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Eta Carinae is famous because it is so immoderate -- the most extreme example of an unstable very massive star, lately recognized to be dramatically bipolar. Images and spectral data obtained with the HST have clarified some aspects of this star while opening difficult new questions.
Even the images of Eta Car made in HST's first year showed (1) a nearly symmetric pair of lobes in the ejecta; (2) qualitative differences between the front and back sides of these bipolar lobes; (3) ragged, large-scale equatorial debris. The old question of whether Eta is a binary system or a rapid rotator thus becomes more urgent, while the detailed dynamics of each lobe is now subject to realistic analysis.
FOS spectroscopy of Eta's core region less than 0.5" across, and images made with the FOC and PC, have begun to clarify the nature of "Weigelt's components", the objects close to the star that were discovered by speckle interferometry in the 1980's. However, this development inspires new questions about the gas and dust in that core region. The same spectroscopy, and also radio observations, have given us the first quasi-direct estimates of the present mass-loss rate of the star; this turns out to be "small" in the context of Eta Car but huge by conventional stellar standards.
