Exposing the Stuff Between Stars: A Progress Report on the Canadian Galactic Plane Survey Mapping Our Milky Way Galaxy
Calgary, Alberta
Contact:
Jo Moss
Media Relations Coordinator
(403) 220-5727
Canadian Galactic Plane Survey (CGPS) maps, delineating the gas and dust between stars, reveal the complex
“ecosystem” of our Galaxy, the Milky Way. Highlighting a strip of our Galaxy stretching across 2000 light-years,
a recent panorama (Map 1) exposes, for example, the detailed structure of a giant “spur” known as Lynds
Bright Nebula 679 (Map 2). In their presentation at the American Astronomical Society Meeting in Atlanta
today, Steve Gibson and Russ Taylor of the University of Calgary focus on hydrogen gas clouds that are cold
enough to appear as interstellar silhouettes (Map 3) in this map. This is the first time the cold hydrogen clouds
have been seen in detail, emphasizing the superb quality of the data collected by National Research Council of
Canada’s Dominion Radio Astrophysical Observatory (DRAO). And while the origin of these clouds remains a
mystery, they are suspected of being the first step in the formation of stars out of the stuff between stars.
Taylor says, “Understanding our origins, ultimately from the gas and dust between the stars, requires an
understanding of the Galactic ecosystem. Counterbalancing forces within the dusty, gaseous interstellar medium
govern the cycle of star birth and death. Therefore this medium effects the evolution of the Galaxy as a whole.
The CGPS carried out by an international consortium of universities and observatories, is attempting to reveal
the details of this complex ecosystem.”
The Synthesis Telescope (ST) at DRAO, an array of 7 radio antennas in Penticton, B.C., is responsible for
detecting atomic hydrogen gas for the survey. Invisible to optical telescopes, this gas can only be revealed by
observations of faint radio waves emitted at a wavelength of 21 centimetres. The distribution of antennas
along a 600-metre rail track generates an angular resolution of 1 arcminute, which is more than a factor of 10
better than that in any previous study of the Milky Way. Although the survey is still not complete, the CGPS
data started becoming public, at the Canadian Astronomy Data Centre, August 1999.
Map 1 displays the stuff between stars in the Perseus Spiral Arm of our Milky Way Galaxy by assigning different
colours to radiation not detected by the human eye. Besides DRAO radio data (assigned combinations of blue,
orange, yellow, and green), this composite image includes Infrared Astronomical Satellite (IRAS) data (coloured
pale pink), and data (grey-blue) from the Westerbork Synthesis Radio Telescope (WRST) in the Netherlands.
The location on the night sky of this panoramic strip is displayed in Diagram 1 while its position in the Milky Way
relative to our Sun is presented in the “top view” schematic in Diagram 2.
The diffuse nebulosity that fills the Map 1 panorama from left to right is hydrogen gas, which is distributed
along the mid-plane of the Galactic disk and runs across the middle of the image. However CGPS astronomers
used the DRAO array to isolate the gas in the Perseus Arm, 6500 light-years distant, from the rest of the gas
in the disk. Overlaid on these hydrogen data are IRAS images of the dust that intersects our line of sight
through the disk. The point-like sources (WRST) are mainly distant galaxies that have very energetic cores
called Active Galactic Nuclei.
Far from a homogeneous environment, the interstellar medium in the Perseus Arm shows a highly disturbed and
seemingly chaotic appearance. This region has been shaped partly by the ongoing formation of massive, hot
stars near the hot dusty clouds (appearing pink) of the W3, W4 and W5 regions right of centre, and perhaps
also by the passage of a large scale spiral shock wave as the matter in the Perseus Arm orbits around the
centre of the Galaxy.
A giant “spur” seen in the Perseus Arm panorama, and detailed in Map 2, is interstellar gas and dust emerging
from the disk of our Milky Way Galaxy. Seen against a backdrop of distant quasars, Lynds Bright Nebula 679 is
over 200 light years in extent and apparently driven out of the disk of the galaxy by giant interstellar shock
waves. Lying in the constellation Perseus, the spur is over 2 degrees in angular extent, about four moon
diameters. At the surface of the spur lies an interface between the cool and hot matter forming the diffuse
interstellar medium. On the left side, facing the plane of the galaxy the material in the spur consists of cold
hydrogen gas and warm dust. On the side facing away from the plane of galaxy the spur is being evaporated
by ultraviolet radiation. The hot gas being driven off the spur can be seen as a faint green halo arising from
hot, fluorescing hydrogen gas.
Despite the violent motions in the interstellar medium and the impact of energetic radiation, pockets of
quiescence exist where gas clouds can cool and condense, leading to the formation of the next generation of
stars. Map 3 magnifies a section of Map 1 exposing clumps and filaments of cold hydrogen gas silhouetted
against the hotter diffuse hydrogen. These interstellar silhouettes appear purple-ish due to the colours assigned
to the DRAO hydrogen dataset. The origin of these clouds is still a mystery, but they may be first step in the
evolution of the diffuse interstellar gas to a cold, dense state in which molecules can coalesce, clouds collapse,
and new stars form.
NOTES TO EDITORS:
SCIENCE CONTACT INFORMATION:
Interstellar Silhouettes:
Dr. Steven J. Gibson
Department of Physics and Astronomy
University of Calgary
2500 University Drive, N.W.
Calgary, Alberta
Canada T2N 1N4
Phone: (403) 220-8015
Fax: (403) 289-3331
Email: gibson@ras.ucalgary.ca
Other:
Dr. A. Russ Taylor
Department of Physics and Astronomy
University of Calgary
2500 University Drive, N.W.
Calgary, Alberta
Canada T2N 1N4
Phone: (403) 220-5385
Fax: (403) 289-3331
Email: russ@ras.ucalgary.ca
IMAGE CONTACT INFORMATION:
Dr. Jayanne English
Space Telescope Science Institute
3700 San Martin Dr.
Baltimore, MD 21211
USA
Phone: (410) 338-4352
Fax: (410) 338-5090
Email: jenglish@stsci.edu
MAP CREDIT:
Dr. Jayanne English (CGPS/STScI) using data acquired by the Canadian Galactic Plane Survey (NRC/NSERC) and
produced with the support of Russ Taylor (U. of Calgary).
On January 14, 2000 full resolution tiffs of these 3 images and 2 diagrams, along with other images from the
CGPS will be available at
http://www.stsci.edu/~jenglish/cgps/pr/pr_14012000.html
