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NEW
MAP OF MILKY WAY CHARTS WHERE STARS ARE BORN
Boston
University scientists produce clearest images of star-forming
clouds
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A blow-up of
one region of intense star formation known as W51, located at
about 15,000 light-years from the Earth.
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(Boston) – A team of
astronomers from Boston University’s Institute for
Astrophysical Research has produced the clearest map to-date of
the giant gas clouds in the Milky Way that serve as the
birthplaces of stars. Using a powerful telescope, the astronomers
tracked emissions of a rare form of carbon monoxide called 13CO
to chart a portion of our home galaxy and its star-forming
molecular clouds.
The researchers hope the new
illustration will aid in the identification of additional clouds
and study of their internal structure to better understand the
origin of stars like the sun, which began its life in such a
cloud about 5 billion years ago. The data and images are
published in the March issue of the Astrophysical Journal
Supplement.
The eight-year project, called the Boston
University-Five College Radio Astronomy Observatory (FCRAO)
Galactic Ring Survey (GRS), was led by a team of astronomers
based at BU, the University of Cologne in Germany, and the
University of Massachusetts.
To produce the detailed
image, the astronomers mapped the location of 13CO in the Milky
Way using a large radio telescope operated by the FCRAO of the
University of Massachusetts that captures and images radio
emissions at a frequency near 100,000 MHz – about 1,000
times higher than FM stations. When viewed in the emission from
13CO, the clouds are far more transparent than the more
traditionally studied 12CO which allowed the team to peer more
deeply into their interior.
“The value of such high
range imaging is that it enables us to identify the underlying
patterns of gas distribution and speeds that point toward the key
physical processes occurring within the molecular gas phase of
the interstellar medium,” said Dr. Mark Heyer, a researcher
from UMass involved in the project.
Using a new receiver
developed at UMass, the astronomers could depict the structure of
the clouds faster and with much finer detail than any previous
attempts. As an added benefit, the distribution of the clouds
also delineates the spiral structure of the Milky Way.
“Ironically, because we live inside the Milky Way,
we know more about the shapes of far more distant galaxies better
than our own,” said James Jackson, astronomy professor at
BU and lead investigator of the study. “The GRS map helps
us better understand the configuration of our home galaxy and its
components.”
“Upon seeing the GRS image, I
knew right away it was something terrific. It was like the first
time I put on glasses as a kid, and wondered how I ever got along
without knowing about every shape, contour and detail of the
world around me,” said Dr. Ronak Shah, a researcher from BU
who worked on the project. “The GRS has that affect on a
lot of us. We thought we understood the Milky Way and then the
GRS revealed so much more detail to explore.”
According
to Dr. Robert Simon, now at the University of Cologne, but who
started the project with Jackson in 1998 at BU, the information
from the GRS will constitute an important new database for the
study of molecular clouds and Milky Way structure for generations
of astronomers.
The scientists are now closely analyzing
the image and one of the initial findings is the probable
identification of dark, cold molecular clouds in the earliest
stages of star development.
“Data from the Galactic
Ring Survey have shown that these clouds are the counterparts to
active, bright star-forming clouds, but because they have not yet
been heated by the embedded stars, they are much colder and
quieter,” said Jackson. “Follow-up studies of these
clouds will provide additional important clues about the origin
of stars since we’ll be able to examine them at an earlier
point in their life.”
Another interesting result is
that all of the molecular clouds studied so far have similar
lumpy structures, regardless of their size, mass, and
star-forming activity. These lumps will eventually become stars
and, according to the researchers, this similarity suggests that
all clouds form stars of various masses in roughly the same
proportion.
The Milky Way is a vast disk of 100 billion
stars, gas, and dust and because it is flat, the map is long and
narrow. Since most of the Galaxy lies in the Southern skies,
unreachable from Northern Hemisphere telescopes, and because many
of the molecular gas clouds are concentrated toward its inner
regions, only a portion was imaged.
The Institute for
Astrophysical Research (IAR) was founded in 1998 in order to
promote and facilitate research and education in astrophysics at
Boston University. The IAR supports research by BU Astronomy
faculty members, graduate and undergraduate students, and
postdoctoral and senior research associates. In addition, the IAR
manages and coordinates the use of astrophysical research
facilities and promotes the design, development, and operation of
instruments and telescopes for astronomical research.
Founded
in 1839, Boston University is an internationally recognized
institution of higher education and research. With more than
30,000 students, it is the fourth largest independent university
in the United States. BU contains 17 colleges and schools along
with a number of multi-disciplinary centers and institutes which
are central to the school’s research and teaching mission.
GRS Press Release
Images
Principal Investigator: Dr. James Jackson
Images
and Captions compiled by Drs. Ronak Shah & Jill
Rathborne
March 2006
A
team of Boston University astronomers has produced the clearest
map to-date of the giant gas clouds in the Milky Way that serve
as the birthplaces of stars: the Galactic Ring Survey shown
at top. An expanded view of a large swath is included to
demonstrate the richness and detail seen by the GRS: the
densest, richest star forming regions are shown in white and red,
while the other areas contain more quiescent gas. The BU
team, along with colleagues from the University of Cologne
(Germany) and the University of Massachusetts, Amherst, spent
nearly a decade charting the gas using a radio telescope tuned to
a frequency of 110 GHz, which allowed them to trace a rare
isotope of carbon monoxide, 13CO, found within
molecular clouds. The advanced technologies of the
telescope allowed them to obtain a map of much finer detail than
previously possible. Furthermore, the choice of studying
the emission from 13CO, rather than the more common
12CO, allowed the team to peer more deeply into the
interiors of molecular clouds.
An
expanded view of the top most image, displaying the densest
condesations as well as filamentary structure of the molecular
clouds charted by the GRS.
A
blow-up of one region of intense star formation known as W51,
located at about 15,000 light-years from the Earth. W51 is
roughly 260 light-years, or nearly 16 million times the mean
Sun-Earth distance. The total amount of molecular gas
involved in the star formation process can be estimated using the
GRS data. For W51, the GRS team estimates that nearly
100,000 times the mass of the Sun's worth of material is taking
part in the formation of stars. Although it takes tens of
thousands of years to produce a new star, the GRS team estimates
that somewhere between 100 and 1000 stars are likely to form out
of W51. Most will be similar in mass to our own Sun, but a
small number will become behemoths, weighing in as much as 10
times the mass of our Sun. Such stars are probably located
deep in the bright region at lower left, and are responsible for
sculpting the wispy tendrils and sharp features through their
intense ultraviolet radiation found throughout W51. In
addition to the dense region of molecular gas in the lower left,
the GRS provides the contrast to view these faint, wispy tendrils
in the Milky Way's gas clouds. In fact, the GRS team
estimates that most of the molecular gas they charted is found in
less concentrated forms such as the wispy tendrils seen above.
Studying these less dense regions will allow the GRS team to
understand how molecular gas clouds assemble and produce stars
like those we see in the Milky Way.
A
molecular cloud referred to as the "backwards Nike swoosh",
showing a deep arch, located at about 12,000 light-years from the
Earth. Once considered unusual, such features are now
commonly found by the GRS team.
The vast quantity
of data acquired by GRS team requires them to carefully chose a
naming convention for individual molecular clouds. This
naming convention is typically based on a coordinate system quite
similar to Earth's latitude-longitude. The cloud at left,
for example, is properly termed GRS45.46+0.05; that's a lot
like referring to Boston, MA by its longitude and latitude (US
71° W+42°20' N, in case you were wondering). But
much like naming shapes from clouds in our own sky, astronomers
adapt pop-culture for the categorizing of the night sky, as
well. The GRS team generally refers to GRS45.46+0.05 as the
"Klingon" because of its strong similarity to an enemy
spaceship found in the Star Trek television series.
Not to be outdone by science fiction, the "Klingon", at
6.5 kpc, possesses some of the brightest, densest star forming
regions in the Galactic Ring Survey. Before the GRS, many
molecular clouds such as the Klingon were virtually unknown.
Now their impact on the Milky Way can be better
understood.
A
2°×1° region of the GRS displaying emission from
molecular clouds located within the Galactic Ring.
Previously identified as one of the most massive gravitational
structures in the Milky Way, astronomers believe that this
Galactic Ring is a signature feature of our home Galaxy: if alien
civilizations from other galaxies were to peer down on the Milky
Way, they would note the immense concentration of starforming
molecular clouds located in donut-like distribution about the
Galactic Center. The radius of this donut is estimated to
be about 15,000 light-years, about half the distance between the
Sun and Milky Way's center; it is also as thick as 3000
light-years in some places. The concentration of molecular
gas is spawning copious numbers of stars. An
interesting result obtained from studying such active regions of
star formation is that all of the molecular clouds studied so far
have similar lumpy structures, regardless of their size, mass,
and star-forming activity. These lumps will eventually
become stars and, according to the researchers, this similarity
suggests that all clouds form stars of various masses in roughly
the same proportion.
Source
/ Credit: Boston University
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