NASA image shows bright glare from a star Nasa has released an artist's impression, created using the Hubble Space Telescope, that appears to show a 'light echo' spotted by stargazers 11 years ago.In 2002 a previously unknown star stunned stargazers when it suddenly flared up to briefly become the brightest star in the sky.
The star, V838 Monocerotis, produced a stellar flash so brilliant that scientists had never seen anything like it before - then, just as suddenly, it faded.
A stellar flash like this was unprecedented because supernovas and novas typically expel matter out into space, often obscuring them from view.
According to Nasa, in a light echo, light from the flash is reflected by successively more distant rings in the complex array of ambient interstellar dust that already surrounded the star.
 It is still not known what caused the flare, but theories include an eruption caused by helium eruptions as the star entered its death throes, the swallowing of planets by V838 or that V838 is a very massive supergiant that underwent a thermonuclear event.
The expansion took only a couple of months, meaning that its speed was abnormal.
A paper with contributions from the US Naval Observatory, the University of Arizona and the European Space Agency concluded: 'When combined with the high luminosity and unusual outburst behavior, these characteristics indicate that V838 Mon represents a hitherto unknown type of stellar outburst, for which we have no completely satisfactory physical explanation.'
V838 Mon lies about 20,000 light years away toward the constellation of the unicorn (hence the name Monoceros), while the light echo in the image spans about six light years in diameter.
It appears that the star is considerably more massive and luminous than the Sun, perhaps five to ten times as big.