All of the red dwarfs would still be around-- They have lifespans much, much longer than the age of the Universe so far. Even our own Sun has a lifespan that’s close to that long. It’s just that, in a young, active galaxy with lots of young, hot stars, the red dwarfs will add a negligible amount to the total light of the galaxy, so we don’t see any of them.
Mostly just based on that being the simplest assumption consistent with the error bars. The data actually does (weakly) suggest that it’s increasing.
This is true - however, red dwarfs that are 13 billion years old seem to be rare in our own galaxy, so I suspect they were rare in these galaxies as well, 13 billion years ago. Most stars in that era were large balls of almost pure hydrogen.
I’m not sure we can even determine the age of a red dwarf, beyond what generation it is. And just determining that it’s second generation won’t necessarily mean much, given that the first generation could have lasted less than a million years.
I would think it is neither adding nor subtracting to the total energy of the system.
Consider a box with X-Amount of energy in it. Making the box bigger or smaller does not change the total energy in the box (ignoring outside influences).
But it’s not just a box, it’s spacetime. The material in the box is expanding too, not just the walls.
It is adding energy, just such a minuscule amount that it’s below even theoretical measurements.
Technically, the gravity that the Earth feels going around the Sun is reduced by the expansion of space between them, it is as if the Sun is slightly less massive than it actually is. But that amount is, as I said, minuscule. The math has lots of exponents to it on all sides, so I’m not going to do it, but it’s probably the equivalent to the Sun having a couple less protons in it than it actually has, maybe less than that.
Anyway, the point is that it is not really energy that is being added to the system, any more than the gravity that keeps us in orbit changes the energy of the system. The force from dark energy is constant (over reasonable timescales at least, and maybe entirely).
I believe the balloon inside = past / outside = future is a good, easily understood analogy so long as you keep in mind that inside and outside the balloon simply means just the periphery of the balloon not the air in the balloon (just imagine the air doesn’t exist). Before you inflate the balloon, it’s very tiny with no air in it. This is analogous to the singularity. As you inflate the balloon, it gets bigger and older…until it pops, or deflates back to a singularity/tiny balloon. There is no center or privileged frame of reference on the surface of a balloon as there is none in the universe.
…now, if the Universe is an animal balloon, or has a neck tied by a string, then all bets are off. Untying the string will cause the universe to go pbbbbbbt! and scoot haphazardly across the multiverse. You don’t want that to happen!
This references the ‘crisis in cosmology’ around the Hubble Constant. We have several methods of measuring the expansion of space: Type Ia Supernovas, Cepheid variables, and the CMB. All three methods are well tested and considered accurate - and they all disagree with each other. For a while the different values were within the error of measurement, but they no longer are. Still they are close enough that it may just be a lack of understanding of Supernovas of this type or some other measurement error we haven’t found or something. Again, hopefully Webb to the rescue.
Also, light from red dwarfs would be red-shifted out of our ability to see for the most distant galaxies. It’s the ultraviolet from the star forming and bright young stars that are now red-shifted into JWSTs view. Luckily, the early universe is estimated to be full of gigantic short lived stars that glow in the ultraviolet. It’s the ultraviolet light that caused re-ionization of the hydrogen gas in the early universe, making it transparent to light and ending the dark age.
Calling the center of the balloon the past makes the analogy less bad, but then the problem is that the analogy already includes time in it, represented by time, because we’re talking about the balloon inflating. We end up saying both that the past represents the past, and that the center of the balloon represents the past. If you’re going to commit to an analogy where the center is the past, then you don’t have an inflating balloon any more; you have an unchanging solid ball of rubber, with a bunch of radial spokes representing galaxies.
One way to find the age of a red dwarf is by its metallicity, which gives large error bars but allows astronomers to detect the very oldest stars. Here’s 2MASS J18082002−5104378, which has a metallicity ten thousand times less than the Sun.
Whereas I see the face of Alf in the leftmost pillar.
@eburacum45 , that’s why I said “beyond what generation it is”. A star with a metallicity that low must be a first-generation star, but we can’t tell beyond that, because a red dwarf won’t produce any metals.
(note for anyone who doesn’t know: To an astronomer, “metal” means “any element heavier than helium”)
However, even a red dwarf is formed from the ambient interstellar medium, and from the gas and dust in that medium; the amount of metals in the ambient medium is increasing over time. A red dwarf formed ten billion years ago will contain less ‘metals’ than one formed four billion years ago, and so on.
The metallicity of the interstellar medium is increasing because of generations of stars forming, fusing metals, and then dying and dispersing those metals.
That said, the boundaries between stellar generations can be somewhat fuzzy, since not all stars have the same lifespan. As soon as the very first stellar death, whenever that was, the ISM was slightly enriched in metals, then more so when the second star died, or the tenth, or the ten millionth.
