Astronomers just confirmed the most ancient galaxies ever observed

I love astronomy since I was a kid. It is amazing how much we've figured out and still doing so everyday. However, I realized this long ago (in my teens) that much of the stats, eg numbers of stars/planets in the universe, their distances/compositions/ages etc, while calculated, are built on top of multiple instances of approximation/assumption/insufficient data. We know very well how a simple early rounding can lead to widely different end result in a chain of equations. Imagine that in a gigantic situation. In my teen years, I've always wondered why they are not launching Hubble 2.0 3.0 etc every 5 years. Because that's what we need. More state of the art observatories out there in space to gather more data. Without that, we're just increasing the chain of assumptions and approximations.

> Can someone here ELI5 how they can be absolutely confident of these distances?

The way I read it is that they're absolutely confident of their fantastic young age, that is, their redshift.

As you point out, the age-to-distance conversion isn't quite settled, but that doesn't really matter in this context I think, as younger will still mean further away.

So these galaxies will still be the furthest away (for now) even if the distance ladder gets adjusted "inward", ie closer to us.

> Can someone here ELI5 how they can be absolutely confident of these distances?

In physics, it is common for the writing to say that some fact was "shown" or "proven". Maybe look at the "absolutely confident" as similar!

I'm a skeptical and often dissatisfied reader of the fundamentals in physics: E.g., as a ugrad, I tried to be a physics major but too frequently got totally torqued off at the sloppy math so majored only in math.

To try to make a long story and explanation short, it appears that a common approach is just to go ahead and say "shown" and synonyms and keep saying that until there is some serious contradiction, conflict, new news, etc.

Still, "shown", ..., "absolutely confident" are not easy to achieve: It appears that we have a right to assume that such work did build on the accepted physics, got the arithmetic right, got the math right or close enough, etc.

And, there are some assumptions rarely explained: E.g., for these observations claimed to be from 13.5 billion years ago, we have to assume, maybe, things like the spectral lines of hydrogen, deuterium, etc. have not changed, the clock ticks and meter sticks mean the same as on Earth now, etc. Heck, maybe 13.5 billion years ago there was no hydrogen yet and dark matter radiated what we now believe came from hydrogen??? Here I'm making just wild stabs: A real conflict in the accepted results of physics would be big news and is not easy to find -- I can't give real examples here or at all.

So, for now, and until there is some big reason otherwise, we just let physics say "shown", ..., "absolutely confident". These are not nearly the worst ways the English language is sometimes used!

Triangulation doesn't especially add much (or, in fact anything at all) when the base of the triangle is 2 AU across (the diameter of the Earth's orbit, or roughly 16 light minutes) and the long axis of the triangle is 13.4 billion light years.

It's not color == distance though, it is color + brightness. Maybe there is some unknown principle at play but you could say that about anything which is not directly measurable, for example how old the earth is. But, it's the best we've got so far, and it does provide seemingly reasonable results that also align with parallax measurements when parallax is within the usable range.

"Colour" is oversimplifying it a bit. We're usually concerned with the distribution of light received with respect to wavelength. In the case of distance, it's not just that "it's red", but that the entire spectrum has been shifted in the direction of red. That means the features that correspond to, say, a specific Hydrogen emission, appear slightly offset from where they would if you were looking at it in a lab. When you look at age and size, you're looking at the distribution of the spectrum irrespective of a shift and seeing if it's heavier in the red, blue, or somewhere else. That tells you a lot about composition and mass, which helps with the age and size questions.

TL;DR: the use of color terms (e.g., "red") is oversimplifying what astronomers actually do which is an analysis of the overall spectrum and its properties.

For those wondering [1]

  GN-z11 is a high-redshift galaxy found in the constellation Ursa Major. It is one of the farthest known galaxies from Earth ever discovered

[1] https://en.wikipedia.org/wiki/GN-z11

That's just the size, to see it with the naked eye it'd need to be bright enough and in the right wavelength range but it is neither bright enough nor in a wavelength visible to the naked eye.

The article doesn't make it obvious but that's not the size of the galaxy, that's the size of the part of the sky they looked through. They make it sound like they looked through 100,000 galaxies in that sliver of sky and found the 2-4 older-than-anything-we've-seen-before galaxies.

I think this is perhaps the wrong way to think about it. 50 million years represents ~14% of the age of the Universe (at 350 Myr) so it's really quite a big jump. Considering stars aren't thought to form until 200-250 Myr after the Big Bang, we're talking 33%-50% closer to this period. That's quite remarkable considering the was well out of reach just a year ago.

I think it is too early to tell, however there may not have been enough stuff other than Hydrogen and Helium in the early universe to get terrestial planets.

Very large stars on the other hand don't live very long (just tens of millions of years) before they go Supernova and produce the elements that are heavier than iron.