...a team is claiming the first direct evidence that Eta Carinae has a binary companion. Astronomers previously have been unable to detect this star for three reasons: the entire system is shrouded in vast quantities of dust, the secondary star's light is overwhelmed by the brilliance of the primary, and the two objects are separated by less than 10 milliarcseconds on the sky. Based on previous indirect evidence, many astronomers have long suspected that a companion lurks in Eta Carinae's midst. In 1997 Augusto Damineli (University of São Paulo, Brazil) first called attention to the fact that Eta Carinae's optical spectrum undergoes changes every 5.5 years, presumably due to an orbiting star swinging behind the primary star in an elliptical orbit. Subsequent X-ray observations have lent powerful support to this picture, indicating that the winds of the two stars violently collide when the two bodies approach each other every 5.5 years. But in a paper that has been posted on the Internet and that is scheduled to appear in the November 1st Astrophysical Journal, lead author Rosina C. Iping (Catholic University of America) and four colleagues report the direct detection of ultraviolet light from the companion.

Source: Sky and Telescope