Alar Toomre

Alar Toomre (born 5 February 1937 in Rakvere) is an Estonian-American astronomer and mathematician. He is a professor of applied mathematics at the Massachusetts Institute of Technology. Toomre's research is focused on the dynamics of galaxies.

Following the Soviet occupation of Estonia in 1944, Toomre and his family fled to Germany; they emigrated to the United States in 1949. He received an undergraduate degree in Aeronautical Engineering and Physics from MIT in 1957 and then studied at the University of Manchester on a Marshall Scholarship where he obtained a Ph.D. in fluid mechanics.

Toomre returned to MIT to teach after completing his Ph.D. and remained there for two years. After spending a year at the Institute for Advanced Studies, he returned again to MIT as part of the faculty, where he stayed. Toomre was appointed an Associate Professor of Mathematics at MIT in 1965, and Professor in 1970.

In 1964, Toomre devised a local gravitational stability criterion for differentially rotating disks. It is known as the Toomre stability criterion, which is usually measured by a parameter denoted as Q. The Q parameter measures the relative importance of vorticity and internal velocity dispersion (large values of which stabilise) versus the disk surface density (large values of which destabilise). The parameter is constructed so that Q<1 implies instability.

Toomre collaborated with Peter Goldreich in 1969 on the subject of polar wander, developing the theory of polar wander. Whether true polar wander has been observed on earth, or apparent polar wander is accountable for all the observations of paleomagnetism remains a controversial issue.

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