Leftovers from the Big Bang

June 15, 1995

In one of the more important discoveries in recent years, astronomers at Johns Hopkins University have detected in intergalactic space huge clouds of helium gas believed to have been left over from the birth of the universe. The finding represents another major piece of evidence supporting the theory that all matter, space and time came into existence in an immense cosmic explosion some 12 to 15 billion years ago.

The discovery was made using a Hopkins-designed telescope sensitive to the ultraviolet portion of the electromagnetic spectrum. The instrument was launched in March aboard the space shuttle Endeavor high above Earth's atmosphere, which normally blocks ultraviolet rays. Scientists were able to detect the presence of molecular helium by measuring how light from a distant quasar was absorbed as it passed through two of the gas clouds on its journey toward Earth.

The clouds themselves appear to be tenuous but immense collections of hydrogen and helium gas thousands of light years across (one light year is the distance traversed in a year's time by light traveling at 186,000 miles a second, or about 6 trillion miles). Scientists speculate there may be billions of such clouds floating around in the space between the galaxies and that, taken together, they contain five to 10 times more matter than the material in all the visible stars and galaxies. That's enough helium to fill a lot of balloons.

According to the Big Bang theory accepted by most scientists today, hydrogen and helium, the lightest elements, were the first to form after the primordial event. The gas in the recently discovered clouds is thought to date from atomic nuclei that coalesced within the first three minutes of the instant of creation. As the hot, young universe expanded and cooled over the next 1 million years, the hydrogen and helium nuclei joined with free electrons swarming through space to form the first atoms. All the heavier elements were formed later in the cores of stars.

The Hopkins team included astrophysicist Arthur F. Davidsen and his colleagues, Gerard A. Kriss and Wei Zheng. Dr. Davidsen says their discoveries will increase scientists' understanding of the structure of the universe. "It imposes new constraints on our theories and shows what it was like when the universe was about one-third as old as it is now," he said. The discovery was also a breakthrough for space astronomy and perhaps the most important new finding to be made by a space shuttle mission. We extend our warmest congratulations to Dr. Davidsen and his team.

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