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**Session 20 - HAD II - New Telescopes and New Tools.**

*Division, Oral session, Monday, June 08*

*DeAnza/Mesa, *

## [20.01] Beginning Computer Modeling for the Structure and Evolution of the Stars

*K. H. Olsen (GCSI, Lynnwood, WA)*
Vastly improved understanding of the internal structure and
evolution of the stars is one of the extremely successful
accomplishments of late 20th century physics and
astrophysics. Electronic computers played an essential and
pivotal role in the theoretical phases of these
developments. Theoreticians had attempted to construct
mathematical models of stars since the late nineteenth
century, but growth of understanding was slow because:
The requisite atomic and nuclear physics was then largely
unknown; (2) The four simultaneous non-linear partial
differential equations of stellar structure were impossible
to solve analytically, thus requiring questionable
approximations or extremely tedious and error-prone
large-scale numerical integrations with hand-operated
mechanical calculators. By 1940 some important basic
properties of white dwarfs and main-sequence stars had been
deduced but most other stellar types in the
Hertzsprung-Russell diagram remained puzzles.

Urgent computational needs of the Manhattan Project and its
immediate post-war extensions greatly spurred the invention
and rapid development of modern, high-speed, stored-program
electronic computers. Simultaneously, new numerical
techniques were conceived to take full advantage of the
unique capabilities of the new machines. John von Neumann
and Los Alamos associates were highly influential in both of
these revolutions. Many problems important for the nuclear
laboratories required detailed solutions to complex
equations similar to the basic equations of stellar
structure. Thus, when Martin Schwarzschild, Louis Henyey,
Marshal Wrubel and their students and collaborators began
applying modern computers to problems in stellar physics,
they often had to explore new numerical techniques to fit
their own problems. This paper outlines how astrophysicists
adapted their insights, thinking and working methods in
beginning the transition to computer modeling which came to
totally dominate the field by the late-1960s.

The author(s) of this abstract have provided an email address for comments about the abstract: kolsen@geophys.washington.edu

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