1. Astronomy Department, University of California, 601 Campbell Hall, Berkeley, California 94720-3411, USA

Correspondence to: Nathan Smith¹ Correspondence and requests for materials should be addressed to N.S. (Email: nathans@astro.berkeley.edu).

Very massive stars shed much of their mass in violent precursor eruptions¹ as luminous blue variables² (LBVs) before reaching their most likely end as supernovae, but the cause of LBV eruptions is unknown. The nineteenth-century eruption of Carinae, the prototype of these events³, ejected about 12 solar masses at speeds of 650 km s^-1, with a kinetic energy of almost 10⁵⁰ erg (ref. 4). Some faster material with speeds up to 1,000–2,000 km s^-1 had previously been reported^{5, 6, 7, 8} but its full distribution was unknown. Here I report observations of much faster material with speeds up to 3,500–6,000 km s^-1, reaching farther from the star than the fastest material in previous reports⁵. This fast material roughly doubles the kinetic energy of the nineteenth-century event and suggests that it released a blast wave now propagating ahead of the massive ejecta. As a result, Carinae's outer shell now mimics a low-energy supernova remnant. The eruption has usually been discussed in terms of an extreme wind driven by the star's luminosity^{2, 3, 9, 10}, but the fast material reported here indicates that it may have been powered by a deep-seated explosion rivalling a supernova, perhaps triggered by the pulsational pair instability¹¹. This may alter interpretations of similar events seen in other galaxies.

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