Fading Echo

Attending a conference in Northern Indiana has proven a little distracting, particularly since I’ve decided to prepare my talk using the LaTeX Beamer class instead of PowerPoint. It produces some handsome PDFs, but climbing the learning curve is a tad painful…

At any rate, that explains my fall back to astronomy. Haste. So it’s just another lovely image today, released as part of a Hubble Space Telescope announcement from ESA. If you have a chance, take a look at even the moderately higher-resolution image available online. The loops and whorls visible in the image above (or at least its higer-resolution counterpart) appear much more distinct than similar features in earlier images of the object.

You see, V838 Monocerotis isn’t like most nebulae—Orion and the Eagle, for example, glow because the gas inside them is heated up and ionized—instead, V838 glows by reflected light. Dust around the central star has been illuminated by an event that took place several years ago, a little like a flash going off in a darkened room, except that it takes years for light to traverse the extent of the surrounding material (thus, to continue the darkened room analogy, you’d need to think of the far wall of the room illuminated long after chairs, tables, or whatever in the foreground would be revealed by the flash). An earlier Hubble announcement about the object reveals V838 growing over time, not because the cloud itself is expanding, but because it has been lit by a burst of light that continues to wash over the dust that enshrouds the central source.

The nickname for this is a “light echo,” suggesting the bouncing of sound off increasingly distant hilltops. Sadly, like an echo, V838 will continue to grow dimmer over time (the intensity of light, after all, falls off as the square of the distance), so we should enjoy the fabulous images while we can.