I love a good coincidence. On Monday morning, I posted a gorgeous picture of the planetary nebula Abell 31, an object formed when a dying star blows off its outer layers in a series of winds which collide with each other. I mentioned that these nebulae are usually symmetric -- Abell 31 happens not to be because it's moving rapidly through space, and the gas through which it moves is compressing one side of it. But events like that are not the norm; most planetaries show stunning symetric features... like Henize 3-1333, as you can see in this nice Hubble image of it:
[Click to ennebulenate.]
It looks like a flower, doesn't it? The petals you see are actually sculpted lobes of gas. I'm guessing it undergoes periodic episodes where it blows out gas in focused beams, which then move outward and form those features as they plow into gas previously blown out by the star. It's a guess, but it fits what's known about the inner regions of the cloud near the central star. There's a thick disk of material surrounding the central star, something like 30 billion km (20 billion miles) across, far larger than our solar system. Every six years or so, the central star appears to dim, which may be due to the inner part of the disk itself becoming unstable and puffing up, blocking the light. This disk may also be responsible for shaping the outflow of the gas from the star, forming those petals.
If you're wondering just how much material the star is blowing out, it turns out to be about the mass of the Earth every year! That's a tiny fraction of the star's mass, but it blows out this much every year for thousands of years. Eventually that wind will turn off, and all that will be left is the very hot (30,000° C or about 55,000° F) core of the star, which will then cool over the next few billion years. Long before then the expanding gas around it will dissipate, and all that'll be left is a very diffuse cloud of material that will mix with the ethereally thin matter between the stars.
Well that, plus images like this one. And, of course, the knowledge we've gained studying how stars die.
Credit: ESA/Hubble & NASA