Astronomy

A Celestial X-ray Mirror

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Science  15 Feb 2013:
Vol. 339, Issue 6121, pp. 738-739
DOI: 10.1126/science.339.6121.738-d
CREDIT: M. L. MCCOLLOUGH, R. K. SMITH, L.A. VALENCIC, THE ASTROPHYSICAL JOURNAL 762, 2 (1 JANUARY 2013) © 2013 THE AMERICAN ASTRONOMICAL SOCIETY. REPRODUCED BY PERMISSION OF AAS

Bok globules, named after astronomer Bart Bok, are dense clouds of cold gas and dust that are usually condensing to form one or more stars. They are so dense that they can be totally opaque to visible light, often appearing in optical images as dark patches against the bright stellar background. McCollough et al. report a Bok globule that scatters the x-ray light emitted by a nearby binary system and thus appears as an x-ray emission feature in data taken with NASA's Chandra x-ray Observatory. The binary system, Cygnus X-3, is a powerful x-ray source located in the plane of our galaxy, where a massive, evolved star and either a black hole or neutron star orbit around their common center of mass. The x-ray data show an extended emission region associated with Cygnus X-3 that varies in flux and orbital phase with the binary. This behavior is best explained as the result of scattering from a cloud located between Cygnus X-3 and the observer, which acts as an x-ray mirror to Cygnus X-3. The cloud's size, density, and mass, derived from the x-ray data, are consistent with those of a Bok globule.

Astrophys. J. 762, 2 (2013).

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