Cosmic Sculpture and the Joy of Not Knowing

Cosmic Sculpture and the Joy of Not Knowing

Adam Frank for McGraw-Hill

Most people think science is just about facts or just about knowing something. That is a sad misconception. Sometimes not knowing is the best thing that can happen to a scientist.

Stars like the sun don't die quietly. Before they start fading into the eternal night, a solar-type star will light off an extraordinary cosmic fireworks show called a Planetary Nebula (also called a PN). Planetary nebulae have nothing to do with planets. They are giant wispy clouds (almost a light year across) that looked vaguely like planets in the crude telescopes of astronomers who first discovered them. The name just stuck.

PN are special because they are big and easy to observe. That makes them good targets for anybody with a new telescope, including NASA. In the years since the Hubble Space Telescope was launched there have been so many startlingly beautiful PN images that I have lost count of them all. For astronomers like me who study PN, all that attention has been both a blessing and a curse.

Before the HST images became available, some of us foolishly thought we understood how PN formed. There were round PN, oval PN and even hour-glass shaped PN. All of this, we thought, presented no problem for our theories. We knew that all stars, including the sun, drive powerful winds from their surfaces and that those winds change as the star ages. We imagined that a star that makes a PN first belches a slow, dense wind into space. As the star got older, the wind changed, becoming tenuous but extremely fast (more than 1,000 miles per second!). Like a snowplow, the fast wind would plow into the slower moving gas ejected earlier and would sweep it into the bright shell we see as a round PN. If the nebula was oval or hourglass shaped that just meant that the slow wind got kicked off the star with a doughnut-like pattern (perhaps because the star was spinning rapidly). In that case the fast wind had to squeeze through the holes of the doughnut producing an oval or hourglass shaped PN shell. This "interacting stellar winds" theory was a nice, reasonable idea and for a long time it worked pretty well. Then along came the HST that showed us a lot of totally unreasonable nebulae.

In the sharp eyes of the Hubble, PN weren't just round, or oval or even hourglass shaped. In the new pictures there were arcs of gas that curved one way and then the other. Sometimes bright bullets appeared on either side of the star. Sometimes the bullets appeared in all different directions. The images were dazzling and bizarre and they took most of us by surprise. The old ideas just could not compete with the remarkable new data. We were baffled. That may seem like a sad situation for an astronomer to be in but, in fact, it's the opposite that is true. There is nothing more exciting for a scientist than not knowing what is going on. It's the best kind of vertigo because it forces you to break down your old ways of looking at things and try and see the whole problem anew. Have you ever tried to really shatter your old opinions about something? Have you ever tried to see the world in an entirely new way? It is not easy.

For the last five years astronomers like myself have been looking for a new way to explain how nature got to be so creative with PN. At one point I even laid the pictures out in front of my wife (who is a musician) and asked if she had any ideas. She liked the colors but couldn't point me in any useful directions. Since then I am happy to report that some new ideas have emerged. There are a series of new theories that explain the wild shapes of PN in terms of magnetic fields blown off by the dying star. These theories look promising but it is too early to tell yet if they will pan out. We are still, wonderfully, in the dark. We are still trying to see the problem anew. I will let you know if we hit something that really works but until then enjoy the pictures and recognize that that your guess may, quite literally, be as good as mine.