If you’re ever discussing the most dramatic things in the known universe, then quasars should feature quite highly in the conversation. Some of the most distant objects we can see with our most powerful telescopes, these faraway cosmic jewels can shine with the power of a trillion suns. Seeing three of them in the same place is really quite a spectacle!
In fact, it’s an extremely rare spectacle. Quasars are rare objects to begin with. Finding two together is unlikely, let along three!
All the same, that’s exactly what a group of astronomers, led by Emanuele Farina at the University of Insubria in Como Italy, have uncovered — nine billion light years away, known by the ID number of QQQ J1519+0627. A triple quasar system like this is actually so rare that this is only the second one ever to be discovered! Wow!
Quasars are actually the ultraluminous cores of massive galaxies, whose greedy supermassive black holes are gorging themselves on infalling gas and dust. As black holes accrete matter this way, they surround themselves with a huge disk of material.
The colossal gravitational forces at play around a black hole cause tidal heating in disks like this, crushing and squeezing the material in the disk till it reaches extremely high temperatures. Any hapless stars or planets that may venture too near are mercilessly torn asunder. Even the supermassive black hole in our own galaxy is surrounded by corpse-like supernova remnants; stars that strayed too close to the monster.
This superheated disk of crunched up starstuff shines brightly across the entire electromagnetic spectrum, from radio waves through to gamma rays. So intense are the forces which these supermassive black hole accretion disks endure, that they can convert matter into energy more efficiently than the reactions occurring inside stars.
Being 9 billion light-years away, we’re seeing these quasars as they were a long, long time ago. Long before the sun had formed. Probably long before the giant interstellar cloud in which the sun condensed from had formed. The universe was a much younger place back when the light we’re now seeing left those quasars. Younger and smaller, so encounters between multiple objects may have had a greater chance of occurring. Multiple quasars like these are believed to be bound together by gravity, created by galaxies colliding with each other.
In this case, two of the quasars are quite close together, suggesting that they may be interacting. The more distant one, while also gravitationally bound, is less likely to have been involved in the formation of the system.
The only other known triple quasar was discovered as recently as 2007, going by the name of QQQ J1432−0106. At a rather more distant 10.5 billion light years away, it’s been studied well enough to know that these quasars are around 100,000–150,000 light years away from each other. To us, that might sound like they’re rather far apart, but it’s fairly typical for interacting galaxies.
One curious finding with the newest triplet, however, is the lack of ultra-luminous infrared galaxies (ULIRGs) nearby. This is contrary to what might be expected, as quasars and ULIRGs are commonly found in the same neighborhoods. The team that discovered these quasars suggest that this may mean that they’re part of a larger structure which is still forming as we see it.
Michele Fumagalli from Carnegie, one of the astronomers involved in this work, explained in a press release that, “Honing our observational and modeling skills and finding this rare stellar phenomenon will help us understand how cosmic structures assemble in our universe and the basic processes by which massive galaxies form.” Farina also noted that, ”Further study will help us figure out exactly how these quasars came to be and how rare their formation is.”
Image: An image of the three quasars from Calar Alto observatory, combined from Omega 2000 H and z band shots, and SDSS r-band data. The three components (appearing in blue) of the triple quasar QQQ J1519+0627 are identified. Credit: Emanuele Paolo Farina/Calar Alto