APOD - Light Echoes

Light Echoes from V838 Mon - APOD
Image Credit: NASA, ESA, H. E. Bond (STScI)

A light echo is the visual analog of a sound echo and the Hubble image above shows the apparent brilliant burst of light from V838 Monocerotis, a red variable star in the constellation Monoceros (Greek for Unicorn). This star exploded for uncertain reasons, but the magnitude of the light burst is due to light reflected by the more distant rings of interstellar dust already surrounding the star. Because of these light echoes, the rate of expansion of this explosion appeared to be superluminal (faster than the speed of light). The rapid expansion can be viewed in the image below. A sound echo is something we instinctively understand, but picturing light echoes is another thing altogether, since we don't experience it in our lives.  The starburst in Monoceros, observed in 2002, is a beautiful, cottony mass of light, color, and dust - and still a mystery.


Successive photos of V838 Monocerotis showing the progress of a light echo.