The nozzles themselves are hidden in the nebula’s bright central blob of light. Whatever things are creating the jets, they are too small for even Hubble to pick out. Debate rages as to their nature. One possibility is that the central star is really two stars, one sucking an equatorial disk of matter out of the other, perhaps a white dwarf stealing from a distended red giant. As the space around the equator grows overcrowded, other stuff spewed by the dying giant would tend to get funneled into jets along the polar axis. Another possibility is that the central star has a powerful magnetic field that twists up into polar funnels as the star’s interior gurgles to the surface and becomes exposed. Combinations of the two mechanisms are also possible.

Abell 39 is an ancient planetary nebula that has been spreading out for thousands of years. It now stretches six light-years across. Whatever violence it knew in its early years is long forgotten. The cloud is so diffuse that distant galaxies can be seen through it. Astronomers once would have called the orderly, spherical Abell 39 a textbook example of a planetary nebula-but the Hubble Space Telescope has forced scientists to rewrite the textbooks.

Courtesy of WIYN/NOAO/NSF

To O’Dell, who has been observing planetary nebulas for more than 40 years, all those beautiful shapes are a confounding diversion. “They’re overly fascinating,” he says. “They have such a wealth of detail. We can hope to understand the gross features, but the better we observe them, the more it seems there is an endless series of finer and finer problems. The challenge becomes to distinguish the important ones.” He admits to being fascinated by the fine, comet-shaped knots recently observed inside the Helix nebula-they are clumps of molecular gas that escaped being ionized by the star’s ultraviolet blast-but only because they relate to the big picture. Those blobs of dead star stuff may survive intact and become a part of the next generation of stars. “It’s an ecological situation,” O’Dell says.


Courtesy of NASA/Hubble/STScI 

Courtesy of NASA/NOA/Hubble/STScI/NRAO

Courtesy of NASA/NOA/Hubble/STScI/NRAO

The Helix nebula (top), so near Earth it can be seen with binoculars, shows a late stage in the evolution of the cometlike knots present in some planetary nebulas. The knots, clearly shown in the Hubble close-ups (bottom left and right), are clumps of dust and molecular gas so dense that energetic radiation from the star swept by without shredding them. A typical one is larger than our solar system and weighs as much as Earth. “What we’re trying to figure out is whether they will survive,” says astronomer C. Robert O’Dell. If they do, the knots would most likely become a part of a very different kind of nebula, called a giant molecular cloud, that will eventually give birth to a new generation of stars.

Ecology is important, but so are the lives of individuals. The big picture is important, but so are the details. In stellar affairs, as in human ones, they help make the big picture interesting. The planetary nebula that Miranda has been observing, K3-35, may or may not reveal a general principle of star death-but he calculates that it was born no more than 20 years ago. In planetary nebulas, the timescale of astronomical moments intersects with the timescale of human ones. “Probably these jets will disappear in my lifetime,” says Imai, who is 32, talking about W43A, which could become a planetary nebula any day now. “If we don’t continue to observe it, we will miss that special moment.”