‘Energy in stars is produced by hydrogen fusion reactions’
In nuclear fusion the nuclei of light atoms combine at very high temperatures and release enormous amounts of energy that is radiated from the surface of the star as heat and light.
An ordinary star is one of the simplest entities in nature; it is a sphere of gas that is by mass 73 percent hydrogen, 25 percent helium and 2 percent other elements. The temperature in the centre is high enough to fuse four nuclei of hydrogen together to form one helium nucleus.
‘The universe began when a single point of infinitely dense and infinitely hot matter exploded spontaneously. The debris of this explosion began to fly away from the explosion point and is still flying and will keep on flying indefinitely. All the galaxies, stars and planets were formed from this debris’
In 1927 the Belgian astronomer Georges Lemaitre (1894-1966) suggested that at some time in the remote past all the matter in the universe was concentrated at one point. The universe began when this ‘primeval atom’ exploded. This idea was further developed by Gamow, who predicted that leftover warmth from this explosion would still fill the universe. The name Big Bang was given to this theory by Fred Hoyle, who believed in the opposing steady-state theory. It was meant to be a put-down when Hoyle first used it scornfully on a radio talk show in 1950.
‘The universe has no beginning and will have no end. It is constantly producing matter and is expanding’
This theory is now considered flawed and the big bang theory is widely accepted.
The steady state theory includes the idea of spontaneous creation of matter. The big bang theory assumes that all matter that now exists also existed in the past.
‘Most of the elements heavier than hydrogen in the universe are created, or synthesised in stars when lighter nuclei fuse to make heavier nuclei’
The Sun burns, or fuses, hydrogen to helium. This process occurs during most of every star’s lifetime. After a star exhausts its supply of hydrogen, the star burns helium to form beryllium, carbon and oxygen. When the star exhausts its supply of helium it shrinks and its temperature rises to 1000million degrees. The rising temperature triggers a new series of reactions in which carbon, oxygen and other elements combine to form iron and nickel. When the star has burned everything into iron and nickel, it explodes as a supernova. The elements heavier than nickel are formed during supernova explosions.
Hoyle proposed this theory in 1957. Hoyle, along with Thomas Gold and Herman Bondi, had also proposed the steady state theory of the origin of the universe in 1948.