Astronomers snagged their first large cluster of quasars in 1982, says Roger Clowes, an astronomer at the University of Central Lancashire in Britain and the leader of the research team reporting the new results. By 1991, two more large clusters had been found. With the advent of the Sloan Digital Sky Survey in 2000, more have appeared, including the latest discovery.
But the latest find, which the team has informally named the Huge Large Quasar Group, or Huge-LQG, is the biggest so far. It lies some 8 billion to 9 billion light-years away and contains 73 quasars. These quasars represent the tip of the iceberg, with many more galaxies present in the group that are too faint for researchers to see. The team estimates the Huge-LQG's mass at more than 3,000 trillion times the mass of the sun – or about 1,300 times the mass of the Coma Cluster, which hosts more than 1,000 galaxies.
Collectively, these large quasar groups represent about 10 percent of quasars cataloged so far, "so they're not that common," Dr. Clowes says. "But when they occur, they can be quite dramatic."
Interest in this latest large quasar group stems from assumptions – the cosmological principle – that Albert Einstein made as he applied his equations of general relativity to the cosmos. The assumption greatly simplified his calculations, which pointed to a size threshold for individual structures beyond which the distribution of matter would appear uniform.