WSJ wrote:SCIENCE JOURNAL
By ROBERT LEE HOTZ
The Making of the First Star
Computer Experiment Captures
The Universe in Its Infancy
Following the Big Bang
August 22, 2008; Page A9
In the beginning, there was a computer simulation.
Running on 70 linked computer processors, it encoded in its circuits the universe as it existed more than 13 billion years ago, shortly after the Big Bang, when gravity stirred billows of primordial hydrogen and helium. Programmed to respond only to the natural laws of physics and chemistry, the virtual gases compressed to form the seed of the first star. Then, it ignited -- a star unlike any known today flickering like a candle in the dark basement of time.
Through this computer experiment, made public in the journal Science this month, Japanese and U.S. cosmologists for the first time reliably replicated the recipe for the first star. The protostar they produced was the pilot light for a primordial orb that grew rapidly to 100 times the mass of our own sun. Through succeeding generations of stars, these stellar furnaces forged hydrogen, helium and lithium into all of the other elements of the periodic table, including the star stuff of which we all are formed.
This experiment in theoretical astrophysics fills a crucial gap in the scientific narrative of creation. Insights into the origins of early stars may serve as a cosmic Rosetta stone to help scientists decipher the lingering mysteries of star formation.
"Ultimately, this story of the first star is the beginning story of our own existence," says astrophysicist Naoki Yoshida at Nagoya University in Japan, who led the research team. "Our body contains carbon, oxygen and so on. These elements did not exist in the early universe. We are here because these elements were synthesized in stars."
All told, the scientists spent almost eight years perfecting their computer experiment. Each run of the simulation took a month of computer time. Although their universe exists only as a set of equations operating in a supercomputer, it is more than theory. It is based, in part, on direct observations of the infant universe as revealed today through faint patterns of microwave energy collected by sensors such as NASA's Wilkinson Microwave Anisotropy Probe satellite.
During its seven years orbiting 1.5 million kilometers above Earth, the WMAP has been measuring cosmic microwave background radiation, which still carries an imprint of conditions 380,000 years after the Big Bang 13.7 billion years ago. Then, the expanding universe was perhaps 1/1,100th its current size -- and the physics that governed it was simpler. "This mind-boggling endeavor is made possible by the extraordinary simplicity of the early universe," says astrophysicist Volker Bromm at the University of Texas, Austin.
WMAP data released in March show what little resemblance that infant universe bears to the cosmos we now inhabit. In the early cosmos, elementary particles called neutrinos made up 10% of the universe, atoms 12%, dark matter 63%, photons 15% and the enigmatic force called dark energy was negligible, according to data from the $150 million probe. Today, when only about 5% of the universe is composed of matter we can actually detect directly, neutrinos have dwindled to less than 1%, atoms to about 4.6% and dark matter to 23%, while dark energy now accounts for 72%.
By the time the microwave light collected by WMAP was first emitted, the cosmos had cooled enough that protons and electrons could form hydrogen, helium and traces of lithium, the scientists said. There still were no stars, no galaxies, no physical structure of any sort, only minute variations in the density of the hot gases caused by temperature differences and, perhaps, by invisible filaments of mysterious dark matter.
"What we see in these very faint fluctuations are the seeds of structure in the universe," says Gary Hinshaw at NASA's Goddard Space Flight Center in Maryland, where he leads the data analysis for the WMAP science team. "That is what Yoshida's group used for their initial conditions, to study the formation of the first objects in the universe -- how we went from almost featureless gas to gas that has structure and, ultimately, to massive stars and galaxies."
The star seed that took form in Dr. Yoshida's supercomputer had barely 1% of the mass of our own sun and a density about 1/100th of water. By their calculations, that protostar should grow to more than 100 times the sun's mass in 10,000 years. "Compared to the age of the universe, that is the blink of an eye," says study co-author Lars Hernquist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.
Massive enough to synthesize heavy elements, this primordial star was also more luminous than our sun, emitting more ultraviolet radiation, the scientists said. It burned out more quickly -- in a million years or less, compared with an estimated lifetime of five billion years or so for our sun.
In our universe now, new stars are born every day. But the conditions of that birth are so complex that scientists have yet to completely understand them all. Last month, NASA's Jet Propulsion Laboratory announced the discovery of a remote galaxy 12.3 billion light years away in which stars are born at a rate of 4,000 a year, compared with an average birth rate of 10 new stars annually in our own Milky Way. The most luminous of these contemporary stars -- called Eta Carina -- blazes with the light of an estimated 4.7 million suns.
"These stars -- the first stars -- were rather different from the stars like the sun we see today," says Dr. Hernquist. "But they affected everything that happened after them."
• Robert Lee Hotz shares recommended reading on this topic and responds to reader comments at WSJ.com/OnlineToday. Email him at sciencejournal@wsj.com.
Pretty cool.
