Quasar illuminates the most distant past.

Quasar illuminates the most distant past

A team of astronomers has identified the most distant object now known in the universe -- a quasar that was already emitting vast quantities of light only a billion years after the Big Bang. The discovery that such an object existed so early in the universe's history imposes severe constraints on theoretical models of how the universe evolved and how galaxies formed.

The astronomers determined the object's distance by measuring its light spectrum. As seen by Earth-based observers, light from distant objects is shifted to the red end of the spectrum. The more distant the light source, the greater this change in wavelength appears.

The record-breaking quasar, one of five high-redshift quasars recently found by Donald P. Schneider of the Institute for Advanced Study in Princeton, N.J., James E. Gunn of Princeton University and Maarten Schmidt of the California Institute of Technology in Pasadena, has a redshift of 4.73. It is so far away that its light takes more than 10 billion years to reach the Earth. The astronomers report their discovery in the December ASTRONOMICAL JOURNAL.

The discovery of a quasar with such a high redshift suggests that galaxies with massive black holes at their cores already existed when the universe was less than 7 percent of its present age. Moreover, the fact that astronomers have so far detected no obvious differences between light spectra from nearby and more distant quasars implies that galaxies in the distant past contained roughly the same materials as later galaxies.

"Considering how far away and therefore how far back in time these things are, it tells you that the elements were already in place in abundances similar to those we seem to see in our own neighborhood," says Patrick S. Osmer of the National Optical Astronomy Observatories in Tucson, Ariz.

These findings increase the difficulty of reconciling the extraordinary smoothness of the cosmic background radiation -- heat left over from the creation of the universe -- with the lumpiness of matter as it now appears in the form of galaxies (see adjacent story). By shortening the time in which the transition from smoothness to lumpiness must take place, the new observations effectively rule out a variety of theoretical models for the development of structure in the universe. For many cosmologists and astrophysicists, it's back to the thinking phase.