First Star in Universe Grew Fast

Star Light, Star Bright, First Star...

Aug. 1, 2008 -- Star light, star bright. The first star grew fast, but began slight. The first cosmological object formed in the universe was a tiny protostar with a mass of about 1 percent of our sun, according to U.S. and Japanese researchers who spent years developing a complex computer simulation of what it was like after the Big Bang that formed the universe.

This protostar was surrounded by a giant mass of gas and it grew to 100 times the sun's mass over about 10,000 years, according to Naoki Yoshida of Nagoya University in Japan. That is very rapid growth on a cosmic scale.

"The first stars were very different from stars like the sun," explained Harvard astronomy professor Lars Hernquist, co-author of a paper describing the findings in Friday's issue of the journal Science.

While the sun is mostly hydrogen, it also contains oxygen and carbon, he said. The early stars were primarily hydrogen and helium, and were much more luminous and had a shorter life.

"These differences have important implications for what happened afterward," he said at a teleconference.

"This general picture of star formation, and the ability to compare how stellar objects form in different time periods and regions of the universe, will eventually allow investigation into the origins of life and planets," Hernquist said.

The study may prove to be a "Cosmic Rosetta stone" suggested Volker Bromm, an assistant astronomy professor at the University of Texas.

Bromm, who was not part of the research team, said in a commentary that the findings could help researchers finally unlock the problem of understanding star formation, much as the Rosetta stone led to the understanding of ancient Egyptian writing.

The typical lifetime of these early stars was a million years or so, while a star like the sun can continue for 5 billion years.

Because of their short lifespan, none of the first generation of stars is still around, Hernquist said. But "we do see stars in our galaxy that have very different properties than our sun, and it's possible these are second-generation stars."

In the simulation, gravity acted on tiny variations of the density of matter, gases and the so-called "dark matter" of the universe after the Big Bang, forming the early stage of a star. That protostar would evolve into a massive star capable of synthesizing heavy elements, not just in later generations of stars, but soon after the Big Bang, according to the analysis.

Hernquist said the "abundance of elements in the universe has increased as stars have accumulated, and the formation and destruction of stars continues to spread these elements further across the universe."

"Dr. Yoshida has taken the study of primordial star formation to a new level with this simulation, but it still gets us only to the halfway point toward our final goal. It is like laying the foundation of a skyscraper," Bromm said. "We must continue our studies in this area to understand how the initially tiny protostar grows, layer by layer, to eventually form a massive star."

The research was funded by the Ministry of Education, Culture, Science and Technology of Japan and the Mitsubishi Foundation.