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Spectroscopic Atlas for Amateur Astronomers 115
25.4 Explosion Scenario "Core Collapse"
The core-collapse-SN forms the end of all stars with >8 M . This theory was proposed by
Fritz Zwicky in 1938. At the end of the giant stage, increasingly heavier elements are gen-
erated in the core of the star. Finally it will be fatal for the star, when it starts to produce
iron. For the formation of this, and all the following even heavier elements, the fusion proc-
esses consume energy. Thus, due to lack of radiation pressure, the core can no longer re-
sist the gravitational forces and therefore it inevitably collapses. This initial implosion is
then quickly changing in to a cataclysmic explosion and at the very end it remains an ex-
tremely dense object with just a few km in diameter. Depending on the original stellar mass
either a neutron star or a black hole is formed. During the core-collapse, the very rare, ex-
tremely large stars of the Wolf Rayet type can further eject a highly intense gamma ray,
headed parallel to the stellar rotation axis (Gamma Ray Burst). In extreme cases it may oc-
cur a hypothetical Hypernova such is expected for Eta Carinae. The physical effects of the
shock wave within the expanding SNR are described in sect. 28.
25.5 Explosion Scenario "Thermonuclear Carbon Fusion"
This scenario is also called thermonuclear explosion and is exclusively limited to the
SN type Ia with an initial stellar mass of <8 M . As a member of a binary system, a White
Dwarf (sect. 24) by accretion of matter and finally exceeding the critical Chandrasekhar-
mass limit (ca. 1.4 M ), may explode as SN type Ia. However as an additional condition a
minimum rate for the annual accretion must be exceeded (߂݉/ > ݎܽ݁ݕ1 ∙ 10ି଼ M ) [297],
otherwise mostly just recurrent Nova explosions occur. However, such much smaller events
are limited to the currently accreted material at the stellar surface, in which the star itself
will not be destroyed. But if all conditions are met, the degenerated electron gas can no
longer withstand the gravitational pressure and the stellar core, mostly consisting now of
carbon and oxygen (C/O), explodes. This cataclysmic event is caused by the sudden onset
of nuclear carbon-fusion, which is why SN Type Ia is sometimes also referred as Carbon
Detonation Supernova. Anyway in contrast to the Core-Collapse SN, SN Type Ia leaves no
residual object.
25.6 SN Type Ia – Standard Candle
As already mentioned the SN type Ia exclusively occurs with White Dwarfs if they exceed by
accretion the "quasi standardised" critical Chandrasekhar-mass limit of about 1.4 M . Thus,
this way a more or less uniform amount of energy of about 10ସହ J is released [295]. Further,
both the photometric and the spectral profiles of such events are very similar. With
SN Type Ia the luminosity reaches the maximum after about 20 – 30 days, with an absolute
magnitude in the blue region of MB ≈ –19.5M [296]. These values remain within just a small
stray area and are, for SN explosions, clearly in the region of the top rankings, which is
bright enough to outshine an entire galaxy for several months. Due to this uniform appear-
ance the SN Ia explosions serve also as indispensable "standard candles" for measuring the
entire observable universe.
For this purpose the core-collapse SN types are less useful, because the intensity of such
explosions depends strongly on the initial stellar mass. The absolute maximum brightness
lies here within a very large stray area of MB ≈ –15M to –21M, see [296, Fig. 2]. The ex-
treme values are denoted here as sub luminous and over luminous [296].
25.7 Spectral Determination-Diagram for the SN Type
The following diagram is used for the spectroscopic identification of the SN type. In addi-
tion, the relevant explosion scenario, the type of the progenitor star, and finally the rough
order of magnitude for the original stellar mass are assigned here.
