Video & disscussion on supernovae

Tuesday 15th September, 2015

For our evening talk we were hoping to have Alexander Rigby from Oxford talking to us about "How to make a supernova" but unfortunately car trouble prevented her from reaching us and we had to reschedule her visit for next September. Luckily, we were able to take advantage of freely available resources on the World Wide Web and watched a video all about supernovae.

The video featured well-known scientists such as Prof Michio Kaku and Prof Lawrence Krauss, and we were told how in 1967 an astronomical phenomenon was mistaken for a nuclear explosion leading to heightened political tension. The United States had launched a number of Vela satellites designed to monitor nuclear explosions that contravened the 1963 Partial Nuclear Test Ban Treaty. Luckily, the tension eased when scientists from Los Alamos National Laboratory realised that the intense flashes of light came from outside the Solar System.

The presenters explained that the sudden flash of light known as a gamma ray burst actually came from a dying star that had exploded. This Type 2 supernova was the result of gravity overcoming the pressure from nuclear reactions inside the star. As a star ages it slowly builds up concentric layers, resembling that of an onion, consisting of the heaviest element in the core with progressively lighter elements to the outside.

They then said that at its birth the star would be fusing hydrogen into helium at its core and this process actually releases energy. When it runs out of hydrogen fuel it resorts to fusing helium followed by carbon then neon, oxygen and silicon until it finally ends up building an iron core and the nuclear reactions cease. At this point the star's fate is sealed and it collapses inwards only to rebound off the incredibly dense core. Depending on the star's initial mass the core can either form a relatively stable neutron star only 12 km across or the core may collapse further and form a black hole. Fortunately for us, stars like our Sun do not have enough mass to explode as a supernova and they end their lives as a slowly cooling star known as a white dwarf.

The scientists then said that whereas Type 2 supernovae come from solitary stars that have reached the end of their lives, there is another sort of supernova known as a Type 1 which results from the interactions of a pair of stars that are in orbit around each other. The smaller star is a white dwarf that siphons material from the larger one until it becomes unstable and explodes. As most stars form in pairs rather than singly, these types of supernovae account for most of the iron found in the Universe. Without this vital element our civilisation would not be able to construct buildings and bridges and iron is even found in our blood in the form of haemoglobin which is vital in the transport of oxygen around our bodies.

The commentary then referred back to Type 2 supernovae saying that the more massive elements beyond iron were produced in these events. In fact the gold in wedding rings and electronic circuits began life in these huge explosions far in the deep reaches of space. The Hubble Space Telescope has captured many of these deadly yet picturesque blasts such as the Crab Nebula which was recorded by Chinese astronomers in 1054.