The very first stars
BY DR EMILY BALDWIN
ASTRONOMY NOW

Posted: August 5, 2008

Thanks to a revolutionary new computer simulation created by astrophysicists from Japan and America, the very first instance that stars breathed light on the Universe have been mimicked.

The Universe began with the big bang about 13.7 billion years ago, and within a few hundred million years the first stars were born, ending the cosmic dark ages and setting the stage for everything that followed. But since those first stars are now long dead and gone no one knew how they came into existence, until, that is, Dr Naoki Yoshida from Nagoya University in Japan, and colleagues, put together a computer simulation based on the very simple physics that governed the first moments of the Universe. They found that tiny density fluctuations in matter, gases, and even dark matter grew under the influence of gravity to seed the formation of the very first protostars.

“When first stars form is critically dependent on how rapidly structure grows by the action of gravity, and how rapidly structure grows depends on the matter density of the Universe, such that structure forms slowly in a Universe with a very low matter density because there is not enough sources of gravity,” explains Yoshida. “The simulations show one example of many protostars that would have formed early. One of our findings is that there is always a single protostar forming first in a large gas cloud, that is, we didn't find a cluster of protostars forming from a gas cloud.”

The simulation shows the predicted gas distribution around the first protostar formed from a self-gravitating, star-forming cloud and evolving into a core that can synthesize elements. The colour scale from light purple to red represents the increasing density of hydrogen. Image: Yoshida et al, Science, 1 Aug 2008.

The first stars were a lot different to our life-giving Sun. The simulations show a protostar with a mass just one percent of the Sun that eventually evolves into a more massive star up to one hundred times the mass of the Sun and capable of synthesizing heavy elements soon after the big bang.

"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 in the origins of life and planets," says Lars Hernquist from the Havard-Smithsonian Centre for Astrophysics, and one of Yoshida’s co-authors on a paper published in Science this week.

"The abundance of elements in the Universe has increased as stars have accumulated," he continues, "and the formation and destruction of stars continues to spread these elements further across the Universe. So when you think about it, all of the elements in our bodies originally formed from nuclear reactions in the centres of stars, long ago."

Performing a survey of stars in the Milky Way that contain just a small amount of these heavy elements could reveal the imprint of the first stars that produced those elements, allowing the astronomers to test their theoretical predictions prior to the launch of the James Webb Space Telescope in 2013 which will study the first galaxies, the next piece in the jigsaw puzzle of the Universe’s evolution.

Ultimately the astrophysicists hope to understanding how the protostars grow, layer by layer, to eventually form a massive star that can initiate nuclear reactions in its core, as well as being able to predict the mass and chemical properties of the first stars. But once the first protostars were created, the physics of the Universe became a lot more complicated and even more powerful computational resources will be required to achieve this ambitious goal.

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