by S. Prasad Ganti
Eminent astronomer Dr. Maarten Schmidt passed away recently. His greatest discovery was an esoteric astronomical object called a Quasar. He appeared on the cover of the Time magazine in 1967 for brilliantly solving a part of the mystery. It took me a while to understand at a high level what a Quasar is. Here is my understanding of Dr. Schmidt’s work.
In the 1960s, very intense radiation at radio frequencies were received on the earth. They were detected by radio telescopes which are a bunch of antennas and radio receivers hooked up to each other. There was corresponding radiation at visible frequencies too, detected by optical telescopes, but that was too feeble. The radiation at radio frequencies did not fit the pattern of any known star within our galaxy or any from other galaxies. Dr. Schmidt found that this radiation is extremely red shifted, which means that the original source is moving away from us at very high speeds.
As Edwin Hubble found that our universe is expanding rapidly. That is the galaxies distant from us are moving away from us even faster. When radiation from such objects reaches us, it is red shifted. Meaning that a blue object moving rapidly away from us appears as a red color to us on the earth. If the speed is much more, then the radiation moves further down from red into the invisible frequencies like infrared and radio waves. Like the siren of an ambulance changes in pitch as it moves away from us.
The radiation from a Quasar would have started its journey as visible light, but over the course of billions of years, it moved to radio frequencies and appeared as such to us. Since the intense radiation was at radio frequencies the source was named as a Quasar (Quasi Stellar Radio Source). The name symbolized the mysterious nature of the source from where this radiation was coming from.
Because of the extreme red shift, it was postulated that the source was very very far away from us. It is not from our galaxy or our local group or our supercluster of galaxies. It is clearly coming from extreme distances across our universe. And looking that far out into the universe means that we are looking back in time. Because radiation takes time to traverse vast distances across the universe, Quasars are from the earliest life of our universe.
A key question is how could we have had such powerful sources of radiation so early in the life of our universe. What powered their luminosity? Now it is agreed that quasars are powered by black holes which exist in the middle of distant galaxies. Super massive black holes are known to exist in the middle of every galaxy. But how did black holes form in such early stages of the universe? Stars were just forming, so there could not be corpses of stars. Latest theory is that huge masses of cloud and dust directly collapsed into black holes, instead of going through the star formation process and their subsequent deaths.
As matter falls into a central black hole, it grows bigger and bigger. Emission of radiation resulting from a star which ventures close enough to a black hole, is the most likely explanation for a quasar.
Quasars were much more common in the early universe – about 2 and 3 billion years after the Big Bang. Accordingly, most distant quasars are from 8-10 billion years ago. Do they exist today ? We will not know for another 8-10 billion years. There will always be this lag of when an event occurs in the distant parts of the universe and when we get to observe it.
We do not see any quasars closer to home. If we did, it would outshine our sun hands down. Something like a cosmic fireworks called supernova does not happen anywhere in our neighborhood. If it does, we would be history in no time.
Dr. Schmidt was a giant who helped us peer into the distant stretches of our universe and helped us go back so much in time when the universe was a lot younger. My kudos to him for his great achievement. And the quest for the exotic astronomical objects continues.