first_star_011115 Astronomers have created a computer simulation showing how the first star in the universe might have formed, helping to plug a gap in understanding of the timeline of the early cosmos.
The simulation shows how exotic and invisible "dark matter" formed clumps that attracted normal matter, which collapsed and formed a giant star. The result implies that the first light in the universe was created by a single fiery furnace, not by some instantaneous creation of a galaxy or cluster of stars.
The study does not represent an actual observation, but scientists said it provides significant insight into what might have happened in the first few million years after the Big Bang, when a smooth and dark universe became lumpy and illuminated.
| See the animation |
| This animation zooms in on the first star in the universe, showing closer and closer views of the new star as envisioned in the new computer simulation by Tom Abel and colleagues. |
The research team, led by Tom Abel at the Harvard Smithsonian Center for Astrophysics, says a lone object developed out of a cloud of raw material, a first star that became one of many seeds that later formed the
first galaxies.The first star, along with others that presumably formed soon after in a similar manner, died quickly and cannot be seen or studied today. So astronomers have long wondered how such objects formed.
"Significant progress is being made in this area and we are very close to finding a solution to how the first stars formed," said Morris Aizenman, senior science associate in the Mathematical and Physical Science Directorate of the National Science Foundation.
"Abel's study is a significant step forward," said Aizenman, who was not involved in the work but has examined the methods and results.
A paper describing the simulation was published Thursday in Science Express, an online sister publication to the journal Science. Greg Bryan at the Massachusetts Institute of Technology and Michael Norman of the University of California-San Diego developed the sophisticated computer code used by the team and also worked on the research.
A simple palette
Most stars today are rich in metals. But the early universe was metal-free.
Astronomers have long assumed that the first stars must have been an as-yet-unknown metal-free variety, and that they exploded soon after they were born, forging metal and flinging it into space. Later, the more diverse array of material would have been gathered up to make second- and third-generation stars.
Since it is not yet possible to see these earliest stars, researchers employ computers to model what might have happened.
The task is complex, but the range of possibilities is simpler than one might think, because there was little to work with in the infant universe. Most of the material and processes that makes modeling today's universe incredibly complex simply didn't exist back then.
There were no magnetic fields. No space dust. No cosmic rays. And only a handful of chemical elements existed.
After the Big Bang, estimated to be between 12 and 15 billion years ago, the universe was composed mostly of
dark matter, invisible particles that are widely accepted to exist but have not yet been detected. A relatively smooth distribution of dark matter and some normal matter, mostly hydrogen atoms, permeated the young cosmos, theorists say.But lumps and bumps developed, catalysts that were destined to form something.
The first star
Abel explained for SPACE.com how the new simulation shows the first star developing, and what his group's findings mean for theorists.
The process began just 13 million years after the Big Bang. Small perturbations had formed in the fabric of the universe. After 100 million years, dark matter is attracted to these "density fluctuations," as researchers call them. Over time, several draw together to form one larger clump.
Atoms of hydrogen are pulled in, too. The hydrogen is compressed and heats up, much like the air in a tire warms as you pump more air into it. Some hydrogen atoms, now pressed more tightly together, combine to form molecules -- molecular hydrogen.
The result is the development of a molecular cloud, something seen in our own galaxy today and known to be a
precursor to star formation.After 155 million years -- an eyeblink in cosmological terms -- a cloud of normal and dark matter has built up the mass of a million suns. In the center, a star about the mass of our Sun is born. The very first star in the universe.
Overindulgence
Nearby, however, at the center of the cloud and surrounding the new star, there is enough gas to make 200 more suns. The first star uses its newfound gravity to reel this gas in. The final mass of the first star is not determined by Abel's simulation, but it is thought to grow to gargantuan proportions.
There is a limit, however.
Scientists are convinced that a star more than 100 times as massive as the Sun is forced to explode in what's known as a supernova.
Given the material available to the first stars in the new model, they would likely have grown quickly and become so massive as to explode after just a few million years.
Abel said one of the most significant aspects of the simulation is that the collapse of material in the cloud happens so rapidly that it forms just one star, instead of being fragmented into several. And the first star would have cannibalized any effort to generate another nearby star.
"The star is so luminous in ultraviolet photons that it destroys all the hydrogen molecules that would be needed to form other stars nearby," he explained.
Over the past three decades, other theorists have suggested that the first objects to form in the universe might have been black holes or possibly clusters of stars. The new view, if it stands up, implies that "most of the speculations of the last decades, which assumed the cloud would fragment, are incorrect," Abel said.
Long gone
There is no chance of seeing one of these first stars in our galaxy.
"Since all these stars formed billions of years ago, they have already exploded by now," Abel said. "However, one is hoping to see signatures of these first objects in the images of distant galaxies. They are billions of light years away and hence the most distant of these galaxies perhaps still host some of the first stars."
So far, researchers have not spotted the most distant galaxies thought to have existed, but many believe they are
on the threshold of doing so.The simulation was done on the SGI Origin2000 supercomputer at the National Center for Supercomputing Applications at the University of Illinois. Abel said it is the first such set of calculations to simultaneously follow the collapse of material from cosmological scales down to stellar scales.
"The most amazing thing for us is that we can realistically recreate the events that made the first objects in the universe," Abel said.
More About Deep Space & Cosmology:
Astronomy News by TopicThis Week in Science & Astronomy:
advertisement
