Supernova IA Assumptions
Supernova type IA events are considered a critical standard candle. The observed light curve is assumed to allow a direct calculation of its distance.
This assumption was used in a 1998 study which resulted in the 2017 Nobel Prize in Physics, for confirming the accelerating expansion of the universe.
I posted about this study on August 26, 2019. This post follows up with more detail about supernovae. Most quotes are from Wikipedia.
Supernovae are rare:
Only three naked-eye supernova events have been observed in the Milky Way during the last thousand years. The most recent directly observed supernova in the Milky Way was Kepler's Supernova in 1604.
Observations of supernovae in other galaxies suggest they occur in the Milky Way on average about three times every century.
The one before 1604 was in 1572.
With the last one over 4 centuries ago this expected rate of 1/33yr is inaccurate. None of the expected 12 were detected in this span.
Our galaxy offers a very minimal history.
The most recent supernova IA observed in the universe after 1604 was SN1937C in IC 4182 in the Canes Venatici constellation, but Wikipedia has few details.
The next IA after that one in 1937 was SN1972E in NGC 5253 in the Centaurus constellation, and 'became the prototypical Type Ia supernova.'
Now that astronomers are looking for these IA type supernovae, others have followed (Hubble launched in 1990):
SN1994D in NGC 4526 in the Virgo constellation,
SN2002bj in NGC 1821 in the Lupus constellation,
SN2003fg in 'anonymous galaxy' in the Bootes constellation,
SN2004dj in NGC 2403 in the Camelopardalis constellation,
SN2009-MENeaC in the Aries constellation(this one was observed in a globular cluster near an anonymous elliptical galaxy in a cluster at a distance of 1 billion lyr),
SN2010lt in UGC 3378 in the Camelopardalis constellation.
Since 1972 defined the prototype for IA, only 6 have followed.
This is an interesting diversity including associations with anonymous galaxies, even one within a globular cluster.
Theoretical studies indicate that most supernovae are triggered by one of two basic mechanisms: the sudden re-ignition of nuclear fusion in a degenerate star or the sudden gravitational collapse of a massive star's core. In the first class of events, the object's temperature is raised enough to trigger runaway nuclear fusion, completely disrupting it. Possible causes are accumulation of sufficient material from a binary companion through accretion, or a merger. In the massive star case, the core of a massive star may undergo sudden collapse, releasing gravitational potential energy as a supernova. While some observed supernovae are more complex than these two simplified theories, the astrophysical mechanics have been established and accepted by most astronomers for some time.
The two simplified theories involve a disruption in the fusion cycle.
The massive star releasing 'gravitational potential energy' to become a supernova makes no sense.
Work can be done on a body lifting it a distance in a gravitational field.
The body is said to have gravitational potential energy in that state.
When the body is released it moves at free fall acceleration toward the body with this gravitational field.
after the body is released, that gravitational potential energy has no affect.
gravitational potential energy is most useful for calculating the escape velocity from the earth's gravity.
In the suggested massive star scenario, part of the star has somehow separated, is being held apart, then released to accelerate in free fall toward the larger portion resulting in a violent collision, observed as a supernova.
This substantial internal separation cannot be possible in a massive star under such extreme density and pressure to sustain fusion.
No explicit mechanism in a supernova is suggested other than 'runaway nuclear fusion.'
Any use of 'runaway' means this proposal violates known physics.
From the 1998 paper (linked in that 08/26/2019 post; only a few excerpts are needed here):
To understand how the studies deal with the questions of supernova evolution, it is important to be clear that evolution is not assumed to be a monotonic
function of the age of the universe; in other words, we do not expect that supernovae are uniformly fainter as you study them at higher redshifts. Rather, the main concern is that the typical environment in which a supernova explodes may on average be a little bit different at high redshift from that at low redshift.
A difference in supernovae might coincide with the difference in distance to their galaxies.
Alternately, the environment may affect the supernova, perhaps from its velocity (?).
That coincidence should draw into question the distance calculation.
For example, a host galaxy that has undergone many generations of star formation will have built up a higher density of the heavy elements (the astronomers call this "metallicity"), and one might imagine that this might lead to a supernova explosion of differing brightness. The key point, however, is that different galaxies have begun their life at different times in history, so at any given redshift there will be a wide distribution of galaxy ages, and hence metallicities. The demographics may shift as we go back in redshift, such that the peak of the host galaxy age distribution becomes a little bit younger, but there are still examples of both young and old host-galaxy environments even in the nearby supernova population.
We therefore can study supernova evolution effects simply by looking at nearby supernovae across a wide range of host galaxy ages. For the relatively small samples that have already been studied, the light curve width-luminosity relation appears to account for any evolutionary differences quite well, as we have seen. However, we would like to be able to examine hundreds of nearby supernovae to find even small departures from, and refinements of, this calibration relation.
References to metallicity reveal a search for causes of a disruption in the expected fusion progression.
Clearly the mechanism for a supernova is not certain, with two 'accepted simplified theories.'
Galaxies could have stars with a composition slightly different than in another galaxy, let alone within the same galaxy. The stellar composition is expected to affect the supernova.
After a review of the listed supernova IA detections, recognized as 'the relatively small sample' and with the recognition of the importance of the stellar composition before the event, I question whether the supernova behavior is truly as predictable as claimed.
With that observation, I also question whether the conclusions drawn in the 1998 study were valid.
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