THE QUASARS

( Acronym of "quasi-stellar radio source" )

Certainly the most talked-about discovery of radio astronomy was that of the quasars. The radio source 3C48 which was studied in 1960 by T A Matthews, was found by A R Sandage, by means of an exposure of 90 minutes with the 5-metre Palomar reflector to be a queer type of "blue star". (A blue star is one which has a negative or very small B – V colour index). Its spectrum showed inexplicable emission lines.

Another quasar, 3C273 underwent occultation by the Moon and this revealed it to be a double radio source. The 5-metre telescope found it to possess a faint jet. When M Schmidt studied the spectrum of 3C273 in 1963, he got the brilliant inspiration that the queer spectrum was due to a very large red shift, having a value of 0,16. This meant that it has a recession speed of 14,7% of the speed of light, so that its distance had to be 1400 million light years and thus its luminosity had to be 100 times the total luminosity of an average galaxy !

The optical spectrum of 3C48 could be explained if it was assumed that it had a red shift of 0,37 and a distance of 2980 million light years

An 80 year old photograph showed that the optical brightness of 3C273 was variable with a period of less than one year. It could thus not be as large as 1 light year. How could it then radiate 100 times the energy of a galaxy, at least 50 000 light years across'? The puzzle deepened.

The quasars were found to be strong emitters of ultraviolet light. Fine absorption lines in the spectra of some quasars implied that they have shrouds of gas around them, just like galaxies do.

The bizarre properties of the quasars showed that they are indeed rare birds:

1. Quasars are star-like objects;

2. Quasars are usually strong radiators of radio waves;

3. Quasars are strong emitters of ultraviolet light;

4. Quasars have large red shifts and are thus very far off- 10 to 18 thousand million light years;

5. Quasars are variable in all wave lengths;

6. Quasars have low B – V colour indices and are thus "blue";

7. The activity displayed by quasars is similar to that of Seyfert galaxies;

8. Several quasars are double sources as are several galaxies;

9. The visual light of some quasars is polarised as is the jet from the giant elliptical galaxy M87;

10. The radiation of some quasars increases in intensity with increase in frequency;

11. Some quasars have cocoons of absorbing gas around them, thus showing that they are at the centres of galaxies;

12. Optical spectra show that quasars are in great turmoil. This must be due to series of supernova explosions in their nuclei;

13. The spectra of the quasars show that their atoms are very highly ionised; this must be due to the extremely high temperatures caused by the Supernova explosions.

14. The abundances of elements such as hydrogen, helium, carbon, neon, magnesium, silicon, argon, sulphur and iron correspond to those of many galaxies;

15. The Quasars have spectra with wide lines caused by gases moving at great speeds of 2000 to 3000 km/sec; these gases must come from supernova explosions.

The average visual magnitudes of the quasars was found to be 14 to 19 and their absolute magnitudes, given their vast distances, between -24 and -31, with an average of -28,4. This implies a brightness of 2.512^{4,85 – (-28,4)} = 2.512^33,25 = 2 x 10¹³ times the brightness of the Sun; thus equal to the brightness of ten or 20 billion suns. (1 followed by 13 figures means 100 times 10¹¹ which is the total brightness of the Milky way). No galaxy comes any-where near to the brightness of a quasar. The brightness of the quasars has to be ascribed to something beyond size. Taking this into consideration with their very short periods of variability, means that the only feasible explanation is that the quasars must be galaxies undergoing series of supernovae explosions in their nuclei. This explains both their great luminosities and their short periods of variation.

We see the quasars by the light which left them 10 to 18 thousand million years ago when the universe was very young, i.e. shortly after the cosmo-genesis (big bang).

The first stars that formed in the nuclei of the first galaxies consisted entirely of hydrogen and helium from the cosmo-genesis. In the nuclei of these stars elements heavier than helium were synthesised by the process of fusion whereby protons are fused together. Some mass is lost in this process and it appears as energy. The matter spewed out from the supernovae of the first stars was thus enriched by heavier elements. According to D N Schramm in "The Ages of the Elements" this first series of supernovae took place about 9000 thousand million years ago when the universe was about 4000 million years old. The quasars reveal the story of those events.

After another 4000 million years, about 5000 million years ago the second generation of stars that condensed from the material synthesised by the first generation of stars started going supernova and from the material they spewed out, now enriched for the second time, the third generation of stars, of which the Sun is one, condensed.

The quasars thus tell us the history of the very early days of the universe, a history of great violence.

Jan Eben van Zyl