The Stingray Nebula and XKCD
> “There, peeping among the cloud-wrack above a dark tor high up in the mountains, Sam saw a white star twinkle for a while. The beauty of it smote his heart, as he looked up out of the forsaken land, and hope returned to him. For like a shaft, clear and cold, the thought pierced him that in the end the Shadow was only a small and passing thing: there was light and high beauty for ever beyond its reach.” -J.R.R. Tolkien
But over at XKCD, that quote provides little comfort. After all, “for ever” isn’t exactly quite right.
Even the stars must all exhaust their fuel and die.
Right?
Let’s head on over to the Constellation Ara, down in the Southern Hemisphere.
Looking close-up at one spot in the sky, you can find a very special star, known to astronomers as Hen 3-1357.
(Image credit: Kent Wallace.)
Throughout most of recorded history, it was a star similar to our Sun, only a little more massive — maybe two or three times as heavy — and it was headed towards the end of its life.
You see, when a star like the Sun puts out energy, it does so by fusing light elements into heavier ones in its core.
When it runs out of the lightest element, Hydrogen, it starts fusing the next lightest element, Helium, into still heavier ones. And it will keep doing this — if you can generate enough pressure and temperature — all the way up until it fuses elements into iron, the most stable of all the elements.
Towards the end of its life, the star becomes a red giant, swelling to many times its normal size.
The best known red giant, actually, is your friend Mira, which isn’t just a red giant, but is a special type of red giant that lives on the asymptotic giant branch.
These stars, more massive than our Sun (but not so massive that they’ll go supernova), actually pulse, and start to blow off their outer layers, which expand incredibly fast and cool down, forming a protoplanetary nebula.
(Image: the Egg nebula, a protoplanetary nebula imaged by Hubble.)
And then it happens. That last bit of burnable fuel gets used up, and that’s the end of your star!
Well, kind of. The core of the star contracts, and forms a white dwarf, releasing a large amount of energy. The outer layers get permanently blown off, and create a planetary nebula that gets lit up by the energy released from the inner core’s contraction.
This “moment of death” of the star in Ara occurred in 1987, and formed the Stingray Nebula.
(Image credit: Hubble space telescope, 1996.)
Looking at the very interior, we can actually see that there are two stars; this is a binary star system!
But what’s going on at the outside is by far more interesting. This object is way smaller than every other planetary nebula we know about; it’s only a few percent of a normal nebula’s size!
But you see those “blips” on either side? That look like something is starting to blow the gas outward? That’s a glimpse into the future of what this planetary nebula is going to look like!
Rather than a perfectly symmetric nebula, we’re likely to wind up with something with a definite preferred axis. Maybe it’ll be extreme, like the Boomerang Nebula?
Or maybe it will be a beautiful, intricate pattern lengthened in one direction, like the most photogenic of nebulae, the Cat’s Eye Nebula?
(Last two images by Hubble, of course!)
Regardless, this isn’t so much a death as a transformation. Your 15th magnitude Red Giant from the Asymptotic Giant Branch isn’t gone so much as it’s blowing off its outer layers and evolving into a white dwarf.
Kind of similar to…
…a caterpillar morphing into a butterfly!
So it isn’t really “death” at all, it’s simply the next stage of this star’s life cycle. And if we started with Lord of the Rings, it’s only fitting to end it the same way.
> Pippin: I didn’t think it would end this way. Gandalf: End? No, the journey doesn’t end here. Death is just another path, one that we all must take. The grey rain-curtain of this world rolls back, and all turns to silver glass, and then you see it. Pippin: What? Gandalf? See what? Gandalf: White shores, and beyond, a far green country under a swift sunrise. Pippin: Well, that isn’t so bad. Gandalf: No. No, it isn’t.
This is going to change quickly, so let’s make sure to look back in a few years, and see what the Stingray Nebula becomes!
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URL: http://scienceblogs.com/startswithabang/2011/01/the_stingray_nebula_and_xkcd.php