Seeing the first stars

The first stars were born out of the darkness that reigned in the universe after the background radiation cooled below naked-eye visibility. They started as small density fluctuations in the dark matter that dominated the universe. By the time the universe was some 100 million years old, the dark matter in the higher density regions had started to collapse under the influence of gravity. Ordinary hydrogen and helium gas, a small percentage of the mass accounted for by dark matter, started to fall toward these concentrations.

The movie shown here picks up the story of one of these collapsing clouds when the universe was 155 million years old. The simulation, performed by astronomers Tom Abel of Pennsylvania State University, Greg Bryan of Oxford University, and Mike Norman of the University of Illinois, zooms in on a collapsing protostar that begins with about a million solar masses of material. At the end, a first-generation star with about 200 times the mass of the Sun is born.

These initial stars played a huge role in the evolution of the universe. They created the first significant amounts of elements heavier than helium and, when they blew up as supernovae, spread those heavy elements throughout the developing universe. This material was then incorporated into a second generation of smaller stars, which were much more similar to the Sun. Astronomers are searching the sky for examples of these second-generation stars.