Energetic star becomes a cool supergiant Mar 27, 2003 When a
star in the constellation of Monoceros, or the “Unicorn”,
erupted in January last year, it temporarily became the
brightest star in the Milky Way. Howard Bond of the Space
Telescope Science Institute in Maryland and astronomers in the
US, the Canary Islands and Italy have now used the Hubble Space
Telescope to study the light emitted by the star, known as V838
Monocerotis. Their work is significant in that it provides a new
method for measuring how far away stars are (H E Bond et al.
2003 Nature 422 405). Novae and supernovae usually undergo
explosive outbursts that eject stellar material into space. When
V838 Mon erupted, it brightened by a factor of 10 000 and so led
astronomers to believe that it was a classical nova. However,
the star did not eject its outer layers and expose a hot core –
unlike a conventional nova - but simply expanded to become a
cool, luminous supergiant instead. This transformation defies
the conventional understanding of th