V838 Monocerotis
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Nominated for most mysterious star in the Milky Way, V838 Monocerotis (abbreviated V838 Mon) briefly became one of the brightest stars in our galaxy. Its outburst began around January 1, 2002 and was discovered on January 6, 2002. It was initially thought to be a familiar type of classical nova, but astronomers quickly realized that instead, V838 Mon may be a totally new addition to the astronomical zoo. Observations have indicated that V838 Mon is a binary system where one of the stars somehow transformed itself over a period of months from a small under-luminous star a little hotter than the Sun, to a highly-luminous, cool supergiant star -- defying the conventional understanding of erupting stars and stellar life cycles.
V838_Mon_HST.jpg
In this spectacular image, one of a series recorded by the Hubble Space Telescope, the dimmed V838 Mon is surrounded by an "expanding" nebula. But the nebula is actually a series of light echoes from formerly unseen shells of dust up to light-years in diameter. Previously ejected, the intricate shells progressively reflect light as it reaches them from V838 Mon's outbursts. Astronomers anticipate that light echoes from farther out in the dust envelope will continue to be visible until about 2010. Some estimates now place V838 Mon about 20,000 light-years from planet Earth.
The shape of the light echo is far from spherical. For all points on the currently visible echo, the light has taken the same time to travel from V838 Mon to the dust and then to Earth. Thus the shape is of an extremely long ellipsoid; the illuminated part being almost parabolic with V838 Mon at its focus. The V838 Mon - dust - Earth path length is increasing at the speed of light, and the visible echo is simultaneously receding both from V838 Mon and from the Earth.
The designation V838 Monocerotis means "838th variable star of Monoceros (the Unicorn)".
External links
- Hubble Space Telescope press release (http://hubblesite.org/newscenter/newsdesk/archive/releases/2003/10/text/)
- An article about V838 Monocerotis published at Space.com (http://www.space.com/scienceastronomy/light_echo_030326.html)