Rare quasar triplet lets astrophysicists glimpse cosmic structure

Triplets may be rare in humans, but they’re even more unusual to find in quasars. But now, an international team of researchers has discovered a quasar triplet about 9 billion light years away – only the second such trio ever discovered.

The strange structure is no mere novelty: Quasar triplet QQQ J1519+0627, described in a paper released Tuesday by the Monthly Notices of the Royal Astronomical Society, will give astrophysicists a look into the growth and development of the universe’s structure.

“We are using them to go and find galaxy clusters that are in the act of forming, essentially,” said coauthor Michele Fumagalli, an astrophysicist at the Observatories of the Carnegie Institution in Pasadena.

Quasars are extremely bright objects powered by matter falling into supermassive black holes sitting at the heart of galaxies. When two or more are spotted in the same structure, it’s a possible sign that two galaxies are in the process of merging.

Quasar triplets are difficult to pick out; they’re so far away that it’s hard to distinguish each quasar against the background fuzz. But by analyzing and modeling data from multiple telescopes – including from the La Silla Observatory in Chile and the Calar Alto Observatory in Spain – the researchers were able to make out the trio’s shape.

Two of the quasars are closer to each other than the third -- which means they’re likely the pair that first formed the system. The quasars sit close enough that their galaxies’ halos of dark matter – the invisible mass that fills the universe, connecting galaxy clusters in a sort of cosmic web – were probably touching. The galaxies holding these quasars, he added, appear to be on their way to melding together and forming one giant galaxy.

Fumagalli said he and the other scientists plan to search for other triplet candidates.

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