Sounding out the universe: How big, how old?
Astronomers peering deeply into space - hence, far back in time - have recently reported significant new facets of the early universe. But they still can't decide how old and how big the cosmos actually is.
An astronomical team at the University of California (Berkeley) has published a list of the most distant galaxies yet known. One of them is calculated to be 12 billion light-years from Earth. The astronomers say they may be seeing this galaxy as it was when the universe was only one-third as old as it is today. This presumes the universe was born in a vast primordial explosion of energy - the Big Bang - some 18 billion to 20 billion years ago. Some astronomers would dispute such a hoary age.
Meanwhile, British observers have found new members of the family of objects known as quasars (quasi-stellar radio sources) out near the edge of the observable universe, where few such objects were expected to be. Astronomers now may have to revise their notion of the makeup of the very distant, very early universe.
In reporting their quest for our cosmic history, the astronomers' use of words is important. Words referring to time and distance are virtually synonymous. The radiation by which we observe an object a billion light-years away left that object a billion years ago. We see it now as it was then. Likewise, qualifiers such as ''may'' or ''observable'' reflect the underlying uncertainties of this research enterprise. Astronomers can deal only with what can, at least in theory, be observed from Earth.
They speak tentatively of the implications of their findings because they aren't even sure they know what they are talking about when they speak of the distance of an object or the age of the universe. Theoretical assumptions are built into the determination of such things. Thus, when a research team says a galaxy is 12 billion light-years distant, with an age one-third of that of the present universe, its members are in open disagreement with astronomers who believe the ''observable'' universe to be only 10 billion years old.
It is from this perspective that the newly reported findings should be viewed.
The galaxy distances were determined by Hyron Spinrad and Stanislav Djorgovski in California. The galaxies themselves have been known for some time as sources of radio noise. Spinrad and Djorgovski identified these sources with optically visible galaxies. They then measured the light spectra from the galaxies and, from these, derived their distances.
Distant objects are retreating from Earth as part of the general expansion of the universe. The farther they are, the faster they recede. Their speed is reflected in the light they emit. Light of different wavelengths appears longer (redder) than it would if the source were not moving. Also, the faster an object moves away, the redder its light appears. Thus faster speeds, which imply larger distances, are associated with greater red shifts.
This is where the assumptions come in. The relationships between speed, distance, and red shift depend upon an astronomer's assumptions as to how the universe is structured and how it is evolving. This is why some astronomers, such as Allan Sandage and Gustav A. Tammann of the Mount Wilson Observatory, insist that the universe is 20 billion years old, while others, such as Gerand de Vaucouleurs of the University of Texas, come up with an age of only 10 billion years.
What Spinrad and Djorgovski have measured is the red shift of a galaxy's light. They now have nine galaxies with red shifts greater than 1. The most distant of them has a red shift of 1.819 - meaning the wavelength of the light measured is 1.819 times as long as it would be if the galaxy were not moving relative to Earth. This is the longest galactic red shift yet detected. Astronomers are now seeing galaxies farther away than any seen before. This extends research on cosmic evolution ''into previously uncharted territory,'' the two astronomers say. But the distance of 12 billion light-years estimated for that most distant galaxy should not be taken too literally.
The British discovery of new quasars also extends research on cosmic evolution into uncharted territory. And it, too, is subject to similar reservations.
Quasars are objects so powerful they can outshine an entire normal galaxy, yet they are thousands of times smaller. What they are and what powers them is still not understood. They also have the largest red shifts known in the universe. The record-holder and, presumably, the most distant has a red shift of 3.78.
Few quasars have been found with very large red shifts. Out of thousands of known quasars, only a few dozen have red shifts greater than 3. This has led some astronomers to suggest that such objects peter out beyond a distance of about 10,000 light-years. If true, this would mean that quasars were not characteristic of the early universe.
Now, however, Cyril Hazard of Cambridge University's Institute of Astronomy suggests that the lack of distant quasars is really a lack of good observing technique. The standard photographic emulsion used to record data is insensitive to long-wavelength light, so it may not register the heavily red shifted light from very distant quasars - that is, light with a red shift greater than 3.5.
Switching to a more suitable emulsion with a British telescope in Australia, Hazard and his colleagues Roberto Terlevitch and Richard McMahon came up with a possible distant quasar where none had been seen before. Its existence was confirmed by Alec Boksenberg, director of the Royal Greenwich Observatory, using a more powerful instrument - Britain's Isaac Newton telescope in the Canary Islands. The quasar has a red shift of 3.68, making it the second-most-distant object known.
If Hazard and his colleagues are right, the distant universe - meaning the very early universe - may have plenty of quasars after all.
But whether they are nearer 10 billion years or 20 billion years old is an open question. As astronomer Paul Hodge of the University of Washington has observed, ''Considering the immensity of the job, we should feel fortunate that we are now able to argue about only a factor-of-2 difference.''