The supernova that wasn't.

In 1954, astronomers witnessed the brilliant outburst of a star in a nearby galaxy. The discoverers dubbed the object Variable 12, but for decades it remained unclear whether the star had survived the eruption. Many researchers concluded that the outburst, which came to be known as supernova 1954J, had indeed demolished the star.

But some astronomers, notably Roberta M. Humphreys of the University of Minnesota in Minneapolis, were not so quick to write off the star. They maintained that SN 1954J was a supernova imposter. It had undergone a violent phase that sometimes occurs in the evolution of a very massive star and that resembles a supernova explosion but leaves the star intact.

During the 1990s, Humphreys and her colleagues used a telescope at Lowell Observatory in Flagstaff, Ariz., to record a fuzzy, faint patch of light at the same position as Variable 12. They argued that it represented the erupting star, now in a quiescent phase. However, the images were too blurry to be completely convincing.

Last year, Schuyler D. Van Dyk of the California Institute of Technology in Pasadena and his colleagues used the Hubble Space Telescope to resolve the fuzzy patch into four stars. One of them is almost certainly the survivor of the outburst observed in 1954, Van Dyk says. This star has the color and brightness of an aging, very massive star. Furthermore, it is swathed in a dusty, gas-rich shell similar to the shell encasing the massive Milky Way star Eta Carinae, a well-known survivor of several severe eruptions. Finally, spectra taken with the Keck Observatory on Hawaii's Manna Kea show that the shell of the suspected survivor is rapidly expanding into space, just as the shell of Eta Carinae is.

All these lines of evidence, says Humphreys, confirm that Variable 12 is indeed a supernova imposter that survived the 1954 eruption.--R.C.