Download Looking Deeper into Astronomy

1-1
I
Looking Deeper into Astronomy
Computers in Astronomical Research
f you ask the average person what astronomers do on the
job, the response will likely be, “They look through
telescopes.” Telescopes for visible light are indeed
important tools of astronomy, and they make the universe
accessible to countless amateur astronomers. Hardly any
professional astronomers actually look through telescopes,
however. Instead, images are recorded electronically using
much the same technology as is found inside a video camera.
(In Chapter 6 of Universe we will see the advantages of this
technology over the human eye.) Other telescopes are
sensitive to invisible forms of light such as X rays or radio
waves; there is no way that one could “look through” such
telescopes. Furthermore, many astronomers seldom, if ever,
even go near a telescope. These researchers analyze new data
or develop theories to explain the data.
The only piece of hardware that is used on a daily basis
by all astronomers is the computer. A number of computers
of different kinds can be found at any modern observatory.
Some are used to control the orientation of the telescope and
to keep it pointed at the object under study; other computers
may regulate the shape of the telescope optics to keep the
image in the sharpest possible focus; and ordinary personal
computers help astronomers keep in contact with their
colleagues around the world through electronic mail.
Perhaps most important, a computer records the data
gathered by the telescope’s electronic detector and saves it
(on magnetic media such as a hard disk) for later study.
Once the stored data are returned to the astronomer’s
office, which may be thousands of kilometers from the
telescope, other computers are used for data analysis. Several
decades ago photographic film was used to record almost all
telescopic images, and extracting all of the information from
such photographs was often a slow and difficult process. But
when images are stored in electronic form, computers can
digest those images directly and process them quickly to
bring out the most subtle details. Many of the astronomical
images in this book were processed in just this way. Software
for this purpose is even available for personal computers and
is used by many amateur astronomers who have electronic
detectors on their telescopes.
Besides their role in collecting and analyzing data,
computers have also changed the character of much
astronomical research in a fundamental way. Consider the
plight of an astronomer who wants to understand why the
galaxy shown in Figure 1-7 (see page 6 of Universe) has
such a beautiful pattern of spiral arms. The answer must lie
in the laws of physics that describe the behavior of the stars
and nebulae that constitute the galaxy. Although these laws
are known, the problem seems completely intractable,
because the galaxy contains an astronomically large number
of stars. An equally large number of intertwined equations
would have to be solved to describe the motions of these
stars, and a scientist with pencil and paper will not live long
enough to solve them. But such problems have become
tractable in recent years with the development of high-speed
supercomputers.
The laws of physics can be written in such a way that
they can be solved by a supercomputer. In their basic form,
the laws of physics are valid at every point in space and
at every moment of time. But scientists seldom need to
apply these laws everywhere at all times. Instead, they
use points in space separated by distances that are small
compared to the size of the object under study. They also
use time intervals that are short compared to the duration
of the process they want to examine. By programming a
supercomputer with the laws of physics expressed only at
these selected points and time intervals, scientists can
reduce a complicated problem to a form that the machine
can handle.
For example, to analyze the spiral galaxy in Figure
1-7, you start with all of the stars at certain positions and
moving with certain speeds. Knowing the gravitational
influences that each star feels from all of the others, you
can compute how each star will move over a brief time
interval. (In a spiral galaxy, individual stars may take
hundreds of millions of years to complete one orbit around
the galaxy’s center, so a “brief” time interval may be a
hundred thousand years or so.) Now you can repeat the entire
t=0
t = 0.5
t = 1.0
t = 1.5
t = 2.0
t = 2.5
(After F. Hohl et al.)
calculation using the data for the stars in their new positions.
Step by step, you compute the motions of all of the stars
within the galaxy. Modern supercomputers are ideal for
performing these repetitive computations.
The accompanying figure shows the result of just such a
calculation using 100,000 simulated stars. The individual
pictures are like frames from a movie, showing how the
simulated galaxy evolves. Note that a spiral structure forms
naturally, although it subsequently fades away. Much of our
present-day understanding of galaxies is based on such
supercomputer simulations.
Using supercomputers, astronomers can simulate
phenomena that might otherwise never be observed. For
example, supercomputers have helped astronomers see how
the Moon might have been created by a Mars-sized object
striking Earth. They have revealed what happens when gas is
captured and swallowed by a black hole. And they have let
astronomers watch as two galaxies, consisting of thousands
of stars and gas clouds, collide and interact with each other, a
process that in reality takes millions of years. These are just a
few examples of the essential role of the computer in modern
astronomy.