Growing Eye

Credit: NASA, ESA, and H. Bond (STScI)

Before 2002, this “eye” in space went unno­ticed. The dim star under­went an out­burst that for a short time increased its bright­ness more than 600,000 times that of our Sun. Ever since the dra­matic bright­en­ing, astronomers have been turn­ing NASA’s Hub­ble Space Tele­scope back to watch a light show unfold.

Video: Unveil­ing of Light Echo around V838 Mon

In a series of images since 2002, astronomers have watched light echo off clouds of gas and dust sur­round­ing V838 Mono­cero­tis. A light echo is sim­i­lar to a sound echo, as if a yodeler lis­tened to their voice bounc­ing off nearby moun­tains. As light moved away from the star, it lit up objects far­ther and far­ther away, reveal­ing a mov­ing halo of light in the dust.

V838 Mono­cero­tis is an unusual vari­able star. Astronomers don’t under­stand what caused the star’s out­burst. Sci­en­tists described the bright­en­ing to be sim­i­lar to a nova. A nova occurs when a nor­mal star, like our Sun, dumps hydro­gen onto a smaller white-dwarf com­pan­ion star. Then like a bomb, it ignites. The tem­per­a­tures are so hot that nuclear fusion occurs; like a star-sized hydro­gen bomb. V838 Mono­cero­tis did not behave like a nova and dump its outer lay­ers. Instead it grew huge and its tem­per­a­ture dropped to that of a light-bulb. Per­haps this is a stage of a star’s life we have never seen. Astronomers also guess that the bright­en­ing could have been the result of a col­li­sion between two stars.

V383 Mono­cero­tis is found at the edge of the Milky Way Galaxy about 20,000 light-years from Earth toward the con­stel­la­tion Mono­c­eros, the unicorn.