At the Center
of the Milky Way
the nature and appearance of our galaxy is no small feat, for we
live within a disk of obscuring gas and dust.
Our sun is part
of a large disk made up of stars and large clouds of molecular and
atomic gas in motion around the Galaxy's center. Our solar system
orbits this center, located about 30,000 light-years away from Earth,
at 500,000 miles per hour. It takes our solar system 200 million
years to make a single orbit of the galaxy.
can infer the shape and appearance of our galaxy from elaborate
observations, and as a result have created maps of our galaxy. Yet
parts of the Milky Way remain hidden-blocked by light-years of obscuring
material (gas and dust) spread between the stars.
is working to penetrate the mysteries of this interstellar material.
Ghez is an astronomer at the University of California at Los Angeles
and an NSF Young Investigator, a national award given to outstanding
faculty at the beginning of their careers. Her observations of the
central regions of the Milky Way have permitted her to examine its
very heart. Ghez, like many others, theorized that the Galaxy's
core is the home of a supermassive black hole. "Although the notion
has been around for more than two decades, it has been difficult
to prove that [a black hole] exists," says Ghez. Now it appears
her observations offer that proof.
one of the two W. M. Keck ten-meter telescopes on Mauna Kea in Hawaii,
Ghez looked at the innermost regions of the Galaxy's core. For three
years, she studied the motions of ninety stars. While scientists
already knew that those stars nearest the center of the Galaxy move
quickly in their orbits, Ghez was astonished to discover that the
stars nearest the center of the Milky Way were moving at speeds
as high as three million miles per hour. Only a very large assembly
of superconcentrated mass inside the stars' orbits could whip them
around at those speeds. "The high density we observe at the very
center of the Milky Way exceeds that inferred for any other galaxy,
and leads us to conclude that our galaxy harbors a black hole with
a mass 2.6 million times that of the Sun," Ghez notes.
do not think that a supermassive black hole at the center of a galaxy
is unique to the Milky Way. Rather, it appears to be quite typical
of the almost innumerable galaxies in the observable universe. The
fact that black holes may be the rule rather than the exception
makes it even more important that we continue to study them.