What does the echo of light look like? Nasa image shows the aftermath of the moment one star shone brighter than any other in the sky
- Hubble Space Telescope images show the 'light echo' from the unprecedented flare-up of a star
- Although theories abound, it is not yet known what caused the million times solar luminosity event
- Light from the flash is reflected by interstellar dust
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.
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Poetry of heaven: Nasa has released an image of the 'light echo' produced by the glare from a star that was, for one brief shining moment, the brightest in the night sky
WHAT IS A 'LIGHT ECHO'?
It is light from a stellar explosion echoing off dust surrounding the star.
V838 Monocerotis produced enough energy in a brief flash to illuminate surrounding dust, like a spelunker taking a flash picture of the walls of an undiscovered cavern.
The star presumably ejected the illuminated dust shells in previous outbursts.
Light from the latest outburst travels to the dust and then is reflected to Earth.
Because of this indirect path, the light arrives at Earth months after light from the star that traveled directly toward Earth.
Now Nasa has released an artist's impression, created using the Hubble Space Telescope, that appears to show V838 expel material into space, but what we are actually seeing is an outwardly moving 'light echo' of the bright flash - about a million times solar luminosity - from 11 years ago.
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.
V838's light echo expanding over time: It produced a stellar flash so brilliant that scientists had never seen anything like it before