Star Nurseries

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A new star is born every year in our galaxy. New year, new star — that's the average. From wombs of dark, cold dust and gas, these overwhelmingly big and dazzling orbs burst forth to light up the Milky Way.

Breathtaking portraits of blooming stars in their strange nurseries have proved to be a specialty of the Hubble Space Telescope, orbiting high above the planet Earth. Among the most stunning so far is a picture of a star cluster called, unprettily, NGC 3603.

In this one shot, the telescope captured three stages in star gestation, as well as a violent gang of middle-aged stars, and one oldster, on the brink of catastrophic death. The picture was an accident, naturally.

"That star with the ring, that's what we wanted a picture of," laughs You-Hua Chu, a University of Illinois astronomer on the team that requested the photo. The team aimed for star death, and got the whole life story.

Oddly, the story of our own humble star, our sun, could never unfold in this particular nursery, which is dominated by violent giants. "Oh, no, no, no. No solar system. It's too stormy," says Chu. "Maybe in the darkest corner ... No," she concludes, "it would be hard."

In spite of the storm, however, stars are gestating in the giant galactic nebula NGC 3603. One safe spot is towering pillars of gas that have withstood the star cluster's gale of radiation, a byproduct of the nuclear fusion that makes stars shine. While the storm rages outside, deep inside the pillars, gas and dust may cool and condense into thick clots. These can collapse to form stars.

A second source of new stars in the nebula are dense, onion-layered clouds of gas and dust called Bok globules. If a Bok globule's outer layers of dust manage to shield the interior by absorbing the radiation blizzard, then its protected inner layers can cool to about -441 degrees F. Even as this cooling gas and dust churns at supersonic speed, it settles toward the center, or "centers." One globule can hatch more than one star.

Here's how: Deep inside a globule, a dense core of cold gas and dust will form. The strengthening gravity of that core will attract additional gas and dust. Eventually, the core will collapse under its own weight, becoming a massive, spinning ball. A small "protostar" is conceived.

If this star is to bloom, it must gather more fuel quickly, before the radiation blizzard breaks through the wall of its protective globule.

Each fledgling star will continue gathering fuel, until it is so heavy and hot that its hydrogen atoms begin fusing together and shedding radiation: A star is born.

The gas and dust remaining within the star's gravitational reach will gradually flatten into a "protoplanetary disk," or proplyd, circling the star's equator.

Normally, this disk would coagulate into pebbles and boulders and comets and asteroids and planets. But in this rough neighborhood, radiation will soon evaporate the disk, leaving a naked, new star.

Clustered in NGC 3603 is the galaxy's greatest collection of huge, violent stars. At least 10 are 100 times the size of our sun, and perhaps 10,000 more are sun-sized. "How can so many stars form in such a small volume?" Chu asks. "It's something people don't understand."

A howling blizzard of radiation and stellar wind blows out from the cluster, clearing a vast, dark hole in yellow-tinted gas and dust around the giant stars. Among the middle-aged stars in this cluster, the small ones will blaze for 10 billion years. The giants will explode after just a few million.

Though the enormous stars in the central cluster are bullies today, this is their fate. After only a few million years of shining, they will have burned so much of their fuel that they'll begin to go haywire.

Sher 25, the brightest star seen in the image of NGC 3603, is taking a novel approach to death. Its throes have already resulted in a ring around its equator, and a balloon-shaped bubble of gas that's expanding over each pole.

"I wish someone would study it!" Chu says. "It's gonna explode! Maybe not in my lifetime, but soon!"

When Sher 25 does go supernova, its ejected shells of old gas will tear outward at thousands of miles per second. Like snowplows, each piece of this shattered star shell will gather up the thin gases of space, packing together a new gas clot. And as each cools, some of the gas will condense into dust. The protective dust will allow the gas to cool further.

And new, pregnant clots will set about the business of growing fresh stars.