The protocluster itself is somewhat unusual, containing up to 20 times more galaxies than other already-dense objects of the same type. The light took about 10 billion years to reach scientists today, so they are seeing the protocluster as it existed in the early universe (which is only about 13.7 billion years old).

The nebula that's home to the four quasars sits within a protocluster, a forerunner of a galaxy cluster like those that exist today. That, in turn, could be an important piece of the puzzle for understanding what makes a galaxy turn on as a quasar.'

'We thus either have to conclude that we got really lucky - 1 in 10 million - or that quasar activity is much more likely to occur in certain environments. 'The primary significance of the quadruple-quasar system is the extremely low probability of a discovery like this occurring by chance, according to our current understanding of the abundance of quasars,' Hennawi said. While it is possible that the researchers simply lucked out - indeed, they dubbed the cool dense cloud of gas the 'Jackpot Nebula' - Hennawi said it is more likely that the discovery reveals more about how quasars might form. The research is published online today (May 14) in the journal Science. This, however, is the first known quadruple-quasar system. Two triple quasar systems have been found since 2007. Nearly 500,000 quasars have been identified so far, but scientists know of only about a hundred binary quasars.

Inside the cloud of gas, the researchers identified not one but four tightly packed quasars, all lying surprisingly close together. Selecting one likely candidate, the team trained a Keck telescope in Hawaii on the object, and found one of the largest and brightest Lyman-α nebulae yet discovered. The bright light of a quasar can illuminate the gas around it, helping astronomers to better understand the properties of the gas.

Hennawi and his colleagues were studying 29 quasars in search of a nebula of cool hydrogen gas, known as Lyman-α (Lyman-alpha) nebulae, surrounding them.

Quarky and quasars game