For only the second time ever, astronomers have discovered a triple quasar system - possibly part of a much larger structure.
Quasars are extremely bright and powerful sources of energy that sit in the centre of a galaxy, surrounding a black hole. Where there's more than one quasar, the bodies are held together by gravity and are believed to be the product of galaxies colliding.
Triplet systems such as this one are believed to be very rare - and, in any case, are very hard to spot as it's extremely difficult to distinguish the quasars from one another.
"Honing our observational and modelling skills and finding this rare phenomenon will help us understand how cosmic structures assemble in our universe and the basic processes by which massive galaxies form," says Michele Fumagalli from the Carnegie Institution for Science.
The team managed to find QQQ J1519+0627 by combining observations from the New Technology Telescope of the European Southern Observatory at La Silla, Chile and from the Calar Alto Observatory in Spain with advanced modelling.
It's nine billion light years away, which means its light was emitted when the universe was only a third of its current age.
Two members of the triplet are closer to each other than the third. This, says the team, means that the system could have been formed by interaction between the two adjacent quasars, but probably wasn't triggered by interaction with the more-distant third quasar.
And there was no evidence of any ultra-luminous infrared galaxies, which is where quasars are usually found.
As a result, the team proposes that this triplet quasar system is part of some larger structure that is still undergoing formation.
"Further study will help us figure out exactly how these quasars came to be and how rare their formation is," says Emanuele Farina of Italy's University of Insubria.