New galaxy cluster may be biggest in known universe

A huge "supercluster" of galaxies discovered in the constellation Leo could be the biggest structure in the known universe, astronomers said yesterday.

A huge "supercluster" of galaxies discovered in the constellation Leo could be the biggest structure in the known universe, astronomers said yesterday.

The grouping of tens of millions of stars is about 6.5 billion light years from Earth and is estimated to be 500 million light years across, making it the largest collection of galaxies so far recorded by astronomers.

"We haven't found anything bigger in the literature," said Gerard Williger, an astronomer at Nasa's Goddard Space Flight Center and the National Optical Astronomy Observatories in Arizona, speaking at the American Astronomical Society in San Diego, California.

"And nobody has brought anything bigger to our attention, but I don't want to go out on a limb and say this is absolutely the biggest, because then that surely means somebody is going to come up and say, 'but wait ...'."

The structure of the galaxies was found by analysing the radiation emitted by more distant quasars, "quasi-stellar" objects that are sources of intense energy.

Quasars are active galaxies that have very bright cores, probably powered by giant black holes that suck in matter. They are helping scientists to map galaxies and explain the distribution of matter in theuniverse.

"We see these galaxies as they existed billions of years ago. The amount of matter connected with quasars and galaxies at such distances and distant times in the past is probably not the same as we would measure in the local universe today," Dr Williger said.

"So it's very important to find out how much mass we are actually looking at."

Astronomers observe galaxies as parts of groups, clusters and superclusters of stars. Our own Milky Way is a tiny feature in a relatively small supercluster of galaxies.