Intense radio outburst from the supermassive star η Carinae

Abstract

On five occasions between 1992 June 29 and 1994 May 3, we have used the Australia Telescope Compact Array to image η Carinae at a wavelength of 3 cm and a resolution of 1″. These observations have revealed remarkable activity. Since 1992 June, the total flux density has increase from 0.8 to 2.2 Jy, and the original single compact source has grown to a complex of sources spread over an area of about 16 arcsec 2 (Fig. 1). Strong hydrogen recombination-line spectral emission has appeared at the site of the strongest of these new sources. This recombination emission has the largest spectral width ever observed from a star, ± 250 km s'1, and reveals gas with turbulent velocities as great as 250 km s -1 approaching us at an average velocity of about 200 km s -1. We believe that this radio outburst has been caused by a more than threefold increase of ultraviolet luminosity, and consequent ionization of previously neutral gas clouds.