When Galaxies interact, it’s Not all Fun and Games

qqqcol3icon2.jpgToday’s round of press conference started with the story of three systems that have mutually triggered fireworks in one another’s cores. Specifically, a gravitationally bound system of three quasars has been located at a distance of roughly 10.4 billion light years (z = 2.076). This is the first such triple quasar system that has been located.

So, why should any one care? Well, quasars are giant black holes in the process of feeding on gas and dust (and maybe even stars and planets) that just happen to get too close). By giant black holes, I mean black holes that are hundreds of thousands to tens of billions of times larger than the Sun. And, by feeding, I mean they are chowing on solar system masses worth of gas and dust with each bite, and sometimes spraying jets off high-energy particles while giving off light in ways that make these things the brightest shining actors in the entire universe. One quasar is just cool, and getting three cool things together all at once is, well, something that naturally attracts the observational astronomy paparazzi (or atleast grad students seeking projets).

More scientifically, we have a lot of theories on how galaxies form and grow from the start of time to today. These theories indicate that galaxy mergers and quasar activity were both more prevalent in the past, with the epoch of quasars peaking around a redshift of z = 2, when the universe was just 2 billion years old. While we’re still working to understand the physics of quasars, it seems that quasar activity is related to galaxy-galaxy interactions, and galaxy interactions should occur in large numbers at similar times. Thus, theoretically, if you are going to find interacting systems of QSOs, it makes sense that you find them somewhere near z = 2. This triple system was found at z = 2.076, matching that theory.

This system, QQQ 1432-0106, was initially identified as a potential double quasar gravitational lens. This means, it was identified as a system where a single distant quasar had its light bent by an intervening massive object such that it appeared as two objects rather than one. This is a common effect, with quasars being found split into as many as 5 different apparent objects (You can read more aboutthis effect here. Additional observations of these two objects, however, turned up a third object, and gravitational lensing models cannot replicate these observed pattern of three objects and their luminosities. The luminosity ratios of the quasars are 1: 25 : 200. This, in non-straight forward ways, reflects differences in mass, with the brightest system being approximately billions of solar masses and the second brightest being hundreds of millions of solar masses.

Spectroscopic observations of these systems give additional evidence that these are three physically related objects instead of a gravitational lensed single object. While all three systems have similar emission lines and appear at the exact same redshift, there are minor differences in the spectra that indicate slightly different distributions of material are present in the three systems.

Our current understanding describes this as a system consisting of three physically related interacting quasars that will eventually merge together. A possibly disturbed galaxy is visible around the brightest of these three quasars. The supermassive black holes in their cores – the angry monsters that power the quasar light – will interact in ways that may result in one or more of the supermassive black holes. This theory-based result has interesting implications. It is possible that there are free-roaming supermassive black holes wandering the universe, periodically consuming intra-galactic dust and gas. It also raises questions on how today’s galaxies end up with central supermassive black holes that have sizes directly related to the characteristics of the parent galaxies. This time, theory leaves us in a place without a lot of observational evidence to support us. To verify our concepts, astronomers need to identify galaxies lacking supermassive black holes, galaxies with supermassive black holes of unusual size (too small, rather than too large like ROUS*), or catch a system in the process of ejecting central black holes during merger. (for neat animations, see This Site.)

So, at the end of the day, some theories have added evidence, and some theories leave us asking questions, but no matter what, the quasars are spectactular and the science in this bit of observing is solid. This is a case of good science, done right, going through the scientific process to correct false starts and firmly establish this as the first gravitational interacting three quasar system. Kudos to George Djorgovski (CalTech) and his team for a job well done.


*Rodents of Unusual Size, from the Princess Bride

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