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V838 Monocerotis (V838 Mon) is a red variable star in the constellation Monoceros about 20000 light years (6 kpc) from the Sun, and possibly one of the largest known stars. The previously unknown star was observed in early 2002 experiencing a major outburst. Originally believed to be a typical nova eruption, it was then realized to be something completely different. The reason for the outburst is still uncertain, but several conjectures have been put forward, including an eruption related to stellar death processes and a merger of a binary star or planets.
This 2005 Hubble image of V838 Mon reveals dramatic changes in the illumination of surrounding dusty cloud structures. The effect, called a light echo, has been unveiling never-before-seen dust patterns ever since the star suddenly brightened for several weeks in 2002.
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Credit: NASA, ESA, and The Hubble Heritage Team (AURA/STScI)
Image enhancement: Jean-Baptiste Faure