A galaxy far beyond our own Milky Way, with a monstrous, churning
black hole in its center, has been observed by two optical telescopes
working in unison as an interferometer. These observations reveal the
finest level of detail in a galaxy ever produced at infrared
wavelengths.

Two linked telescopes at the W.M. Keck Observatory on Mauna Kea,
Hawaii, observed the inner regions of the galaxy NGC 4151. The Keck
Interferometer combines the world’s two largest optical telescopes. A
paper on the findings will appear in the October 20 issue of the
Astrophysical Journal Letters.

NGC 4151 is 40 million light years from Earth, far beyond the most
distant object previously detected by this type of telescope system,
which was about 3,000 light years from Earth.
These observations marked the first time an optical/infrared
interferometer detected any object outside our galaxy and were
followed a few weeks later by observations of a second galaxy with the
European Southern Observatory’s Very Large Telescope Interferometer.

“This opens a whole new area of research on galaxies other than our
own,” said Dr. Rachel Akeson, an astronomer at the Michelson Science
Center at the California Institute of Technology in Pasadena. The Keck
Interferometer, with its 10-meter (33-foot) telescopes, has the
sensitivity needed to detect objects outside our galaxy.

The Keck Interferometer gathers light waves with two telescopes, then
combines the waves so they interact, or “interfere” with each other.
The system transports the light to a laboratory located between them,
where a beam combiner and infrared camera combine and process the
light. This technique simulates a much larger, more powerful
telescope. In this respect, the Keck Interferometer is equivalent to
an 85-meter (279-foot) telescope.

“Interferometry provides the angular resolution, or ability to resolve
fine details, to make these kinds of observations,” said the
interferometer system architect, Dr. Mark Colavita of NASA’s Jet
Propulsion Laboratory, Pasadena, Calif.

“We couldn’t observe objects as faint as this galaxy before with an
interferometer. Adaptive optics on 10-meter telescopes provides the
sensitivity to make this observation,” said Dr. Peter Wizinowich,
interferometer team lead for the W.M. Keck Observatory at the
California Association for Research in Astronomy, Kamuela, Hawaii.

NGC 4151, well studied with telescopes and instruments at many
wavelengths, is believed to have a black hole at its center surrounded
by a doughnut-shaped ring of dust. The black hole is estimated to be
10 million times as massive as our Sun, and 10 times more massive than
the black hole at the center of our own galaxy, the Milky Way. Like
all black holes, its gravitational pull is so powerful that nothing,
not even light, can escape. However, as it gobbles up nearby material,
a fraction of the material is spit out in a jet.

“We’re interested in studying galaxies with massive black holes,” said
Dr. Mark Swain, a JPL astronomer and lead author of the paper. “We
found that emission in NGC 4151 was unexpectedly compact. This
indicates the light we saw is likely coming from a disc of material
falling into the massive black hole.”

The observations were made on May 19 and 20, 2003, by a team of
scientists from JPL, the California Association for Research in
Astronomy, and the Michelson Science Center. Akeson, Colavita, Swain
and Wizinowich are part of the team.

The Keck Interferometer is part of NASA’s Origins Program, which seeks
to answer the questions: Where did we come from? Are we alone? The
development of the Keck Interferometer is managed by JPL for NASA’s
Office of Space Science, Washington, D.C. JPL is a division of the
California Institute of Technology. The W.M. Keck Observatory is
funded by Caltech, the University of California and NASA, and is
managed by the California Association for Research in Astronomy,
Kamuela, Hawaii.

Additional information is available at

http://keck.jpl.nasa.gov/ .