What was the likely host galaxy, supernova spectal type (see Eig. 20.3), and spectroscopic redshift for SN 1969L? Hint: Use the SIMBAD astronomical database [2].
1 Another proposed mechanism involves some aspects of both core collapse and thermonuclear runaway: massive stars of low metallicity can undergo a par-instability supemova, which is described in $\operatorname{Box} 20.2$
2 This is a miniscule fraction of the total diameter. The massive star is typically a supergiant by this time, with its tenuous outer layers spread over a volume that would encompass much of the inner Solar System if it were placed at the position of the Sun.
1. Recall from Section 9.5 .1 that a homologous collapse is "self-similar": it can be described by changing a seale factor.
4 This defines a unit of energy commonly used in supernova discussions that originally was called a foe: 1 foe $=10^{51}$ ergs, with the name deriving from the first letters of fifty-one ergs. This unit is now termed a bethe, in honor of the remarkable plysicist Hans Bethe (19062005), who won the 1967 Nobel prize in Physics for illuminating how nuclear reactions powered the stars and made seminal contributions to many other fields of science, including supernova physics. Bethe (whose name was pronounced the same as "beta") continued to do science until close to his death at age 98 , inspiring a joke that went "The nuclear physicists were wrong; there is no Bethe decay!"
5 The next generation is expected to be exascale systems, with speeds $\sim 10^{18}$ floating point operations per second ( 1 exaflop). The fastest computers available as this is written in 2017 are capable of $10-100$ petaflops $\left(10-100 \times 10^{15}\right.$ floating point operations per second). Optimistically the exaseale for scientific computing could be reached by the early 2020 s.
6 A standard argument was that, assuming the usual model that supemova remnants and lighteurves are the result of a shockwave that disrupts the outer layers of the star after core collapse, the properties of observed bright supernovae in distant galaxies required that the shockwave pass through mostly low-density matter on its way out of the star, and red supergiants are of much lower density than blue supergiants (see Table 2.4) [27]. As will be discussed further below, this was partially observational bias because core collapse in blue supergiants is expected to produce supemovac that are much less luminous than those originating in red supergiants. It should be noted that some theoretical work before SN 1987A considered the possibility that supernovae of lower luminosity might originate in blue supergiants (see [27] for references) but the lack of observational data for such events, and that most stellar evolution calculations of the time favored explosion in the red supergiant phase, caused this possibility to be discounted in favor of the red supergiant progenitor paradigm.