Using NASA's orbiting
Far Ultraviolet
Spectroscopic Explorer, a team of astronomers from
Johns Hopkins and elsewhere has taken an unprecedented peek
beneath the "skirts" of the tunic-clad Orion the Hunter and
come away with observations that may lead to enhanced
knowledge of how interstellar dust absorbs and scatters
ultraviolet starlight.
"Understanding interstellar dust is important. After
all, this is the stuff out of which, ultimately, planets,
stars and even people are made," said team member Richard
Conn Henry, a professor in the Henry A. Rowland
Department of Physics
and Astronomy in the Krieger School. Henry presented
findings from the research on Jan. 11 during the American
Astronomical Society's meeting in San Diego.
The constellation Orion, named for its resemblance to
a powerful, tunic-clad hunter wielding a club and sword, is
probably the greatest star factory in our galaxy, with
thousands of young, hot, blue stars emerging from its great
clouds of gas and dust. Led by Jayant Murthy of the Indian
Institute of Astrophysics, the team examined data FUSE
recorded near the most active region of current star
formation.
What they saw surprised them.
"FUSE detected a spectrum of ultraviolet light in a
region where there is no star at all," said Murthy, who
spent many years at Johns Hopkins before going to the
Indian Institute. "The spectrum is of light reflecting from
the dust in a region near a quite bright star, whose
spectrum is very similar to that of the reflected light we
detected. At first we thought that particular star was the
original source of the light. But a closer look revealed
that despite the similarity, there were differences —
differences striking enough to allow us to conclude that
the star in question could not be the source of the light
that is scattering from the dust. So where was that light
coming from?"
Team members suspect that the light in question
emanated from "the Trapezium," a cluster of stars located
in the heart of the Orion Nebula. So named because the
configuration of its stars resembles a geometric
quadrilateral with two parallel sides, the Trapezium not
only is one of the most famous multiple star systems in the
night sky but is also — at only about 1 million years
old — the youngest.
"The ultimate aim of this work is to understand
exactly in what manner the light gets reflected: What is
this interstellar dust from which the stars are born?" asks
David Sahnow, a research scientist in the Department of
Physics and Astronomy at Johns Hopkins and a member of the
investigating team. "To what extent does the dust absorb
the light, and to what extent does it scatter it? For that
light which is scattered, does it go backward, forward or
sideways?"
Perhaps one of the most interesting aspects of this
investigation into interstellar dust is that it happened
serendipitously.
"This is a great example of how science works
sometimes, how you can stumble across something valuable
while looking for something else," Murthy said. "We were
actually taking engineering tests at some semi-random
places in the sky while FUSE was thermalizing, and we
noticed this. Our discovery that FUSE's high spectral
resolution can actually be applied to diffuse radiation has
additional ramifications. High spectral resolution is often
a key to physical understanding, and our Orion observation
shows that we will be able to use this technique to more
deeply understand the general diffuse background radiation
over the sky."
The team's paper on its observations of Orion has been
accepted for publication by the Astrophysical Journal.
NASA funded this research, and the team hopes the
agency will underwrite further investigations. "We have
submitted a proposal to NASA to use FUSE over the next year
to explore the ramifications of our surprise discovery that
FUSE can detect diffuse emission," Henry said. "By choosing
targets carefully, we can get more easily interpreted data,
allowing stronger conclusions regarding the nature of
interstellar dust. The observed cosmic background is not
fully understood and possibly is of new cosmological
importance. We are confident that with FUSE and carefully
implemented further observations, we can answer many
questions for the first time."
Although it was reported two weeks ago that FUSE
operations had been suspended because of a mechanical
problem, the Johns Hopkins team that operates the satellite
is confident that work will resume shortly.