A supernova is considered a candidate for a standard candle, which is an accurate mechanism for calculating a distance by its light dimmed in a predictable manner by the distance to its source.
After some research, there is no basis for this expectation of a supernova.
Claims of an observed supernova must be verified to establish their validity.
This post is long because it has much data to justify the conclusion.
Astronomers have tried to explain this mechanism in a star which results in the observed brightening assumed to be an explosion.
excerpt from NASA:
Supernovae are divided into two basic physical types:
Type Ia. These result from some binary star systems in which a carbon-oxygen white dwarf is accreting matter from a companion. (What kind of companion star is best suited to produce Type Ia supernovae is hotly debated.) In a popular scenario, so much mass piles up on the white dwarf that its core reaches a critical density of 2 x 10^9 g/cm^3. This is enough to result in an uncontrolled fusion of carbon and oxygen, thus detonating the star.
Type II.These supernovae occur at the end of a massive star's lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy. If the star's iron core is massive enough, it will collapse and become a supernova.
However, these types of supernovae were originally classified based on the existence of hydrogen spectral lines: Type Ia spectra do not show hydrogen lines, while Type II spectra do.
Gravity gives the supernova its energy. For Type II supernovae, mass flows into the core by the continued formation of iron from nuclear fusion. Once the core has gained so much mass that it cannot withstand its own weight, the core implodes. This implosion can usually be brought to a halt by neutrons, the only things in nature that can stop such a gravitational collapse. Even neutrons sometimes fail depending on the mass of the star's core. When the collapse is abruptly stopped by the neutrons, matter bounces off the hard iron core, thus turning the implosion into an explosion.
For a Type Ia supernova, the energy comes from the runaway fusion of carbon and oxygen in the core of a white dwarf.
definitions from Wikipedia topic for Supernova:
Type Ia has singly ionized Silicon (S II) absorption line at peak light. Cause is 'thermal runaway.'
Type Ib shows non-ionized helium (He I) absorption line.
Type Ic has weak or no helium absorption line.
Type II-P reaches "plateau" in its light curve.
Type II-L has "linear" decrease in light curve (linear in magnitude versus time)
Cause of all types except type Ia is a 'core collapse.'
Type IA definition has settled, after being 'hotly debated' for a binary pair combination, on only a 'popular sceario' with 'uncontrolled fusion 'for an explanation.
This ill-defined scenario cannot be a good candidate. If unctrolled it is not predictable.
Type II has gravitational collapse causing an explosion as the explanation.
This ill-defined scenario cannot be a good candidate.
Astronomers lack an understanding of a supernova. A sequence of brightening cannot be explained to provide a prediction.
Without a valid explanation of the process, the definition of a supernova is not worthy of 'super' but rather is just a nova, a star whose brightness changes due to a natural process rather than an explosion.
The nova is also unexplained but this topic is about supernova.
These supernova scenarios are not predictable for use as a standard candle.
Despite lacking a basis, astronomers have observed many stars who brightened, called many a supernova and identified a type for that brightening.
Supernova survey systems have been developed to catch a number of 'new' bright stars during the continuous sweep of the sky by automated digital comparisons of images.
The following is most supernovae since roughly 1800.
The list ends here when the events become too dim (to reduce the list).
"no supernova occurring within the Milky Way has been visible to the naked eye from Earth since ."
The problem with all remote supernova is the host galaxy distance will be wrong (by redshift) resulting in a wrong brightness expectation to start with when the baseline is a star in the Milky Way.
Data from Wikipedia list of supernova:
MM or maximum magnitude is from the Open Supernova Catalog when available. The star Vega is 0; 6 is visible to the naked eye; the increasing value is dimmer.
SN1885A was in M31, at 2.4Mly, but is type I peculiar. MM=9.0
SN1937C was in IC 4182 at 13Mly, is type Ia. MM=13.96
SN1940B was in NGC 4725 at 36Mly, is type ii-P. MM=12.8
SN1940A was in NGC 5907 at 50Mly, is type ii-P. MM=14.33
SN1940C was in IC 1099 (no d), is type ii-P. MM=16.3
SN1972E was in IC 3253 at 11Mly, is type Ia. This is considered the protype Ia. MM=7.77
SN1983N was in M83 at 15Mly, is type Ib, the first Ib.
SN1987A was in LMC at 160kly, is type II-peculiar. MM=1.9
SN1993J was in M81 at 11Mly, is type IIb. MM=9.91
SN1994D was in NGC 4526 at 50Mly, is type Ia.
SN1998bw was in ESO 184-G82 at 140Mly, is type Ic.
SN2002bj was in NGC 1821 at 160Mly, is type Ia.
SN2003fg was in unnamed at 4Mly, is type Ia. (no basis for distance)
SN2004dj was in NGC 2403 at 8Mly, is type Ia(SAB).
SN2005ap was in unknown at 4.7By, is type II. MM=12.04 (no basis for distance)
SN2005gj was in NGC 266 at 200Mly, is type II-n for a new type.
240SN2006gy was in NGC 160 at 240Mly, is type IIn.
SN2007bi was in unnamed at 160Mly, is type Ia.
SN2007uy was in NGC 2770 at 84Mly, is type Ibc.
SN2008D was in NGC 2770 at 88Mly, is type Ibc; claimed to be observed while exploding just by its changes in brightness.
Wikipedia has NGC 1770 at different distances.
in 2009: MENeaC was in globular cluster of unnamed galaxy in a glaxy cluster at 1,000Mly, is rated type Ia.(no basis for a distance; it is considered 'associated' with a globular cluster.)
SN2010lt was in NGC 3378 at 240Mly, is type Ia(sub-luminous). (it reached only magnitude +17 so it was very faint; but was type Ia??)
SN2011fe was in M101 at 21Mly, is type Ia. MM=9.48
SN2014j was in M82 at 11.5Mly, is type Ia. MM=8.89
From the Open Supernova Catalog in addition to those above; OSC does not list a distance:
sorted by date:
SN1895B is type Ia. MM=7.07
SN1954A is type Ia. MM=9.1
SN1986G is type Ia. MM=10.61
SN1994D is type Ia. MM=10.96
SN1999da is type Ia. MM=0.13
SN1999dk is type Ia. MM=0.086
SN1999gp is rated IIb. MM=0.006
SN2000ce is rated Ia. MM=0.272
The last few are the brightest in the list.
More sorted by date, but dimmer than above:
SN1989B is type Ia. MM=11.2
SN1962M is type II. MM=11.4
SN1998bu is type Ia. MM=11.44
SN1999ee is type Ia. MM=12.8
SN1999em is type II-P. MM=12.8
SN2000cx is type Ia-Pec. MM=12.9
SN2002ap is type Ic. MM=12.04
SN2003dh is type Ia. MM=12.62
SN2004ef is type Ia. MM=10.32
SN2005cf is type Ia. MM=13.32
SN2006X is type Ia. MM=12.53
SN2007af is type Ia. MM=13.05
SN2008ax is type IIb. MM=12.07
SN2009dc is type Ia-Pec. MM=14.53
SN2009ip is type IIn. MM=12.01
SN2010jl is type IIn. MM=10.62
SN2011dh is type Ic. MM=12.62
SN2012dn is type Ia. MM=13.67
SN2012ap is rated type Ic. MM=12.04
SN2012aw is type II-P. MM=11.96
SN2012ht is type Ia. MM=12.91
SN2012r is type Ia. MM=11.74
SN2013dy is type Ia. MM=12.8
SN2013aa is type Ia. MM=11.28
SN2013ej type II-P/L. MM=11.52
in 2013: IPTF13bvn is type Ib. MM=14.75
SN2014J is type II-P/L. MM=8.98
in 2014:ASASSN-14ha is type II. MM=12.23
there are more with MM > 11.4
object and magnitude
SN1006 -0.8 - recorded around the world
SN1054 -4.0 - recorded in China, Japan, Arabia; is now the Crab Nebula
SN1572 -4.0 - Tycho's Nova
SN1604 +2.95 - Kepler's Supernova
SN1972E +7.77 is is considered the supernova protype for type Ia
SN2010lt +17.0 is type Ia supernova though dim
1) Cosmologists do not have a complete explanation of a supernova event.
Without that, each brightening could be anything else.
2) They rely on only several absorption lines, helium and silicon; both are in the Sun though Silicon is omly 0.002% but present.
3) These supernova types with inadequate detail cannot provide an accurate benchmark brightness to serve as a standard candle.
4) most supernova events since 1680 are dim.
These are claimed to be catastrophic events but none are easily visible.
This suggests a real supernova explosion is as rare as a millenium.
5) They appear to be just a nova, not a supernova which one could expect should be much brighter than a nova.
This spectrum analysis seems inadequate to distinguish between types.
Observed evidence of an explosion is required to verify the selection of an exceptional claim of the unusual supernova..
6) Most are dim so they must be distant regardless of the distance assumed for the host galaxy. The accuracy for comparing the benchmark to a dim object might have a significant margin of error.
The critical driteria for a standard candle are accuracy and consistency.
Only a very small number of actual supernova events occur where a star becomes unusually bright. These include the 4 bright events listed above. All 4 have something visible as a remnant to confirm the brightening was unusual.
The evidence must be provided for each claim. These 4 confirm no others.
Every one of these supernovae having an assigned type must be imaged in X-ray to observe evidence for an explosion.
SN2008D is observed in X-ray to fluctuate. That observation looks like a nova with no debris.
Until that verification is done:
Each event is just a nova or just an intermittent change in brightness, like SN2008D.
The obvious candidate needing verification is SN2010lt; this object was declared a type Ia supernova despite it being only slightly brighter than Eris, a distant TNO!
We are given the unjustified impression astronomers are detecting supernovae.
Unless evidence is provided, many claimed supernovae are probably just nova events. Whatever light curve is observed is not from an explosion.
Until the observed variation in a nova has been suitably explained to be predictable, a variable star like a nova cannot be used as a standard candle.
Just because we can see the Crab Nebula does not mean astronomers know what a supernova actually is.