Back in the 1950s, a group of radio telescopes, probing distant nebulae picked up some radio waves coming from some very distant galaxy. They would come in short bursts, or ‘blobs’ and since the Galaxy was quite far away and the telescopes had a much lower resolution in those times; so it was not possible to pinpoint the source of those waves.
In the late 1950s, making full use of an opportunity, the astronomers were able to pinpoint the area of the sky where this object was located. The moon was passing through the area of the sky where this source could be traced back to; and when the moon passed over it, the signal vanished for a brief period of time. The location was now known.
In 1959, the members of Radio Astronomy Group at Cambridge published the Third Catalogue of Radio Sources, known in short as 3C. This object, though unidentified, was named 3C 273. Upon observing the spectrum of the light emitted by it, Scientists were quickly able to realize that this object was quite small in size, and far, far away. Scientists also make use of something known as Redshift, which is the extent to which the light emitted by an object shifts towards a higher wavelength zone.
New facts and properties of this object (and one other discovered shortly after, known as 3C 48) were being discovered but we were still unable to explain how they were generating such high amounts of energy despite being so small in size. Maarten Schmidt, a Dutch Astronomer working on the Radio data gave two possible explanations for these objects and the fact that they were so luminous. First, that they could be a star, around 10km wide within or near our galaxy. Second, they could be the center of some distant galaxy or galactic nuclei in other terms. The small-sized star idea was highly unlikely, as told by Schmidt himself.
We call them Quasars
But the fact that these objects were so, so bright that the sheer amount of energy they would have to be radiating from so far away seemed impossible to the scientists back then. In 1964, two physicists Edwin Salpeter and Yakov Zel’dovich suggested that the high energy output could be because of the gases in the accretion disk of a supermassive black hole but the idea of black holes was not widely accepted at those times either. However, the math did work out for their explanation. In 1964, American Physicist Hong-Ying Chiu called these objects ‘Quasars’. And this name has stuck with them ever since. Other explanations given during this period (the 1960s-1970s) included being the white hole end of a Wormhole and supermassive gravitational wells among others.
In the late 1970s and early 1980s, however, X-Ray observatories confirmed the existence of black holes and other observations also supported the fact that the high energy output of these objects was indeed due to matter falling into the accretion disk. The fact that these were very far from us was also confirmed and it was concluded that these objects were indeed supermassive black holes at galactic centers.
Properties of Quasars
Today, over 200,000 Quasars have been observed. It has been estimated that Quasars were much more common in the early Universe than today, owing to the fact that the gas and dust clouds had not yet dissipated and hence they could easily fall into the accretion disk of the black holes at the center of the galaxies. We call the supermassive black holes at the center of a galaxy an Active Galactic Nucleus, or AGN in short.
We know today that the Quasars are actually supermassive black holes, ones that are millions of times heavier than the sun. The energy output is due to the gases being heated to millions of degrees. Some of that gas is converted directly to energy and light. While this gas moves around in the accretion disk on its way to fall into the black hole, some of it is collimated into ‘jets’ of hot gases and radiation along the axis of the rotation.
In fact, the orientation of this jet relative to Earth also affects the luminosity of the quasar. If a Quasar is oriented in a way such that its jet directly points towards us, they are called Blazars. In fact, quasars are brighter and more energetic than entire galaxies with their billions of stars. This simple fact gives us a very naive idea of how powerful they actually are.
Sir Lawrence M Krauss, a Cosmologist at Yale, says, “We can observe these from the very edge of the observable universe which means that they existed in the early ages of the universe.” We know today that they were formed right after the first galaxies appeared. The leftover gases flew towards the center of those galaxies and led to the formation of the accretion disks, and subsequent emission of energy.
There are different sub-categories of Quasars as well, such as Radio-loud Quasars, Radio-Quiet quasars, Red Quasars and many others. They are classified mainly on the basis of their spectrum and what wavelength they give off. Quasars, being distant are almost stationary on the sky and are hence used as reference points on the maps of the sky at times.
Quasars are believed to have a role in the formation of the Universe as we see it today. The early universe had plenty of hot gases and it was pretty widespread. This led to the violent formation of massive stars, and their quick and violent demise into supernovae. If life existed back then, it would have been completely obliterated because of the huge quantities of gamma-ray and heat given off by those explosions.
However, the same gases found their way to the centers of galaxies and led to the formation of the earliest Quasars. This era in the timeline is sometimes known as the epoch of Quasars. The Quasars thus formed held on to the gases, slowing down the birth of new stars and in the end, that helped life evolve here on Earth. We, mere specks of dust on a cosmic scale, owe our existence to some of the most powerful objects in the Universe.