Primordial "Heavy Hydrogen" Promotes Big Bang Theory May 16, 2001 Astronomers using the giant 10 meter Keck telescope have made the most precise measurement to date of the amount of deuterium, or heavy hydrogen, in the universe. This finding provides a stringent constraint on the Big Bang theory for the origin of the universe. Led by David Tytler of the University of California, San Diego, a team of six astronomers observed absorption lines in light from a quasar. Specific wavelengths of the quasar light were absorbed by various types of atoms in an intervening, and very distant intergalactic cloud. They determined that the cloud contained about one deuterium atom for every 40,000 normal hydrogen atoms. This number, which is consistent with other independent measurements, gives the team confidence that they and other scientists are closing in on one of the most important pieces of evidence for proving the Big Bang theory. "According to the theory, primordial deuterium was created by nuclear reactions in the first one thousand seconds of the Big Bang," explained Tytler. "The amount depends sensitively on the number of protons and neutrons present, so if we measure the deuterium, we can determine how many protons, and therefore how much matter is present in the universe." The method used by the team is considered to be the most accurate approach to measuring the elusive deuterium isotope of hydrogen because they are looking back in time to observe clouds in the early universe. Deuterium is destroyed by the formation and evolution of stars, so it is advantageous to search for deuterium in gas clouds while they are in a relatively pristine state. This is the fourth measurement of this type undertaken by the team. According to John O'Meara, the lead author on the paper describing the research which appeared in the May 10 issue of The Astrophysical Journal, this result is the most accurate. "The other clouds were complex systems which made the observations more difficult to interpret," he said. "The fact that we found fair agreement with the other clouds makes the determination of primordial deuterium much more robust." The result implies that in the first fraction of a second of the Big Bang, the universe was composed almost equally of matter and anti-matter. For every 2 billion anti-protons, there were 2 billion plus one protons. When combined with data from other types of telescopes and investigations, the following picture emerges. The universe is composed of four percent protons, electrons and other familiar particles, about thirty percent is in some mysterious, invisible form of matter called dark matter, and about sixty-six percent is in a still more mysterious form of matter-energy called dark energy. The team involved in this research also included David Kirkman, Nao Suzuki, Dan Lubin and Arthur Wolfe of UCSD's Center for Astrophysics and Space Sciences, and Jason Prochaska of the Observatories of the Carnegie Institute of Washington. Some of the observations were also made with the Shane 3 meter telescope at the Lick Observatory. This research was supported by the National Science Foundation. Science Contacts: David Tytler (858) 534-7670 dtytler@ucsd.edu John O'Meara (858) 822-2018 jomeara@ucsd.edu CASS/UCSD