Discovery of a massive equatorial torus in the eta Carinae stellar system

The enigmatic object eta Carinae is believed to represent an important, but short-lived, unstable phase in the life of the most massive stars, occurri ng shortly before they explode as supernovae or collapse directly to black holes. The putative binary(1,2) system believed to constitute eta Carinae s urvived an outburst in the previous century that lasted 20 years; and which created a nebula with pronounced bipolar lobes that together contain about 2.5 solar masses of material. The nebula also exhibits an equatorial 'wais t' containing about 0.5 solar masses(3). The physical mechanisms responsibl e for the outburst and the bipolar geometry are not understood. Here we rep ort infrared observations (spectroscopy and imaging) that reveal the presen ce of about 15 solar masses of material, located in an equatorial torus. Th e massive torus may have been created through highly non-conservative mass transfer, which removed the entire envelope of one of the stars, leaving an unstable core that erupted in the nineteenth century. The collision of the erupted material with the pre-existing torus provides a natural explanatio n for the bipolar shape of the nebula.