Quartet of quasars discovered for the first time

Image of the region of the space occupied by the rare quasar quartet. The four quasars are indicated by arrows. The quasars are embedded in a giant nebula of cool dense gas visible in the image as a blue haze. The nebula has an extent of one million lightyears across, and these objects are so distant that their light has taken nearly 10 billion years to reach telescopes on Earth. This false color image is based on observations with the Keck 10m telescope on the summit of Maunakea in Hawaii.

Hennawi & Arrigoni-Battaia, MPIA

A quartet of quasars has for the first time been found in close proximity, a discovery that could challenge ideas about how galaxies and galaxy clusters formed.

Believed to the nuclei of early galaxy formation, quasars are powered by the increase of matter onto a supermassive black hole at the center of a galaxy.

Quasars are exceedingly rare and are usually separated by hundreds of millions of light-years. The researchers estimate that the odds of discovering a quadruple quasar by chance are one in ten million.

"If you discover something which, according to current scientific wisdom, should be extremely improbable, you can come to one of two conclusions: either you just got very lucky, or you need to modify your theory," said Joseph Hennawi of the Max Planck Institute for Astronomy in Heidelberg, Germany. Hennawi was one of the authors of a study on the findings, published today in Science.

These quasars are believed to have formed when the universe was half its current age. Images show the region as it was 10 billion years ago, or less than 4 billion years after the Big Bang.

The presence of multiple quasars may suggest the formation of what are called protoclusters, the forerunners of massive galaxy clusters. The protoclusters - coupled with the fact these quasars are surrounded by a giant nebula of cool, dense gas - could force scientists to reconsider the models of quasar evolution and the formation of the most massive cosmic structures.

"Our current models of cosmic structure formation based on supercomputer simulations predict that massive objects in the early universe should be filled with rarefied gas that is about ten million degrees, whereas this giant nebula requires gas thousands of times denser and colder," Sebastiano Cantalupo, one of the study's co-authors from UC Santa Cruz and ETH Zurich.

But if they are so rare, how did the researchers find them?

It helped that the cool, dense hydrogen gas, which emits light because it is irradiated by the intense glare of the quasars, surrounds the four quasars. In addition, both the quartet and the surrounding nebula reside in an unusual region of the universe with a surprisingly large amount of matter.

"There are several hundred times more galaxies in this region than you would expect to see at these distances," said J. Xavier Prochaska, the principal investigator of the Keck observations, where researchers used the 10-meter Keck I Telescope at the W. M. Keck Observatory in Hawaii to find the quasars.

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