BZ Crucis

A distant star some 1,400 light years from the Solar System that shines in the southern parts of Crux as viewed from Earth. BZ Crucis lies on the bright band of the Milky Way, but between the star and Earth is a wide dark cloud known as the Coalsack. The light of BZ Crucis shines through the darkness of the Coalsack, making it the brightest point of light within this zone of darkness. This star lies in the same general field of the sky as the Coalsack Cluster, C98, and probably represents an outlying member of that cluster.

Physically BZ Crucis is a blue giant or subgiant shell star, periodically expelling material into a circumstellar disc of material. These periodic eruptions cause the star's brightness to fluctuate in a manner characteristic of Gamma Cassiopeiae variables (hence its designation 'BZ', which identifies the star as a variable). It is an unusually strong X-ray source, indicating that it belongs to a highly active system. The nature of this activity is not entirely clear: the star itself might have a remarkably active magnetic field, or there may be some other object in the system accreting material from the main star's shell.