Annotated mosaic
Hidden behind a shroud of dust in the constellation Cygnus is a
stellar nursery called DR21, which is giving birth to some of the most
massive stars in our galaxy. Visible light images reveal no trace of this
interstellar cauldron because of heavy dust obscuration. In fact, visible
light is attenuated in DR21 by a factor of more than
10,000,000,000,000,000,000,000,000,000,000,000,000,000 (ten thousand
trillion heptillion).
New images from NASA's Spitzer Space Telescope allow us to peek
behind the cosmic veil and pinpoint one of the most massive natal stars
yet seen in our Milky Way galaxy. The never-before-seen star is 100,000
times as bright as the Sun. Also revealed for the first time is a
powerful outflow of hot gas emanating from this star and bursting through
a giant molecular cloud.
The colorful image (top panel) is a large-scale composite mosaic
assembled from data collected at a variety of different wavelengths.
Views at visible wavelengths appear blue, near-infrared light is depicted
as green, and mid-infrared data from the InfraRed Array Camera (IRAC)
aboard NASA's Spitzer Space Telescope is portrayed as red. The result
is a contrast between structures seen in visible light (blue) and those
observed in the infrared (yellow and red). A quick glance shows that most
of the action in this image is revealed to the unique eyes of Spitzer.
The image covers an area about two times that of a full moon.
Each of the constituent images is shown below the large mosaic. The
Digital Sky Survey (DSS) image (lower left) provides a familiar view of
deep space, with stars scattered around a dark field. The reddish hue is
from gas heated by foreground stars in this region. This fluorescence
fades away in the near-infrared Two-Micron All-Sky Survey (2MASS) image
(lower center), but other features start to appear through the obscuring
clouds of dust, now increasingly transparent. Many more stars are
discerned in this image because near-infrared light pierces through some
of the obscuration of the interstellar dust. Note that some stars seen as
very bright in the visible image are muted in the near-infrared image,
whereas other stars become more prominent. Embedded nebulae revealed in
the Spitzer image are only hinted at in this picture.
The Spitzer image (lower right) provides a vivid contrast to the
other component images, revealing star-forming complexes and large-scale
structures otherwise hidden from view. The Spitzer image is composed of
photographs obtained at four wavelengths: 3.6 microns (blue), 4.5 microns
(green), 5.8 microns (orange) and 8 microns (red). The brightest infrared
cloud near the top center corresponds to DR21, which presumably contains
a cluster of newly forming stars at a distance of nearly 10,000
light-years.
The red filaments stretching across the Spitzer image denote the
presence of polycyclic aromatic hydrocarbons. These organic molecules,
comprised of carbon and hydrogen, are excited by surrounding interstellar
radiation and become luminescent at wavelengths near 8 microns. The
complex pattern of filaments is caused by an intricate combination of
radiation pressure, gravity, and magnetic fields. The result is a
tapestry in which winds, outflows, and turbulence move and shape the
interstellar medium.