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So, from starbirth we get stardeath. That follows, sure as...um... death and taxes. These things move in cycles. Starbirth regions almost always have some elements created by the deaths of the stars that went before them. Much as dying vegetable matter seeds a field here on Earth with the essential nutrients for the next generation of plants and animals, old stars recycle themselves into interstellar space. The elements they leave behind—carbon, nitrogen, oxygen, on up to silver, gold, and iron, and even the radioactive elements like thorium and uranium—get re-used in newborn stars and planets. It's a pretty efficient mechanism for the universe to re-create itself through the billions of years it has existed, and it will continue for as long as there are stars to give off material.
Of course, the most famous stardeath sites are supernovae, particularly the kind known as Type 1a, which occur when massive stars explode and hurl their outer layers to interstellar space.
There are other ways for stars to die and pass on their "legacy" of elements to the cosmos. The Sun won't die as a supernova, but it will swell up to become a red giant. Much of its mass will get blown off to space, and THAT mass will also be recycled into new stars a few billions of years from now. There's evidence that material from several dying stars provided the seed material for the Sun and planets, which puts us and our home world smack in the middle of the cosmic cycle of life and death.
Planetary nebula M2-9, from Hubble Space Telescope. Could our own Sun look like this, four or five billion years from now? It's destined to become a planetary nebula, pushing its atmosphere out to space as it dies.
Regions of stardeath are nearly everywhere we look in our own galaxy and in countless other galaxies, too. They look remarkably similar, a testament to how the laws of physics and astrophysics work across time and space.
Since it's snowing like mad and the wind is blowing like a banshee here (and the temperature is a toasty 21 degrees Fahrenheit) right now, I want to talk about hot stars. Specifically, let's talk about hot, dying stars that were once like the Sun. Here's NGC 2440 to help me take my mind off the cold weather! (For you folks in sunnier climes, count your blessings!)
So, NGC 2440 first came to my attention back when I was working on my first book with Jack Brandt, called Hubble Vision. We wanted to show a nice array of stars at different stages in their lives. Star lives, by the way, are way longer than ours, but like us, they proceed in stages. There's the infancy part—that takes place in a cocoon of gas and dust. Then, there's the "living" part, where the star consumes nuclear fuel in its core for some amount of time. Then, there's the old age part, where the star starts to lose mass in huge quantities and finally gives up the ghost. If the star is massive (like more than 8 or 10 times the mass of the Sun), then it sheds lots of its atmosphere before blowing itself to smithereens in a supernova explosion.
If the star is like the Sun, then it litters its environment with material that it blows away from itself. It does it maybe once, or maybe several times, creating shells of gas (nitrogen, hydrogen, oxygen, and helium, for example). That "exhaled" matter forms a shell around the star. Then, the interior star contracts (shrinks), and in the process, heats up.
So, NGC 2440 (what's left of it) is very hot—like 400,000 degrees Fahrenheit (try more than 400,000 times hotter than your oven gets). All that heat has to go somewhere and do something, so it's lighting up the huge cloud of mass that the star lost earlier in its life.
There was more than one outburst from NGC 2440 during its old age, which is why we see two "lobes" of material surrounding the central star.
If you want to see a huge version of the image above, go here (the HST news center). The highest-resolution image almost looks three-dimensional.
This is one of the neatest visions of the Helix Nebula (a planetary nebula) that I've ever seen. It's from the Spitzer Space Telescope, which looked at this remnant of a dying, Sun-like star in infrared wavelengths of light at 3.6-4.6 microns, 5.8-9 microns, and 24 microns (in blue, green, and red, respectively).
So, this image is a snapshot of various events that happened as the star's death progressed. First, the green-blue shell is the infrared view of the first layers of gas blown off as the star began its death throes. They've traveled the farthest from the star. The reddish diffuse shell just inside the blue-green clouds is dust that was kicked up when the outrushing atmosphere collided with dusty comets that survived the death of the star. The comets survived the first pulse of outgassing from the star, which is a rare occurrence. As events unfolded, the cometary ices melted away, leaving behind clouds of dust to bounce around in the swirling, outrushing gas. The red ball in the center is a shell of gas that was blown away from the star as it died. And, the white dot in the center (go here to see a larger image) is what remains of the Sun-like star.
People always ask what will happen with the Sun dies. Well, it might just look like this more than 5 billion years from now!
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