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Hubble Space Telescope Observes Birth of Stars

By Kathy Sawyer
The Washington Post

The Hubble Space Telescope has detected embryonic stars emerging on the surfaces of monstrous pillars of interstellar gas, in images that astronomers say will rewrite the textbooks on theories of how a star is born.

The eerie pictures, released Thursday at a NASA briefing, reveal some 50 stellar embryos in the Eagle Nebula, 7,000 light years away. Normally hidden, the unborn stars are being stripped of their surrounding gas clouds by a barrage of ultraviolet radiation blazing from massive stars nearby.

Researchers have dubbed the finger-like tendrils within which the stars incubate EGGs (Evaporating Gaseous Globules.)

The images open a new window on the processes that create stars by the billions and fill the universe with light, astronomers said. It is the thermonuclear fires of stars that forge all the heavier elements in the cosmos, including the ingredients that make life possible.

The powerful radiation that stripped gas from around the EGGs also appears to have "frozen" the process of star formation. Because they have been cut off from the gas cloud that supplies their mass, some of the unborn stars can't grow big enough to trigger the thermonuclear fusion reactions required to make them shine.

"This puts the theory of how stars are born in a whole new light," said Stephen P. Maran, of NASA's Goddard Space Flight Center, a member of the Hubble science team. "It shows us that a star's big brother can dramatically affect whether or not the little guy gets formed and how big it is and can even put it to death."

"That's a new process. We've never seen that before," said Jeff Hester of Arizona State University, leader of the team that discovered the EGGs. "The first time we saw those data we were just blown away."

Astronomers have long disagreed about how nature determines the sizes of stars. Understanding that, said Bruce Margon, chairman of the astronomy department at the University of Washington, is "perhaps the biggest prize" in the science of star formation. The size, or mass, is the basis of all future properties such as how bright the star will be and how it will die. The new images, Margon said, offer the first "overwhelming evidence" of at least one process than can determine a star's size - erosion by radiation.

Only stars of a certain size can trigger thermonuclear fusion, which generates heat and light. If they are too large, they eventually collapse, and if they are not large enough, they stay too cold.

The Hubble findings show how to build a star - or a potential star - of almost any small size, researchers said. For example, they afford a long-sought explanation of how nature makes faint objects known as brown dwarfs-too small to shine like stars but too large to be considered planets. Some of the EGGs, in fact, could contain brown dwarfs, they said.

The Hubble images of the towering pillars, taken last April with the orbiting telescope's Wide Field/Planetary camera, remind some of monsters rising from the sea, others of stalagmites protruding from the floor of a cavern. The torrent of ultraviolet radiation from young stars nearby casts a ghostly light along the pillars' surfaces. The tallest pillar is about a light year long (5.8 trillion miles, or the distance light travels in a year) from base to tip, while each EGG is a bit larger than our own solar system, or about 100 billion miles across the tip.

The Eagle Nebula (also known as M16) is visible with binoculars between the constellations of Sagittarius and Serpens in the summer sky, but is currently low in the west at sundown. Scientists describe it as a blister on the side of a dense cloud of cold molecular hydrogen-the raw material from which stars form. Inside the blister, scientists using ground telescopes had detected the shine of about 100 newborn stars. The brightest of them are perhaps 100,000 times brighter than the sun, with temperatures of almost 90,000 degrees Fahrenheit.

At such temperatures, they emit their light at ultraviolet wavelengths, heating the surface of the molecular gas cloud and causing it to boil away into space-a process called photoevaporation. This process formed the columns of gas that protrude into the interior of the nebula. The columns had been seen through groundbased telescopes. But until the Hubble observations made last April, no one had seen the gas boiling off or observed that the erosion also exposes the star-bearing EGGs.

Although some astronomers had speculated about the impact of massive hot stars on their nearby siblings, "this is the first time we have actually seen the process of forming stars being uncovered by photoevaporation," Hester said.