The threshold for quiescence is somewhat arbitrary, but several authors place it at < 10^-11 stellar masses worth of stars /yr. For comparison, the Milky Way produces about 3 stellar masses of stars per year (and the Milky Way is on its way to quenching).
The scale factor of the universe, a, is defined as 1 for the present universe and is used to relate the scale of the universe at different times (and is directly related to redshift, since looking out is looking back). For instance, a = 0.5 would be the time when the universe had half of its present size.Age wrote:So, to you, the alleged acceleration of expansion of the Universe is caused by any energy density with a negative equation of state that does not scale with scale factor of the Universe, correct?Astro Cat wrote: ↑Thu Jun 30, 2022 12:57 pm Quenching is associated with a lot of different aspects of galaxies such as their morphology (spheroid vs. disky), Sérsic index (drop-off in intensity as a function of distance from the center), AGNs (active galactic nuclei, e.g. their black holes), etc. We observe a buildup of high stellar mass spheroid galaxies with low specific star formation rates at lower redshifts (so, more recent in cosmic time) than at high redshifts, but it's tough to discern what common features of quiescent galaxies might have a causal role in their quenching or what features result from quenching.
Dark energy is any energy density with a negative equation of state that doesn't scale with the scale factor of the universe. It drives the acceleration of cosmic expansion
If this is correct, then what is the scale factor of the Universe, exactly?
For instance, if we look out to redshift z = 1.1, we see the universe as it was when it was a little bit less than half of its present size:
a = 1/(1 + z) = 0.476
We can actually see the effect of this at the point of angular diameter turnaround. Funnily enough, the best way I've ever seen to describe that is with an xkcd comic (which I've absolutely included in slides I've used on the topic, LOL ^_^):
Energy densities with a positive equation of state (w = 1/3) and scales by /a^4 is simply radiation.Age wrote:True?
So, what does the energy density with a positive equation of the state that does scale with the scale factor of the Universe actually do, exactly?
Energy densitites with an equation of state w = 0 and scales by /a^3 is matter.