Until new tools can peer more deeply into that gap, simulations remain the only vehicles for exploring the transition.
In a young, dark universe
The research team, led by Nagoya University's Naoki Yoshida, started with a universe dominated by recently discovered dark energy and by cold dark matter, which astronomers currently detect by its gravitational influence on matter they can see. Hydrogen dominates the small percentage of "normal" matter in this young, denser universe. It's in a form that renders it opaque to light.
The simulation picks up the story when the universe was roughly 300 million years old and 20 times more compact that it is today. The afterglow of the big bang had long since faded. Subtle variations in the density of dark matter across space led to regions where dark matter was more dense than others.
The simulation focuses on one of these denser areas, or halos. There, dark matter's enhanced gravity corrals hydrogen. The hydrogen cloud undergoes alternate periods of heating and cooling as it contracts due to gravitational collapse. It also shifts from cloud to flattened disk and finally to a stable, spherelike proto-star.
At this stage, with 1 percent of the sun's mass (or about 10 times Jupiter's mass), the proto-star's internal temperature has risen high enough to generate an outward pressure that prevents further collapse.