Chandra peers into a nurturing cloud

Composite image. Credit: X-ray: NASA/CXC/PSU/L.Townsley
et al; Infrared: NASA/JPL-Caltech

In the context of space, the term ‘cloud’ can mean something
rather different from the fluffy white collections of water
in the sky or a way to store data or process information.
Giant molecular clouds are vast cosmic objects, composed
primarily of hydrogen molecules and helium atoms, where new
stars and planets are born. These clouds can contain more
mass than a million suns, and stretch across hundreds of
light years.

The giant molecular cloud known as W51 is one of the closest to
Earth at a distance of about 17,000 light years. Because of its
relative proximity, W51 provides astronomers with an excellent
opportunity to study how are forming in our Milky
Way galaxy.

A new composite image of W51 shows the high-energy output from
this stellar nursery, where X-rays from Chandra are colored
blue. In about 20 hours of Chandra exposure time, over 600
young stars were detected as point-like X-ray sources, and
diffuse X-ray emission from interstellar gas with a temperature
of a million degrees or more was also observed. Infrared light
observed with NASA’s Spitzer Space Telescope appears orange and
yellow-green and shows cool gas and stars surrounded by disks
of cool material.

W51 contains multiple clusters of young stars. The Chandra data
show that the X-ray sources in the field are found in small
clumps, with a clear concentration of more than 100 sources in
the central cluster, called G49.5−0.4 (pan over the image to
find this source.)

Chandra peers into a nurturing cloud

X-ray spectrum. Credit: Chandra X-ray Center

Although the W51 giant molecular cloud fills the entire
field-of-view of this image, there are large areas where
Chandra does not detect any diffuse, low energy X-rays from hot
interstellar gas. Presumably dense regions of cooler material
have displaced this hot gas or blocked X-rays from it.

One of the massive stars in W51 is a bright X-ray source that
is surrounded by a concentration of much fainter X-ray , as shown in a close-up view of the
Chandra image. This suggests that massive stars can form nearly
in isolation, with just a few lower mass stars rather than the
full set of hundreds that are expected in typical star
clusters.

Another young, massive cluster located near the center of W51
hosts a star system that produces an extraordinarily large
fraction of the highest energy X-rays detected by Chandra from
W51. Theories for X-ray emission from massive single stars
can’t explain this mystery, so it likely requires the close
interaction of two very young, . Such intense, energetic radiation
must change the chemistry of the molecules surrounding the star
system, presenting a hostile environment for planet formation.

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Credit: Chandra X-ray Center

A paper describing these results, led by Leisa Townsley (Penn
State), appeared in the July 14th 2014 issue of The
Astrophysical Journal Supplement Series and is available online.

NASA’s Marshall Space Flight Center in Huntsville, Alabama,
manages the Chandra program for NASA’s Science Mission
Directorate in Washington. The Smithsonian Astrophysical
Observatory in Cambridge, Massachusetts, controls Chandra’s
science and flight operations.

Explore further:

NGC 6357: Cosmic ‘winter’ wonderland

Journal reference:
Astrophysical Journal Supplement

Provided by: Chandra
X-ray Center