Beth Wohlberg
Daily Camera
November 13, 2000

New pictures of the youngest stars ever seen are expected to help scientists better understand how stars are born.

Two University of Colorado professors, working as part of a team of international researchers, used the Chandra X-ray telescope in space to observe almost 40 baby stars in the Orion constellation.

They found that baby stars, or protostars, are very violent, spewing extremely hot plasma over an area about one hundred times bigger than the sun.

The observations were announced Thursday at a meeting of the High Energy Astrophysics Division of the American Astronomical Society in Honolulu, Hawaii. In addition to the professors from CU's Center for Astrophysics and Space Astronomy, members of the international team of researchers are from Japan's Kyoto University and Penn State University.

"In the last 100 years, we learned how stars evolved and how they die, but one outstanding problem is how stars are born," said CU astronomy professor Bo Reipurth, who was part of the five-member team. "It gives us a new piece of the puzzle about how stars are formed."

The baby stars observed by the researchers are about 1,500 light years away from Earth.

Researchers observed stars as young as 10,000 years old, and others as old as 100,000. A 10,000-year-old star, called a Class 0, is equivalent to a one-day-old baby. A Class-1 protostar is as old as 100,000 years, and equivalent in age to a one-week-old baby. A mature star can be millions or billions of years old.

"These are the youngest stars so far detected in X-rays," Bally said. "But the X-ray activity is even stronger than we believed."

Scientists believe that stars form when gas clouds collapse due to gravity. As the gas becomes more dense, the cloud heats up and radiates energy. Then the cloud begins to rotate, and dust builds up into a flat disc, or protostar, in the center of the cloud.

Up until now, scientists had only been able to see the dense cloud around baby stars. They could guess that protostars were forming based on the behavior of the gas clouds but could never see through this "cocoon."

Scientists proposed looking at the Orion constellation because of the sheer number of baby stars there.

"We knew that it had at least 200 young stars," Bally said.

Chandra, the most sensitive X-ray telescope in use, has let scientists see the violent flares of hot plasma shoot away from the baby stars.

As the young ones mature, their violent behavior lessens and the cloud cocoon condenses into the star. Because the gas cloud is absent in adult stars, scientists do not have problems seeing them with strong telescopes.

"It takes millions or tens of millions of years to become an adult star," Bally said. "We are seeing the same types of processes ... in these stars that happened in our sun billions of years ago."

About 5 billion years ago, the Earth's sun was born from a gas cloud. Several million years later, hydrogen fusion began in the sun's core, and the star became the steady source of energy that allowed life to form on Earth.

"We had suspicions that there should be hot plasma on baby stars, but we now have strong confirmation that hot plasma does exist," Reipurth said. "This points to a very dynamic process in stars."