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Maybe not the same brightness over time?

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Maybe not the same brightness over time?
Why is that cosmologists are happy to use the "dark" concepts rather than to suggest that Type 1a supernovae might exhibit different properties over time?Because arguing that type 1a stars have different energy outputs at different times is more of a stretch than the presently accepted explanation. Remember Occam's Razor, the notion that the simplest explanation tends to be the right one. Dark Energy is a simpler explanation than arguing that stars with the same spectra and properties have different absolute luminosities at different times.

The spectra of the stars hasn't changed, and this argues that they have the same composition over time. The fact that they are type 1a argues that they are in the same mass category and have the same history and genesis — therefore the same absolute luminosity.
I have always wondered why stars have such widely differing masses - for I assumed the start process for a star would occur at particular aggregations of Hydrogen. The answer must be due to aggregation of stars.Not likely. Once a star has formed and begun fusion reactions, its energy output drives the surrounding cloud of gas and dust away (or the gas and dust commences to orbit the star). This is a process we can see in areas where stars are being formed — once a star begins to emit energy, it reorganizes its neighborhood. So stars don't accumulate much mass after they are formed, except in some cases by being in a close orbit with a companion star, a well-understood pairing.

In short and in general, stars aren't likely to aggregate into larger stellar bodies after they have formed. Also, if two large stars were to somehow combine, and they had a total mass three times or more that of our own sun (and if a few other conditions were met), they would likely collapse into a black hole.

There are many kinds of stars of widely differing masses, but these differences can primarily be traced to the conditions of their formation, not normally by way of joining two or more stars together.
It may be that the properties of a star going into "supernova" mode depend very much on what exists around it.For supernovae in general, yes, but that is a large category with a lot of variety. For type 1a stars, those conditions are well understood.When the Universe was smaller,I think you want "younger" here, not smaller. Remember that many cosmological models postulate that the universe is infinite in extent. As to the question of how an infinite universe can expand, imagine an infinite array of 1-cubic-meter boxes. The array of boxes extends infinitely in all directions, and each of them is a cubic meter. Now imagine doubling the size of all the boxes, without changing the size of their contents.

An infinite space can be subjected all sorts of ordinary geometric manipulations, once we get over the hurdle of thinking about infinities.
perhaps other stars got involved in such massive events and so the light output of the supernova would vary.For supernovae in general, there is a lot of variation, but those are not all type 1a stars, which have very specific properties — their energy output is reliable and consistent, along with their spectra. as explained here:

Birth of a Supernova

A quote: "Because Type Ia supernovae always explode at 1.4 solar masses, they all have more or less the same characteristics, including how brightly they shine."
Basically, what I am suggesting is that older supernovae would have been brighter than more recent ones. If individual stars can vary in mass then so could supernovae.Yes, but not type 1a, which are created under very specific conditions.

This argument requires an explanation that specifies how the supernovae change over time, and how this causes their brightness to change. Such an explanation is harder to craft than the idea of Dark Energy, granted all the problems posed by Dark Energy.
How does the theory of Fred Hoyle on stellar evolution line up with the use of a supernova as a standard of luminosity?These ideas move along different, but complementary, tracks.
 

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