One of the most amazing objects in the sky is the Helix Nebula, an expanding cloud of gas and dust surrounding a dying star. This type of object is called a planetary nebula, and it's formed when a star a bit more massive than the Sun turns into a red giant and blows off its outer layers. These expand away, and eventually the hot core of the star is exposed. This floods the gas with ultraviolet light, causing it to glow pretty much like a neon sign*. The Spitzer Space Telescope and GALEX combined their forces to observe the Helix Nebula, and what they see is simply stunning:
Oh my. [Click to ennebulenate, or grab a 6000 x 6000 pixel version.] GALEX sees in the ultraviolet, so it's sensitive to the light coming from the central star and the hot gas reacting to it (colored blue in the picture). Spitzer sees in the infrared, so it detects warm gas and dust (red, yellow, and green). Where you see pink is where the nebula is emitting both IR and UV. [Note: some of the outskirts of the nebula were beyond Spitzer's field of view, so images from the infrared observatory WISE were used there to match the GALEX field.] One of the most interesting features of this nebula is the collection of long, comet-like "fingers" you can see throughout the structure. These are where denser clumps of material are boiling away under the intense UV radiation of the central star, blowing out long tails away from the center like spokes in a wheel. Some of those tails are trillions of kilometers long! Despite being one of the closest planetary nebulae in the sky - a mere 700 light years away - I've never seen the Helix through a telescope. Why not? Because it's so big! The light from the gas is spread out over an area in the sky the size of the full Moon, dimming it considerably. Maybe someday I'll be at a dark site with a big 'scope, and I'll see this fantastic bauble with my own eyes... but it won't look like this picture. Our eyes see only a small slice of the electromagnetic spectrum. They serve us well in our daily lives, but the Universe itself sends out information in every direction to which we're blind. That is, until we used our limited brains to build devices like Spitzer and GALEX that expanded our viewpoint. And that's what science does: removes the scales from our eyes, allowing us to see what the cosmos itself is showing us. Image credit: NASA/JPL-Caltech
^* I'm simplifying here a bit. If you want more in-depth info on what happens as a star like this dies and glows like some great gaudy celestial Christmas ornament, read this post about the Helix I wrote a while back.
Related Posts: - Down the throat of a dying star - The Helix screams in the infrared - A warm anniversary for Spitzer - The Helix's dusty heart
