Scientists have known for some time that most of the stuff in the Universe is so-called dark matter, material that cannot be seen directly because it does not interact with light.  That makes it very difficult to study.  But now, as we hear from VOA's Jessica Berman, researchers say the arrangement of the oldest stars in the universe may provide clues to help them learn more about dark matter.

Immediately after the Big Bang, experts say the universe expanded rapidly, but stayed mostly smooth and dark for about 100 million years.

Then things began to change. Scientists say that within that blanket of darkness, dark matter began to exert forces that pulled hydrogen, helium and lithium gases together to form stars.  

"You may say, why care about the first stars in the Universe?  But the first stars produced the first light in the Universe," he said.

That is Astronomer Tom Theuns at Britain's Durham University. Writing in the American journal Science.  Theuns and his colleagues describe a way that those stars, which are billions of years old, may help today's scientists unravel part of the dark matter mystery.

It depends on whether those oldest stars are in long strings or clumped together.

The dark matter that existed soon after the Big Bang may have been either "warm" or "cold."  Those are the terms astronomers use to describe how much energy the matter contained, or more simply, how fast its particles moved. The researchers developed a sophisticated mathematical model to show that stars would have clustered together in clumps under the influence of cold dark matter. In contrast, warmer dark matter would have produced stars in long strings, or filaments. Theuns says his theory may provide at least part of an explanation for the origin of the super-massive black holes at the center of some galaxies.

"So what we think is possible that is that in these filaments that you form in warm dark matter, if you form many stars along this filament, that you will get collisions between the stars," he added.  "So, soon collisions between the stars will make up a star that are so massive that it cannot remain a star, it becomes a black hole. And once it becomes a black hole, it can grow very rapidly by swallowing these stars that are around."

Astronomers do not yet have telescopes that can see the distant stars that were formed some 13 billion years ago, when the universe was young, so even if Theuns' theory is correct, it still does not provide any immediate insight to the nature of dark matter, even though it suggests that dark matter may have had a crucial role in the arrangement of stars in the early universe.