Quasars, cosmic evolution, and
what I did on my spring vacation

by Kirk Korista
slightly modified from an article appearing in the Kalamazoo Astronomical Society Newsletter, September 1998

An artist's rendition of astronomers' best guess as to the environs of a quasar (the brightest object at center) situated at the very center of a birthing massive galaxy in the early history of the universe.  (Artist: Martin Kornmesser, STECF)

Besides teaching astronomy classes at WMU and doing some educational public outreach, a good deal of my time goes to doing research. Much of my research is centered around those mysterious beacons of light in the centers of some galaxies known as quasars. First identified by Maarten Schmidt on February 5, 1963, these most luminous long-lived objects in the universe  (gamma-ray bursters emit even more energy, but are very short-lived) are now known to lie in the nuclei of massive galaxies (and so the phenomenon belongs to the class of objects known as active galactic nuclei). Quasars were a much more common phenomenon billions of years ago than they are now - being essentially extinct. Because the universe is expanding with time, the light we receive from a quasar is "redshifted," i.e., shifted to longer wavelengths compared to the light that was emitted by the quasar long ago. Their extreme intrinsic brightnesses allow us to view them to back to the era when galaxies were first putting themselves together. Neither quasars nor galaxy formation is yet well understood. However, evidence is presently building that the quasar phenomenon is intimately tied up in the formation & early evolution of massive galaxies.

Quasars generate as much energy as 10, 100 or even thousands of normal galaxies within a volume roughly the size of our solar system. Supermassive black holes, 100 million or even several billion times the mass of our Sun, are thought to be their powerhouses. A black hole is an entity  whose gravitational field is so strong that not even light, traveling at nearly 300,000 km/s can escape it. Just as energy is made available to crack your bones after falling off your ladder, accelerating in Earth's gravitational field, gas in the vicinity of a black hole will orbit, form a gaseous disk, and slowly fall into the black hole - liberating copious amounts of energy across the electromagnetic spectrum. The process of matter falling into a black hole is far more efficient in the liberation of energy than the nuclear fusion that occurs in the centers of stars. If for some reason the supply of matter flowing into the black hole is cut off, the monster (black hole) will starve, and the quasar will stop shining. It is primarily for this reason that the quasar phenomenon is no longer - quasars had their heyday in the days of galaxy formation and early evolution, because of that epoch's copious supply of (cold) gas to feed the monster.

Before continuing my story, first this side note about black holes...Black holes are not giant cosmic vacuum cleaners as portrayed by Hollywood. If our Sun became a black hole today, virtually nothing would happen to Earth's orbit. It would just get awfully cold around here. Matter spirals into a black hole for mainly the same reasons Skylab re-entered Earth's atmosphere and crashed to its surface. Frictional forces from Earth's heated and expanded atmosphere during a solar maximum episode caused Skylab to lose orbital energy (and angular momentum). And so like a penny that spirals around one of those funnels in museums and zoos loses its energy of orbital motion to friction (more aptly called turbulent viscosity), matter in the surrounding accretion disk will fall into a black hole. Because the penny loses orbital energy, energy must reappear in some other form (conservation of energy), and so it does - in the form of heat and sound emanating from the penny/funnel interface. Now because the mass of the supermassive black hole is large, the orbital velocities are large and thus the energy dissipated in radiation is also enormous. Having said this, it is true that strange things do happen to the orbits of objects very near to black holes. Now, back to my story.

Since quasars are observable over most of the universe (from the near here and recent to the far away and long ago), their potential use as beacons and yardsticks of cosmic evolution has long been recognized. For example, if we could determine their luminosities (intrinsic brightnesses) independent of any knowledge of their distances from us, we could couple this information with the measured or apparent brightnesses to determine their distances. Putting the distances together with their redshifts would allow us an unprecedented measure of the history of the expansion of the universe. A possible breakthrough appeared some 21 years ago (1977) when a young graduate student by the name of Jack Baldwin published a paper which demonstrated that a certain measure of a quasar's spectrum is apparently correlated with its luminosity. The light spectrum of a quasar is composed of two parts: a continuous source of radiation and discrete emission lines. The underlying continuum is evidently emitted by the hot, dense gases orbiting near the supermassive black hole. This radiation is emitted roughly continuously over a very broad range of wavelengths, as in an incandescent light bulb, except that the spectrum extends from X-rays through ultraviolet, visible, and infrared. Some of the continuum radiation is intercepted by surrounding lower density gas and is energetic enough to strip atoms of their  electrons. This process heats this lower density gas (origin as yet unknown). Through collisions the warmed gas excites some of the  electrons still bound to their parent atomic nuclei to high energy levels. In the process of the electron cascading down to lower atomic energy levels, the atom or ion emits photons of light with  specific energies - emission lines. Similar processes occur in our fluorescent and street lights, and these too are emission line sources. Back to the point, Jack Baldwin found that when comparing the brightness of the emission line to the brightness of the nearby (in wavelength) continuum, this ratio was inversely proportional to the luminosity of the continuum. So if this relationship could be externally calibrated, one could measure the emission line to continuum intensity ratio and then know the quasar's luminosity and thus its distance. This created quite a stir at first. However, as more data came in, it was found that this relationship had substantial scatter to it (i.e., for a given ratio, a unique luminosity could not be found). Some of the scatter was due to observational error, and so could be removed with better data, but a significant portion of it was deemed to be intrinsic to quasars themselves. Since nobody knew how quasars worked, this didn't bode well for the "Baldwin Effect", as it had come to be known, in its use as a cosmological yardstick.

Even while most astronomers had long given up on the possibility that the Baldwin Effect would ever tell us something about the history of the universe, observations of quasars continued. And ever so slowly a very fuzzy picture of how they may work has begun emerging from the fog. It is on this front that two of my collaborators, Gary Ferland (Univ. of Ky) and Jack Baldwin, may have hit (or rather stumbled) on a breakthrough. It was in 1993 when Gary was visiting Jack down in La Serena, Chile, headquarters of the Cerro Tololo Interamerican Observatory, Jack's employer. Jack is an observational spectroscopist, while Gary's specialty is the theoretical simulation of spectra. I do some of both. They were working on trying to understand the spectrum of a particular quasar (Q0207-398) and from what kinds of environments the emitted spectrum might arise. The environmental parameters include chemical abundances of the emission line gas, the density of gas particles within and the intensity of the continuum radiation striking the emission line gas, amongst others. One of the great standing mysteries concerning quasar spectra is their great homogeneity despite the factor of ~100,000 range in their luminosities. No other class of astronomical objects seems to share in this characteristic to quite this extent.

One early idea (1982) was that something (a "hand of god", not to be taken literally) somehow fine tunes the quasar environments so that they always produce similar spectra. Theoretical models were developed upon the HOG (hand of god) hypothesis, but many astronomers found them distasteful, being akin to balancing pins. Gary and Jack were amongst these opponents. Jack asked Gary to simulate the spectra emitted by gas from a huge range of environmental parameters (mainly gas density and continuum intensity) in order to best zero-in on the ``optimal parameters'' Gary did this and supplied Jack with the simulated spectra. But in the process of looking at the vast array of simulated spectra and comparing them to the observed spectrum, Jack had a flash of insight. He asked himself, "what would happen if I were to add up the emission from all of the simulated spectra emitted by gas clouds whose characteristics spanned a vast range of environmental conditions?" What the heck, right? What do you think he found? A typical quasar spectrum! At this discovery Jack pulled Gary into his office, showed him the result and exclaimed, "my god, Gary, quasars are just a load of crap!" (pardon the expletive). And so was born a new model for quasar emission line gas, "LOC" for short. We invented an appropriate acronym for the journals: "Locally Optimally-emitting Clouds." The way this works is akin to Darwinian natural selection - nature selects, from a vast population, those clouds best suited to emitting the light we see. This represents the very antithesis to the early HOG model. My gut feeling is that nature operates somewhere in between the HOG and LOC hypotheses, like organized chaos. Time and research will tell.

So it was that my two collaborators and I decided the time was right to organize a meeting on the "Baldwin Effect". We would invite some of the biggest researchers in quasars and establish the level of our understanding of them and determine whether or not the Baldwin Effect could ever be used to decipher the evolution of the universe. We would hold the meeting in La Serena,  Chile where the young Jack made the discovery. Being naturally humble, Jack is embarrassed to have  his name attached to this effect, so the meeting did not have "Baldwin Effect" in its title. We also wanted an outsider's perspective. A bunch of people standing around nodding their heads in the same direction rarely solve any problems. So we also would invite some leading observational cosmologists, including two of the guys who are part of the team of astronomers measuring the light of a class of exploding stars known as supernovae type Ia's, and finding that  the universe may be accelerating. In all about 30 astronomers attended the informal workshop - the best setting to exchange ideas. Gary and I went down a week before the meeting to work with Jack on our related research, so I spent a total of 2 weeks of May in Chile. The week-long  meeting in mid-May was a great success in that much was learned by all and we have collectively set out on a course to compile and observe a properly chosen sample of quasars. Once analyzed, the spectral characteristics of this sample should tell us about the evolution of quasars and  possibly some aspects of the evolution of the universe through the Baldwin Effect. I gave a talk which described a hypothesis for the origin of the Baldwin Effect. It also seemed to answer many other questions still remaining in people's minds, and I received a lot of positive feeback.

In addition we all toured the Cerro Tololo Interamerican Observatories and the site of the new observatories of Gemini South and SOAR on Cerro Pachon, all in the lower mountains of the Andes. The dome of Gemini South (8-meter mirror) was roughly 70% completed, while SOAR was still just a hole in the ground. If they find the money, Michigan State University is slated to be a partner in SOAR, along with NOAO, Brazil, and the University of North Carolina (by coincidence the last place of employment of WMU's new president). The views from up there are just gorgeous, in many ways more beautiful than those from Las Campanas further to the north whose beauty I described in my last letter as stark, like the boulder fields of Mars. A whole lot of building is going on in Chile at the moment. In addition to Gemini South and SOAR (4.2-meter wide field, adaptive optics) are the VLT (four 8.2-meter meniscus mirror telescopes in an array) and the twin Magellan project telescopes (two 6.5-meter spun-cast mirror telescopes). It had not become dark until we had come down from the mountains, but still we were in the midst of complete isolation, and we stopped to get out and look at the skies.  The Magellanic Clouds were spectacular to see even with just the naked eye. Orion was setting up-side-down, depending upon how one viewed him, in the west.

Three days after my return, I took my family to Scotland for 3.5 weeks. Another collaborator of mine (Keith Horne) working in the fields of quasars and a class of stars known as cataclysmic variables is an astronomer at the University of St. Andrews. It's located in (guess) St. Andrews, a nearly 1000 year old town founded by a monk named St. Rule, who carried with him the bones of St. Andrew to Britain and was shipwrecked at the site of the town, or so the legend has it. A beautiful town on the east coast, it comes complete with ruins of a castle and cathedral. At a latitude of 56 or so degrees north, the Sun set at about 10 p.m. and rose at about 3:30 a.m., and never got all that dark. So not much observing of the night sky could be done. My family toured much of Scotland by foot, bus or rail, while I worked. What a deal! Well, I did get out to hike some Scottish highlands and a few other sights on the weekend. Of course, as Americans, we were drawn to see the monuments of "Braveheart" (William Wallace to the Scots) near Stirling Bridge and their great hero Robert the Bruce near Bannockburn. Both were sites of great Scottish victories over armies of overwhelming numbers of English. While we were visiting Bannockburn, a large number of Scots were rallying for Scottish independence from Britain. For some the fight still goes on. Of course, my wife and boys visited Loch Ness, determined to get the definitive photographs of the beast. We have them and will be selling them to the National Enquirer for $1 million a piece. Castles were a plenty as were ancient village sites, burial chambers, and huge standing stones in circles.  We all got up to see Skara Brae, in the Orkney Islands, a well-preserved 5000 year old stone village. Scotland is beautiful, sometimes beyond words. The people are outgoing and openly friendly; just don't get in their way during the World Cup tournament...I highly recommend it.

And so, in the words of a particular farmer who owned a particularly famous pig, "that'll do."

Kirk T. Korista
(now) Professor of Astronomy
Department of Physics
Western Michigan University
Kalamazoo, MI 49008-5252
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