Behind a thick cocoon of cold gas, scientists have discovered what might be a new class of astronomical objects in our galaxy. Made up of a very massive star and a compact object such as a neutron star or a black hole, the binary system is unique because it remained hidden behind a cloud of obscuring material for so long. A paper describing the discovery will be published in Astronomy and Astrophysics in November.

The European Space Agency launched the Integral gamma-ray space telescope nearly a year ago. In January, it detected a previously undiscovered object, which astronomers dubbed IGR J16318-4848. Early analysis suggested it was similar to the 300 known combinations of compact objects and their companion stars in the Milky Way. IGR J16318-4848 was different, however, because it had eluded detection for so long. Using the XMM-Newton space observatory, the researchers detected a dense cocoon of cold gas surrounding the pair. The researchers posit that material ejected from the companion star, its so-called stellar wind, is accreted by the black hole to form a dense shell around the pair. The diameter of this thick cloud is roughly equivalent to the distance between the earth and the sun.

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