Hoary tales

Analysis of about 90 quasars in the ongoing quasar survey at the 500 cm telescope at Mount Palomar, California, has shed some interesting light on the ages of quasars (see accompanying story). From the redshift data, it seems that most of the quasars formed and faded away in a short time period (by cosmological scales). This is the conclusion of M Schmidt, D Schneider and J Gunn who conducted the study (Science, Vol 269).

They believe that there may have been an era of quasars some 2 billion years after the big hang when these objects were formed and flourished.