An Outburst For Reasons Unknown

This image from the Hubble Space Telescope shows V838 Mon, the bright red star in the center, and the aftermath of a sudden expansion in size and brightness. In fact, in 2002 when the star had this "outburst for reasons unknown", it suddenly became the brightest star in the Milky Way Galaxy. Then, just as suddenly, it faded. A "stellar flash" like this has never been seen before. Although it seems that this flash has expelled matter into space, the material that you see surrounding V838 Mon in the image is not material at all - it is a "light echo" travelling through the interstellar dust that already existed around the star cluster. The star is located about 20,000 light years away, and the light echo spans nearly 6 light years across.