Astronomy - At the Center of the Milky Way
At the Center
of the Milky Way
Understanding    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.
Astronomers    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.
Andrea Ghez    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.
Using    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.
Astronomers    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.