The interior of SK -69 202 just before the outburst is like that of a red supergiant. The core of the star is around the mass of the Sun but is the size of the Earth and composed of iron. The core is surrounded by the shell sources ignited after each phase of core burning ran to completion. The outer envelope of the star is 90 % hydrogen and roughly 10 % helium (as is the rest of the Universe). Because iron is the last element which can be profitably used as fuel for the fusion process, something catastrophic is poised to happen.
Instability
Look at the iron core. It is made out of hot iron nuclei and degenerate electrons. It is supported by degenerate electron pressure and the hot iron nuclei.
Note that as the core contracts in response to the above, the problem is only exacerbated and the collapse accelerates ===> instability.
Core Collapse
Time Scale: The collapse once initiated is very quick. The collapse time is roughly a tenth of a second!
Some Details
The collapse is inside-out in that the denser regions collapse more quickly than the less dense regions. For the star this means that the core collapses in less than a second but that the outer burning shells and the envelope of the star (being less dense) not realizing that the core is gone are suspended above the collapsing core. They do not take part in the event until the explosion begins in earnest.
Neutrinos
A prediction of all models for Type II SN outbursts is that, the dominant source of energy loss is neutrino emission. The star sheds an amount of energy in neutrinos roughly equal to the increase in the energy it gains from the compression due to gravity. This is a huge amount of energy. This is more than 100 times the energy the Sun will radiate in its entire lifetime!
![]() | The Kamiokande and IMB experiments saw around 20 events. Using the information on how far away the LMC is and the difficulty with which neutrinos can be detected ===> that these 20 events are what are expected for a star which collapses and radiates ~ 5 x 1046 Joules in neutrinos -- this is around 5 x 1058 neutrinos at the source (in the LMC) so that ~ 2.4 x 1011 neutrinos passed through every square centimeter of the Earth.The detection of the neutrinos is strong corroboration that our basic model for Type II SN is correct. |
The neutrinos are produced by the core collapse (the initial phase of the SN outburst) and so are expected to lead the optical fireworks by anywhere from hours to days (depending upon the type of progenitor star). The neutrinos led the optical outburst of SN1987A by several hours.
Typical Type II SN are expected to show a lag of several days between the neutrino outburst and the optical display. The short lag is entirely consistent with the fact that SK -69 202 was a smallish blue supergiant and not a humongous red supergiant.