In the mid-1800s, mariners sailing the southern seas navigated at night by a brilliant star in the constellation Carina. The star, named Eta Carinae, was the second brightest star in the sky for more than a decade. Those mariners could hardly have imagined that by the mid-1860s the brilliant orb would no longer be visible. Eta Carinae was enveloped by a cloud of dust ejected during a violent outburst.

Stars don't normally play vanishing acts unless they are undergoing rapid and violent activity. Observations by the Hubble Space Telescope and other observatories have helped astronomers piece together the story of this unique star's petulant behavior. During part of its adult life, Eta Carinae has undergone a series of eruptions, becoming extremely bright during each episode, before fading away. One explanation for the monster star's antics is that the convulsions were caused by a complex interplay of as many as three stars, all gravitationally bound in one system. The most massive member – weighing in at 150 times our Sun's mass – swallowed one of the stars. This violent event ignited the massive outburst of the mid-1800s. Evidence for that event, dubbed the Great Eruption, lies in the huge, expanding bipolar lobes of hot gas surrounding the system.

Because of Eta Carinae's violent history, astronomers have kept watch over its activities. Although Hubble has monitored the volatile superstar for 25 years, it still is uncovering new revelations. Using Hubble to map the ultraviolet-light glow of magnesium embedded in warm gas, astronomers were surprised to discover the gas in places they had not seen it before. The newly revealed gas is important for understanding how the eruption began, because it represents the fast and energetic ejection of material that may have been expelled by the star shortly before the expulsion of the bipolar bubbles.

One of the most massive known stars in the Milky Way galaxy, Eta Carinae is destined to finally meet its end by exploding as a supernova.

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