New Telescope Seeks `Big Bang' Evidence
GIVE a scientist a more powerful version of an old instrument, and she may open a new era for an old line of research. Critical knowledge that was beyond the grasp of the older equipment suddenly is available to bring new insight into the fundamental nature of the universe.
That's what University of Hawaii astronomer Antoinette Songaila and colleagues have done.
Using the new 10-meter (394-inch) Keck telescope on Hawaii's Mt. Mauna Kea, they have begun what promises to be a definitive check on the favored theory of the birth of the universe, on the synthesis of the first elements, and on the amount of ordinary matter in the cosmos.
Astronomers have been trying to get this kind of information for decades, but their telescopes have been too small. Not even the Hubble Space Telescope could help them. Its forte is a sharp eye for detail unobstructed by Earth's atmosphere.
Atmospheric absorption and distortions don't affect the kind of observations involved in these studies. What's needed is raw light-gathering power that can build up enough data so that the ``signal'' - the meaningful information - the astronomers want pops out clearly above the data's random ``noise''.
Dr. Songaila, her Honolulu colleague Lennox Cowie, and Craig Hogan and Martin Rogers of the University of Washington in Seattle are after a very weak signal indeed. They are looking at how light from a distant object is absorbed by a cloud of primordial gas that also is very far from Earth.
The two Keck 10-meter telescopes - the first of which is operational - can sketch the spectrum of that absorption. This shows which wavelengths of light are absorbed and how strongly they are absorbed, and reveals the cloud's composition.
Astronomers want to know the abundance of deuterium, the double heavy form of hydrogen. According to standard ``big bang'' theory, our present universe emerged from a primal explosion of energy. This formed the protons and related particles that make up ordinary matter. The theory specifies how much of the lightest elements - principally hydrogen - was formed. Most other elements have been built up from hydrogen in the nuclear furnaces of stars.
This theory is tied together in such a way that the amount of ordinary matter the universe now has is directly related to the amount of deuterium produced in the ``big bang.'' Furthermore, that's all the deuterium the universe can ever have.
Some of it has disappeared over time as stars process it, along with the much more abundant ordinary hydrogen, to produce helium. Thus, deuterium abundances measured in or near our own galaxy do not represent deuterium's primordial abundance.
Astronomers would like to measure deuterium abundance as it was originally. That means measuring it in a gas cloud very far from Earth so that the light by which the measurement is made began its journey when the universe was young.
As they reported in Nature, Songaila and her associates studied a distant gas cloud that absorbs light from an even more distant quasar - a highly energetic object that is much smaller than an ordinary galaxy. They find an abundance of about two deuterium atoms for every 10,000 atoms of ordinary hydrogen. That squares neatly with ``big bang'' theory, but implies that the universe has less ordinary matter than astronomers had previously thought.
If confirmed, this also implies that the universe has more mass in a form not yet identified than astronomers had suspected. The Keck data also give a measure of the temperature of radiation left over from the ``big bang.'' This measurement too is in line with the standard theory.
These are early results. They still have uncertainties. But the Keck instrument will make many more such observations that should clear these matters up. That prospect should delight all astronomers.