Protostars -- emerging stars -- in the star-forming
region of RCW49, in the Milky Way. Put your mouse over the picture
to see the star locations.Photos:
NASA / JPL / University
Shock may trigger star formation. When a massive, dying
star explodes in a supernova, the shock wave compresses clouds of gas
and dust, which start to collapse due to gravity. Over millions of
years, a new
wave of stars is born. Images: JPL/NASA
The lumpy knots in the arms of spiral galaxy Messier
81 are regions of intense star formation. The galaxy is 12 million
light years away, in the big dipper. Photo: NASA/JPL-Caltech/S.
Willner (Harvard-Smithsonian Center for Astrophysics)
Like a street vendor cranking out Beverly Hills star maps, astronomer Ed Churchwell makes maps of stars' homes. But his maps don't show you where Sylvester Stallone sulks or Eddie Murphy smirks; instead they show the location of starbirths.
Like the average Beverly Hills mansion, these star homes are concealed. But don't look for gates or guards. Instead, nascent stars are hidden from prying eyes behind giant hedges of interstellar dust -- tiny grains of silicon and hydrocarbons.
Now, looking in the infrared part of the electromagnetic spectrum with the Spitzer Space Telescope, Churchwell is watching stars form from clouds of hydrogen gas and dust in a part of the Milky Way poetically called RCW49. And while this area was already considered a star nursery, he's found hundreds of young stars, far more than expected.
In Hollywood, stars are made from a blend of talent, luck, and dark forces that cannot be detailed on a family website. In space, stars are made when giant clouds of cold gas and dust are compressed by gravity until they become dense enough to start nuclear fusion. Once hydrogen starts fusing into helium, stars release fusion energy for billions of years.
The giant birth-clouds are mainly hydrogen, with traces of simple compounds like carbon monoxide and ammonia. Temperature matters. "The clouds are within 10 to 15 degrees of absolute zero, they are very cold and quite dense," says Churchwell, a professor of astronomy at the University of Wisconsin-Madison. "When matter is this cold, it has almost no pressure, so naturally it wants to condense" due to gravitational pull between molecules.
But density is relative. A bucket of air has about 1,000,000,000,000,000 (10 to the 15th power) times as many particles as a bucket of star-spawning molecular cloud. Still, those clouds are supersize -- containing, say, 100,000 times the mass of our sun.
That, as they might say in Hollywood, is bigger than Star Wars!
Scientists think the clouds start condensing after being struck by a shock wave that raises gas density in some areas. Gravity then concentrates the gas, causing the formation of whirling "accretion disks" pregnant with stars. Because the clouds have some rotary motion, they rotate faster as they condense, just as a spinning skater draws her arms closer to her body.
For many years, astronomers wondered how the rotating mass could congeal at the center, since calculations showed that centrifugal force created by rotation would prevent the whirling material from reaching the center. It now appears that jets emerging from the poles of the developing star drain off enough rotational energy to allow condensation to happen.
The gas 'n dust that remains in the accretion disk plays an important supporting role in the production, Churchwell says. "We are pretty sure that planets formed from what was left over in the accretion disk, after the star, for whatever reason, says, 'I'm not gonna digest any more matter.'"
The infrared picture of RCW49 gives a new view of how much star formation is going on the in the Milky Way, says Churchwell. "Previously, astronomers had determined that the amount of star formation currently occurring in the galaxy is about 1 solar mass of material per year."
The formation of one sun each year, in a galaxy containing
about 100 billion stars, was nothing more than a walk-on role. But Churchwell
says, "I am betting that's way wrong. I suspect the amount of matter being converted is substantially higher." The
answer may come in a couple of years, after Churchwell's group finishes its
high-resolution, infrared survey of the Milky Way.
More new stars mean more accretion disks, and that means more planets -- and more auditions for the role of living creature...
But more star formation information will also illuminate the universe as a whole. As Churchwell observes, the universe is made of galaxies, and galaxies are made of ... you-guessed-it. "Most of the processes that are important to making galaxies what they are are really dependent on star formation, particularly massive star formation. We know that material in galaxies has to be mixed fairly often, and a lot of that is certainly due to the turbulent motions produced by jets from forming stars. They dump kinetic energy in the interstellar medium and stir up the clouds. All these processes are key to understanding the life and evolution of galaxies."
So when a bunch of stars come together in a galaxy, is it Oscar night?