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Stellar astronomy

Clocks within the hourglass

Nature volume 390, pages 555–556 (1997)Cite this article

Rarely in astronomy can a stellar cataclysm be predicted in advance. It is also rare that an extremely well-studied object suddenly reveals a previously undetected periodicity. But both of these things are true for one of the most famous stars in the sky, the luminous blue variable Eta Carinae. On page 587of this issue1, Corcoran et al.report the discovery of small-scale X-ray outbursts from this source, which repeat every 85 days, superimposed on an overall increase in the mean X-ray flux, which may herald a dramatic ‘event’ in January.

Luminous blue variables (LBVs) represent a short-lived phase in the evolution of massive stars, during which the star occasionally erupts, changing markedly in its brightness and spectrum. The variations typically fall into three categories: ‘micro’ variations, up to a few tenths of a magnitude (one magnitude is a factor of about 2.5) on timescales of weeks to months; minor eruptions (increases in brightness by about one magnitude on timescales of years); and giant outbursts (increases by more than three magnitudes, with durations of decades2). LBVs may be an evolutionary stage between massive ‘O-type’ stars that are still burning hydrogen in their cores, and Wolf-Rayet stars, which have run out of hydrogen and must burn helium instead.

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Figure 1: Eta Carinae, a century and a half after its last giant eruption.

HST

References

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Authors and Affiliations

  1. the Space Telescope Science Institute, Baltimore, 3700 21218, San Martin Drive, Maryland, USA

    Mario Livio

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  1. Mario Livio
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Livio, M. Clocks within the hourglass. Nature 390, 555–556 (1997). https://doi.org/10.1038/37478

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