Kirk Korista and the Mystery of the Quasars

November 16, 2019

 

Kirk Korista recalls that when he was born in February of 1963, one of the most perplexing mysteries in astronomy was starting to unravel. More than a half-century later, the Western Michigan University Professor of Astrophysics now contributes to further understanding of what have turned out to be most intense producers of radiant energy in the universe.

 

When Korista came into the world, I was a student at the University of Michigan. One of the buzzes in the astronomy department in the early 60s concerned a relatively new breed of celestial objects that radiated intense energy as radio waves, but appeared as merely fuzzy stars through optical telescopes. The cumbersome designation “quasi-stellar radio sources" was initially used to describe them, later shortened to the now familiar “quasar.”

 

In a recent phone conversation, Korista filled me in on the fascinating story of how the first correlations of the radio quasars with visible objects took place, and of the challenges that ensued in an effort to understand something that at first seemed unbelievable. His account brought back memories of my initial encounters with this very hot subject while in college.

 

That first unambiguous optical source was found with the Mount Palomar 200-inch telescope (then largest in the world) in the early 60s. A spectrum formed by dispersing its light into its component colors was perplexing until astronomer Martin Schmidt came to the startling realization that familiar spectral features were highly shifted toward the red end of the spectrum, indicating that the quasars, whatever they were, were moving rapidly away from the earth.

 

A colleague of Schmidt’s came to the Ann Arbor campus to do a presentation, and I recall that he supported Schmidt’s argument that the great redshift occurred because the quasars were near the very fringes of the expanding universe, billions of light years away. The visiting astronomer admitted that it would be hard to explain how an object so far away, with an apparent size indicative of a giant star rather than a whole galaxy of stars, could be seen at all across such an abyss. From a small area, it had to be radiating energy exceeding that coming from all the stars in the Milky Way combined, an incredible scenario.

 

Vigorous debate ensued as other astronomers argued that the quasars are instead highly energetic stars within the Milky Way moving rapidly away from earth. Being much closer, a far less prodigious source of energy would be required to explain their apparent brightness.

 

When Korista arrived at the University of Illinois in the early 1980s to do his undergraduate work, his mentor was legendary Professor Jim Kaler, who had a high interest in messages contained in the spectra of stars,  galaxies, and also the still enigmatic quasars. The experience with Kaler inspired Korista to make quasars a subject of special interest, especially a further understanding of messages encoded within their complex and still perplexing spectra. Following graduate studies at Ohio State University, post-graduate work at the Carnegie Observatories in California (including use of the Palomar Telescope that found the first optical pulsar), and two decades at Western Michigan University, he continues the quest.

 

It has become clear that quasars do indeed lie far out among and within the most distant galaxies and are not flying around in our home Milky Way. By the dawn of the 21st century, astronomers had determined unambiguously where the quasars are, but still could not explain what they are. How do you account for an energy output equivalent to that of multiple galaxies coming from a volume of space equivalent to that of the Solar System?

 

By then, there was also a better understanding of another mysterious and exotic phenomenon, black holes. Most are stars that were once very massive–much bigger and hotter than the sun–that eventually collapsed, exploded, and then left behind an ultra-dense remnant. That stellar corpse is so dense that nothing, not even light, can escape its gravitational grip. However, gas from nearby stars being torn apart and falling into the ever-expanding black hole will heat up and become luminous, and the greater the rate of in-fall, the greater the luminous power generated. “As the black hole grows in mass, the more powerful it becomes, as long as it is fed,” Korista said.

 

He explained that it is now widely accepted that the quasars lie at the nucleus of very massive galaxies. In fact, they are now more frequently referred to as “active galactic nuclei.” “Their incredible luminosity arises from energy released by the in-fall of matter from surrounding stars and gas clouds into a central black hole millions to billions of times the mass of the sun.“

 

He further explained that because quasars are at such a great distance, they are part of a much earlier episode in the history of the universe, when star formation in newly assembled galaxies was going on at a prodigious rate. That high population of stars provided ample food to keep the quasar shining. “All large galaxies are now known to have super massive black holes in their centers, with a mass that is proportional to the total mass of the whole galaxy. The story of the cosmic evolution of the quasars, and the birth, assembly and maturation of galaxies is all tied together,” he said.

 

I asked about the presumed black hole at the center of our own galaxy and if it will one day grow enough to ignite a pulsar. He explained that there is too little in-falling matter for that to happen. “We are part of a galaxy that formed in a quieter, lower-density region of the universe, and at a later time. That might have been a lucky thing for us!”

 

As our conversation concluded Korista noted, “We now have a broad outline of what quasars are and how they work, and what their role has been in the evolution of galaxies. But we still need to fill in the details, and that is what I find fascinating.”

 

 

 

 

 

 

 

 

 

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