277
See also: Stellar composition 162–63 ■ Nuclear fusion within stars 166–67 ■ Energy generation 182–83 ■
Dense molecular clouds 200–01 ■ Studying distant stars 304–05 ■ Jeans (Directory) 337 ■ Ambartsumian (Directory) 338
Shu and his colleagues Fred
Adams and Susana Lizano at the
University of California at Berkeley
presented their model in 1986 after
20 years of work.
The inside-out model
Shu’s system is called the “singular
isothermal model,” or the “inside-
out model.” It is built from the
complex mathematics that define
the dynamics of gas clouds, taking
into account factors such as
temperature, density, electrical
charge, and magnetism. Shu’s
model works by making the process
self-similar. A starting condition
that causes some of the gas cloud
to contract into a dense core will
result in the same—or similar—
conditions, which cause more
gas to join the core, and so on.
This process was found to be
stable enough to keep the young
star together as it grew. Earlier
models had failed because they
could not find a way to balance
the mechanisms that were pulling
the gases in and pushing heat out;
as a result, these models ended
with the young star disintegrating.
GMCs are vast regions of the
galaxy filled with hydrogen atoms
and molecules mixed with specks
of dust and ice. Typically, a GMC
contains 100,000 solar masses of
material, which is a mixture of
primordial gases produced by the
Big Bang and the remnants of long-
dead stars. GMCs are mostly found
in the spiral arms of a galaxy.THE TRIUMPH OF TECHNOLOGY
In the mid-1960s, Shu and the
renowned Chinese−American
mathematician Chia-Chiao Lin
modeled the rotation of a spiral
galaxy, and showed that the arms
are located at density waves—
“traffic jams” of stars. Such density
waves sweep up interstellar
material into GMCs, and this
triggers the formation of stars. ❯❯The Pillars of Creation are vast clouds
of gas and dust where new stars are
made. This famous image was captured
by the Hubble Space Telescope in 1995.
Stars are dense balls of
superhot hydrogen.Material from near
the middle contracted
first, and then drew
in the outer regions.They must have formed
from clouds of hydrogen
gas in interstellar space.Stars form from the inside out.