Strangely glowing, floating dark clouds are silhouetted
against nearby bright stars in a busy star-forming region
viewed by NASA’s Hubble Space Telescope.

The image showing dense, opaque dust clouds — known as
globules — in the star-forming region IC 2944 is available
online at or or . It was taken by
Hubble’s Wide Field and Planetary Camera 2, designed and built
by NASA’s Jet Propulsion Laboratory, Pasadena, Calif.

Little is known about the origin and nature of these
globules in IC 2944, which were first found by astronomer A.D.
Thackeray in 1950. Globules are generally associated with
large hydrogen-emitting star-formation regions, which give off
the glowing light of hydrogen gas.

The largest globule in this image consists of two
separate clouds that gently overlap along our line of sight.
Each cloud is nearly 1.4 light-years along its longest
dimension. Collectively, they contain enough material to
equal more than 15 times the mass of our Sun. The surrounding
hydrogen-rich region, IC 2944, is filled with gas and dust
illuminated and heated by a loose cluster of stars that are
much hotter and more massive than our Sun. IC 2944 is
relatively close by, only 5,900 light-years away in the
constellation Centaurus.

Using the remarkable resolution of Hubble, astronomers
can for the first time study the intricate structure of these
globules. They appear to be heavily fractured, as if major
forces were tearing them apart. When radio astronomers
observed the faint hiss of molecules within the globules, they
realized that the globules are actually in constant, churning
motion, moving supersonically among each other. This may be
caused by powerful ultraviolet radiation from the luminous,
massive stars, which heat up hydrogen gas in the region. The
gas expands and streams against the globules, leading to their
destruction. Despite their serene appearance, the globules may
actually be likened to clumps of butter put into a red-hot

The globules are most likely dense clumps of gas and dust
that existed before the hot, massive stars were born. But once
the stars began to irradiate and destroy their surroundings,
the clumps became visible when their less dense surroundings
were eroded away. This exposed them to the full brunt of the
ultraviolet radiation and the expanding hydrogen-rich region.
The new images catch a glimpse of the process of destruction.

The hydrogen-emission image that clearly shows the
outline of the dark globules was taken with Hubble’s camera in
February 1999 by Bo Reipurth, University of Hawaii, Honolulu,
and collaborators. Additional broadband images that helped to
establish the true color of the stars in the field were taken
by the Hubble Heritage Team in February 2001. The composite
result is a four-color image.

The Space Telescope Science Institute is operated by the
Association of Universities for Research in Astronomy, Inc.,
for NASA under contract with the Goddard Space Flight Center,
Greenbelt, Md. The Hubble Space Telescope is a project of
international cooperation between the European Space Agency
and NASA. The California Institute of Technology in Pasadena
manages JPL for NASA.

Image Credit: NASA and The Hubble Heritage Team (STScI/AURA)
Acknowledgment: Bo Reipurth (University of Hawaii)

Thackeray's Globules in IC 2944
Thackeray’s Globules in IC 2944:
Strangely glowing dark clouds float serenely in this remarkable and beautiful image taken with the Hubble Space Telescope. These dense, opaque dust clouds — known as “globules” — are silhouetted against nearby bright stars in the busy star-forming region, IC 2944.

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Date Published: Thursday, January 03, 2002