What Happens When A Star Dies
“I was shocked,” recalls Arsen Hajian when he first saw this image of planetary nebula IC 418 in 1999. The astronomer, who now manages a company that develops imaging and spectroscopy equipment, picked the object for his postdoctoral research on measuring the distance to nebulae, because ground observations showed it to be round and featureless. “We took an image expecting it to be simple and straightforward; what we discovered was anything but,” he says. Hajian’s reaction was a common one among astronomers who were seeing the early images sent to Earth by the Hubble Space Telescope, especially in 1999, “the first time I could download Hubble data directly from the web page, as opposed to waiting for a tape to show up in the mail.”
A planetary nebula forms when a mid-size star, much like our sun, starts to die. The balance between the inward pull of gravity and the outward pressure from nuclear fusion shifts as the star’s hydrogen fuel runs out. When the star begins to collapse, the heat from this increased pressure ignites the helium, which “explodes like crazy compared to hydrogen,” Hajian explains. The force causes the star to “throw off its outer coat. Its atmosphere turns into a big puff of gas that rushes out into space,” reaching an area hundreds of times the size of our solar system. Meanwhile, with the new fuel expended, the core shrinks to about the size of Earth.
Astronomers used to believe most nebulae were simple, spherical objects, because they were imaging them with radio and ground-based optical telescopes, which could resolve only one or two pixels across. Now research is filled with the study of microstructures—the “little filaments and strands and blobs” that make up the wild nebulae we now know exist. “Hubble was really the driver behind that,” says Hajian.
The astronomer was mesmerized by the pattern that Hubble revealed on the surface of IC 418, which lies about 2,000 light-years from Earth. Hajian began to call it the Spirograph Nebula, “from when I was a kid, that little thing you put a pen in and twirl the little gear around and it makes a pretty picture.” Though Hajian suspects the pattern is created by some kind of magnetic effect, astronomers still haven’t pinned down the cause. If anything, Hubble has given astronomers as many new mysteries to solve as it has delivered answers.