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.
About 700 light years away sits the expanding death cry of a star: the Helix Nebula, a four-light-year wide gas cloud blasted out when a star that was once like the Sun gave up its life.
A new image of it in colors just outside what the human eye can see shows just how much it does look like a screaming star:
[Click to ennebulenate, or download the huge 6600 x 600 pixel 35 Mb version.]
This image is in the near-infrared, taken using the European Southern Observatory’s Visible and Infrared Survey Telescope for Astronomy (VISTA), a 4.1 meter telescope in Chile. Equipped with a whopping 67 megapixel camera it can take pictures of large areas of the sky. The Helix nebula fits that bill: it’s close enough to us that it’s nearly the size of the full Moon in the sky.
This image is pretty nifty. It accentuates cooler gas than what we see in visible light. What’s colored red in the picture is actually infrared light coming from molecular hydrogen, and shows the sharp ring-like edge of the nebula. What you’re seeing here is not so much a ring as it is the walls of a barrel-like structure, and we happen to be seeing it nearly right down the tube (see Related posts below for all the info you could want on this amazing object).
It also accentuates the long, long streamers pointing directly away from the center. Those are comet-like tails coming from denser clumps of material boiling away as the fierce ultraviolet light of the central star floods out, their material flowing radially outward. This is seen in other nebulae as well.
And while it’s beautiful and scientifically very useful (I would’ve killed for data this nice when I was researching these nebulae in grad school), it’s also something of an existential reminder: someday, our own Sun will look a bit like this. Probably not quite this bright and well-defined; our local star doesn’t quite have the power needed to light up its surroundings this way. But for all intent and purpose, you’re seeing a snapshot of our solar system in seven or eight billion years.
Just in case you needed a little perspective this morning.
Image credit: ESO/VISTA/J. Emerson. Acknowledgment: Cambridge Astronomical Survey Unit
My love for planetary nebulae is on record. These expanding shells of gas from dying stars are really beautiful, and I find the physics of the way the gas is ejected to be fascinating. I’ve written about them a lot: check the Related Posts at the end of this article for links.
I like to observe them, too. In the summer there are quite a few that are easy targets, and one of the easiest to find is called M27, the Dumbbell. It’s in the constellation of Vulpecula (the fox), and is big and bright enough to spot easily in binoculars. I’ve probably seen it with my own eyes, no lie, hundreds of times.
But I’ve never seen it like this:
[Click to ennebulenate.]
Holy wow! That’s so cool! Literally: this is an infrared image taken by the Spitzer Space Telescope, showing it in light well beyond what our eyes can perceive.
That’s not at all how I’m used to seeing it! Read More