This triggered several Astronomy Cast listeners to write and basically say “Huh?” We addressed this a little bit in today’s questions show (real show to follow tomorrow or Wednesday – we had problems with a corrupt audio file over the weekend and got behind). I wasn’t able to give as thoughtful a response in the show as I might have liked however, so I’m going to try and write something here.

So, first, I’d like to say there are two ways to look at this: 1) In reality, 2) in make-believe land.

Make-believe land is oh so much more fun. So, lets imagine that somehow we are able to grow a very large blackhole in isolation. Then, using imaginary technology (we are in fantasy land, afterall), we throw a star at the supermassive blackhole (SMBH) so that it’s goes on a straight, uninterrupted path toward the SMBH. So straight, so perfect, infact, that if we could watch we’d see it hit on a line connecting the star’s center of mass with the SMBH’s center of mass. Now, the SMBH will simply slurp up this perfectly thrown star. Burp. No more star and no accretion disk. Now, If you, using your super duper, impossible, imaginary technology could throw a star with dead on aim over and over every second across all the epochs of time, you could pretty much build a SMBH as big as you wanted.

Here is where I stress this pretty much can not happen.

Let’s look at the reason’s briefly. First of all, the only way to easily get a SMBH all by itself is to have three galaxies merge together and one of the SMBH’s in the merging system gets ejected via three body interactions. (Pretty much any three body interaction between objects of similar masses leads to one of the masses getting spit out. This works for stars and black holes). So now I have an isolated SMBH hurtling itself through the intergalactic medium, passing rapidly through the space between galaxies. Yes, I can get a SMBH all by itself, but now I kind of have it hurtling through space.

So let’s image it lands in a nice friendly crowd of stars. As it hurtles in  through the stellar populations, stars will fall in from all sides, spiraling in and forming a disk. At the same time, any dust and gas that may be around will also get sucked in. Eventually, a thick disk of material from this thick pocket of stuff will form a nice hot disk that give off so much light and wind that anything new trying to fall in will simply get blown away before it can get so close that it can’t escape.

And it’s not like there is a lot of stuff to eat in this imaginary star cluster we have flung our imaginary SMBH into.

The reality of the universe is in many ways far more interesting then our imaginary scenerio and galaxies self-regulate the size of supermassive black holes through complex feedback mechanisms. In the rather cool paper mentioned above, astronomers Priyamvada Natarajan and Ezequiel Treister describe how a combination of winds and star formation regulate the size to which SMBHs can grow. They estimate the upper limit is roughly 10^10 Solar masses (10,000,000,000 Solar Masses).

Here’s how it works:

First of all, most galaxies just don’t have enough stuff around them to ever grow that big, and as the universe expands and carries non-gravitationally bound systems farther and farther apart, the potential for truly giant SMBH’s dimishes.

Second, while it is possible to grow what they term Ultra-Massive Black Holes, SMBH’s approximately the size of the 10^10 Solar Mass upper limit, it is hard to grow them bigger. These objects when they do exist, are in the hearts of cD galaxies sitting in the centers of large galaxy clusters. In these systems, the gas the SMBH can consum eventually gets pushed away when the luminosity of the accreting material reaches a certain threshold. Once the gas is pushed away, it really has no reason to fall back to the center and get eaten later unless something disturbs its orbit, and if that does happen, it will get pushed away again as soon as the accrestion luminosity again gets above a certain level.

In addition to clearing out dust and gas that isn’t currently trying to flow in, but happens to be local, this accretion luminosity can also actually stop material that is in the process of falling in already (stuff that hasn’t gotten to the event horizon yet). It’s all about how the kinetic energy of the infalling material is changed.

Finally, the growth of the SMBH into an UMBH also means that any outflow from the black hole will be bigger and badder. In general, the material flowing away from SMBH’s flows out, cools, and some of it condenses into stars or flows back in as accretion. Once the outflow get’s big enough, it becomes a superwind and no recycling of material takes place – bye  bye gas.

So, in our reality, black holes have an upper limit that comes basically from the fact that things spiral in and the material spiralling in does destructive things: Blasting Light, Blasting Wind. Blame angular momentum and if you want to build a bigger blackhole, get good at aiming stars.

So here is the paper. On a quick read, this is just another paper on what happens to gas when and star formation when an AGN gets involved. If you’ve listened to many episodes of Astronomy Cast, you might have heard me explain this before. AGN (short for Active Galactic Nuclei) are actively feeding black holes in the centers of galaxies. These giant monsters are capable of calmly devouring vast quantities of gas and dust with accretion rates (the rate they take stuff in) of anywhere from 1 to 100 Solar Masses a year. AGN can occur in all sorts of different galaxies, and once upon a time, our own Milky Way galaxy might have had one in its core. Spiral galaxies with lots of gas and dust can recover from their AGN phase to go on to billions of years of happy go lucky star formation. Elliptical galaxies aren’t so lucky.

If you look out at the sky with a reasonably large telescope and you explore the distribution of colors and shapes of galaxies, you’ll find that spirals are generally (but not always) blue, and elliptical galaxies are generally (but not always) red. Any of you who have played with Galaxy Zoo have probably seen this too, and cursed your fair share of boring red blobs. The only way to get a blue galaxy is to look at a system that contains lots of hot stars, and hot stars don’t live that long, so either you are looking at something with ongoing star formation or something that produced stars until very recently. This tells us that in general, spiral galaxies are actively forming stars, and ellipticals are not. As we look at these systems across other wavelengths, looking for gas and dust using Infrared and radio and all the colors of light in between, we also find that elliptical galaxies are poor in gas and dust and spirals are rich in those exact same things. This means ellipticals generally just don’t even have the stuff in them necessary to form stars.

The question is, how did they get that way?

The standard answer has always been that there is a burst of star formation (often triggered during the formation of the elliptical, or the merger of a spiral galaxy into an elliptical), and the gas and dust not involved in this sudden burst is driven into the super massive black hole in the center of the system (and when I say super, I mean something 10,000,000,000 solar masses or so in size!) This process causes the galaxy to first light up with star formation, then the AGN turns on, and in the end the AGN is all that is left signaling the recent event. The timescale for this process was originally thought to be determined largely by the rate of star formation, but star formation is a slow thing, with many billion years being required to eat away the gas and dust. But… with timescales that long we should see more blue(r) ellipticals. The longer something lives, the more likely we are to see it. (Think of being in a room with a variety of lights that randomly turn on and off that are on all sides of you. Those that turn on for the longest period of time are the ones that you are most likely to see, while those that flick on the smallest fraction of a second are very unlikely to be something you see well enough to learn anything about them.)

So here we were with a model and a universe that weren’t in perfect alignment.

But then came this paper, to tell us we had underestimated the effects of an AGN. In this paper, they look at a series of 24 galaxies (10 Star Forming, 10 AGN+Star Forming, and 4 AGN). What they found was about 200 Million years after the Star Forming turns on, the AGN kicks into full swing, and the Star Formation dies quickly – it dies in a fraction of the time predicted from models that use star formation to devour the dust. This indicates that the AGN is having more of an effect on the dust than previously thought.

They put forward in this paper that AGN feedback is responsible for destroying the gas that would have otherwise gone into star formation. This process was already thought to exist, but the magnitude of the role it plays hadn’t been assumed to be this big! It appears that the actively feeding AGN is able to heat and expel the gas very quickly. We knew this happened in GIANT galaxies, with GIANT AGN (think M87), the type of systems that often sport massive jets and other rather radical high energy phenomenas. What we didn’t know was that low luminosity AGN do the exact same thing. And that is just cool. (Or actually “That’s Hot”).

This paper gives us a cleaner insight into how effectively black holes can kill things. That is a very flippant remark, but to put it more scientifically – we now have new insights into how actively feeding black holes can disrupt the surrounding gas so effectively that they shut down star formation essentially instantly (on cosmic timescales at least). From alive to AGN to dead and red in a billion years flat, that may be the life of even the most mundane elliptical galaxy.

While this paper does use a lot of technical language, it explains itself well and is well referenced. If you feel like chewing through something that will hopefully change how we look at ellipticals, give it a read.

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On a completely unrelated note: There is a remarkably ugly huricane on its way to Texas. One of the worst nights of my life involved a tropical storm parked over Houston that caused flooding and tornadoes as far north as Austin (the barn I used to keep horses at flooded and several hundred horses had to be evacuated in the middle of the night with water rising faster then a human could run). Just looking at the satillite imagery is making quesy with anxiety. My heart goes out to everyone on the Gulf coast. Stay safe everyone.

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