Embargoed For Release: 11:15 a.m., CMT, Tuesday, June 1, 2004
Contact:
Charles Blue, Public Information Officer
Charlottesville, VA
(434) 296-0323
cblue@nrao.edu
Origin of Enigmatic Galactic-center Filaments Revealed
Twenty years ago, astronomers discovered a number of
enigmatic radio-emitting filaments concentrated near
the center of the Milky Way Galaxy. These features initially
defied explanation, but a new study of radio images of the
Galactic center may point to their possible source.
By combining data from the National Science Foundation's
Very Large Array (VLA) and
Robert C. Byrd Green Bank Telescope (GBT) astronomer Farhad
Yusef-Zadeh of Northwestern University has found evidence that
at least some of the filaments spring from the concentrated
star-formation regions that populate the Galactic center.
Combined VLA and GBT image (green)
of the Galactic center, with red inset of GBT
data only (red). Bright region on right is
location of supermassive black hole. Linear
filaments are visible above this area.
CREDIT: NRAO/AUI/NSF Yusef-Zadeh, et.al.
(Click on Image for Larger Version)
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Yusef-Zadeh presented his findings at the Denver, Colorado, meeting of the
American Astronomical Society.
William Cotton of the National Radio Astronomy Observatory (NRAO)
in Charlottesville, Virginia, and William Hewitt of Northwestern
University also contributed to this research.
"Astronomers have long puzzled over the cause of these striking
features," said Yusef-Zadeh, "and the turbulent nature of the
Galactic center has made detailed analysis difficult. With
new multi-wavelength radio images of the Galactic center,
however, we can finally see a link between areas of starburst
activity and these long-linear filaments."
The filaments, which range from 10 to 100 light-years
in length and are perhaps little more than 1 to 3 light-years
across, occur only in a very narrow area, within approximately
two degrees of the Galactic center (which translates to
approximately 900 light-years across).
Early theories about the origin of these filaments suggested
that they were somehow related to the Milky Way’s own magnetic field.
This was due to the fact that the first filaments detected were
oriented perpendicular to the plane of the Galaxy, which would
have aligned them with the Galaxy’s own magnetic field.
"The problem with this hypothesis is that more recent images
have revealed a population of weaker filaments oriented
randomly in relation to the plane of the Galaxy," said
Yusef-Zadeh. "This makes it difficult to explain the
origin of the filaments by an organized Galactic magnetic field."
In March and June of 2004, a team of astronomers using the
GBT made images of the Galactic center at various wavelengths.
The purpose of these surveys was to help identify radio features
produced by hot gas (thermal emission) and those produced
in magnetic fields (non-thermal emission). In general, thermal
features radiate more strongly at shorter wavelengths and
non-thermal at longer wavelengths.
By comparing the GBT images with earlier VLA data taken of
the same region, Yusef-Zadeh determined that a number of the
non-thermal filaments seemed to connect to concentrated
areas of thermal emission, which identify pockets of star formation.
Combined radio image from the Very
Large Array and Green Bank Telescope. The linear
filaments near the top are some of the nonthermal
radio filaments (NRFs) studied by the researchers.
Other features, such as supernova remnants (SNRs) and
the area surrounding our Galaxy's supermassive
black hole (Sgr A) are shown.
CREDIT: NRAO/AUI/NSF Yusef-Zadeh, et.al.
(Click on Image for Larger Version)
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"What this showed us is that two seemingly disparate processes,
thermal and non-thermal radio emission, can be created by the
very same phenomenon," said Yusef-Zadeh. "In this case, that
phenomenon is pockets of starburst activity."
Yusef-Zadeh notes that the exact mechanism for how the areas of
starburst generate the magnetic fields is still being investigated.
"There are many ideas about the mechanism that generates these
filaments," added Yusef-Zadeh, "but one possibility is that they
are produced by the collision of winds blown off from individual stars."
The star-forming regions associated with the filaments
may contain about 100 massive stars each.
The center of the Milky Way Galaxy is shrouded from optical
telescopes by dense clouds of dust and gas. Radio telescopes,
however, are able to pierce through the optical veil and see
the features within. Concealed at the very heart of our Galaxy is
a supermassive black hole. Known as Sagittarius A* (pronounced A-star),
this area is a very powerful source of radio waves and was first
detected by Karl Jansky in 1932.
While the VLA can image fine scale structures with great precision,
it can not always detect extended radio emission.
The GBT, however, can help fill in the gaps. Together,
they create a more complete image than either instrument could
produce separately. "The ability to combine the data from the
two telescopes," said Cotton, "gives us a very powerful tool for
understanding how the smallest features relate to the overall structure.
This is particularly important when you want to study an area
like the center of our Galaxy."
In addition to Yusef-Zadeh, Hewitt, and Cotton, the
GBT survey was conducted by Casey Law and Douglas Roberts of
Northwestern University; and Ron Maddalena of the National
Radio Astronomy Observatory.
The VLA is a single radio telescope made up of 27 separate
antennas located on the Plains of San Agustin near Socorro, New Mexico.
The GBT is the world’s largest fully steerable radio telescope,
and it is located in Green Bank, West Virginia.
Both telescopes are operated by the NRAO.
The
National Radio Astronomy Observatory is a facility of the
National Science Foundation, operated
under cooperative agreement by
Associated Universities, Inc.
Modified on
Tuesday, 01-Jun-2004 08:18:25 EDT
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