As reported in Nature, the Hubble Space Telescope has captured some absolutely stunning photographs of the star V838 Mon as it went nova last year – or 20,000 years ago, depending on how you look at causality. Yet this was no ordinary nova. V838 Mon flashed to 600,000 times its previous brightness and for a brief time was the brightest star in the Milky Way galaxy. Yet the star did not expel its outer layers of gas like an ordinary nova, which produces temperatures of hundreds of thoushands of degrees. This star grew in size enormously without expelling gas while its surface temperature dropped to a level not much hotter than a light bulb. Growing so large without losing the outer layers is very unusual and completely unlike an ordinary nova explosion. “We don’t know what has caused this to happen,” said astronomer Sumner Starrfield of Arizona State University. “This object got bigger and brighter and cooler, but we don’t know why. Right now we know the effects and we’re trying to use the effects to determine the cause.”
“At this point, we can only say that we know of two sources that could release so much energy so quickly: gravitational energy, or thermonuclear energy,” says Howard Bond of the Space Telescope Science Institute in Maryland. “Gravitational energy, such as in a stellar collision or merger, seems unlikely because the surrounding circumstellar dust suggests that V838 Mon has undergone previous outbursts – a stellar interaction would be a one-time event. We may be seeing the release of energy through nuclear fusion, but in a region of parameter space that we have not seen before.”
Adding to the star’s beauty is a somewhat rare phenomenon called a light echo. This effect can appear to travel faster than the speed of light, but is really just an illusion. As the light from the outburst spread into space, it reflected from surrounding rings of dust to reveal a spectacular, multicolored bull’s eye that is now 3 light years across and still growing. Researchers believe that the light echo will be observable through the next decade, and they plan to use the time to make measurements with an array of space- and ground-based telescopes. “This research will likely have significant impact on our understanding of the late phases of stellar evolution,” said Phil Ianna of the National Science Foundation. “Once again we see how the collaborative efforts of researchers combining space-based and ground-based data reveal details about objects not even imagined before.”