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> Open cluster Westerlund 1 in Ara
Open cluster Westerlund 1 in Ara
author: ESO/Novapix
reference: a-aou98-00300
Image Size 300 DPI: 35 * 22 cm
This exceptionally bright cluster lies about 16 000 light-years from Earth in the southern constellation of Ara (The Altar). It contains hundreds of very massive and brilliant stars, all of which are just a few million years old — babies by stellar standards. But our view of this cluster is hampered by gas and dust that prevents most of the visible light from the cluster's stars from getting to Earth.
Around one of the stars — known as W26, a red supergiant and possibly the biggest star known— astronomers have discovered clouds of glowing hydrogen gas, shown as green features in this new image.
Such glowing clouds around massive stars are very rare, and are even rarer around a red supergiant— this is the first ionised nebula discovered around such a star. W26 itself would be too cool to make the gas glow; the astronomers speculate that the source of the ionising radiation may be either hot blue stars elsewhere in the cluster, or possibly a fainter, but much hotter, companion star to W26. W26 will eventually explode as a supernova. The nebula that surrounds it is very similar to the nebula surrounding SN1987A, the remnants of a star that went supernova in 1987
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