotating galactic disks.[ref]
Portrait of Alar Toomre
. Via Wikimedia Commons; credits and usage information are on the linked source file page. Source.
Juri Toomre Created 2026-10-20 Updated 2026-11-05
Juri Toomre and Alar Toomre demonstrated how close gravitational encounters between galaxies can generate long bridges and tails. Their 1972 calculations represented each galactic disk by noninteracting test particles orbiting a central mass, then followed its response to another passing galaxy.
Despite this deliberately simplified model, tidal forces produced narrow extended structures resembling observed interacting systems. The paper reconstructed several particular pairs, connecting recognizable morphology to encounter geometry. It showed that dramatic luminous extensions can arise from ordinary gravity acting on pre-existing disk material.[ref]
Portrait of Juri Toomre
. External portrait hosted by JILA, University of Colorado Boulder. Source.