JWST distant galaxies

[gort]

According to the NASA website: "Light from these galaxies took billions of years to reach us. We are looking back in time to within a billion years after the big bang when viewing the youngest galaxies in this field. The light was stretched by the expansion of the universe to infrared wavelengths that Webb was designed to observe. "

So the most distant (youngest) galaxies are at 12.7 B ly away. If we can believe the value of Hubble's Constant (from the Chandra X-ray observatory), it's 77 km/s/megaparsec. At 12.7 B ly away, that gives a recession speed of about 300,000 km/s or about the speed of light. Now, even if Hubble's Constant is a bit wrong, we're looking at red shifts from visible not just to the near and mid infrared. If we see anything with the JWST at 12.7 B ly distant, we'd be seeing x-ray objects (supernovae, black hole accretions). I don't think the JWST would be seeing galaxies and "normal" stars at that distance, simply due to the huge redshift.

Is my math wrong? Is the reasoning wrong? Or is it just NASA hype and we'll never approach those distant views with JWST?

Cheers,

James

[robin_astro]

The "recession velocity"  depends on the observer (relativity) and the cosmological model so you can't really talk about a recession velocity. Using the currently accepted parameters for the universe, objects from 1 billion years after the big bang will show a cosmological redshift ~6.  You can use Ned Wrights cosmology calculator to play with these figures.

https://www.astro.ucla.edu/~wright/CosmoCalc.html

The Hydrogen Lyman alpha line, at 121.6 nm in the UV at rest is commonly used to measure objects at high redshifts. This will therefore be at 7x121.6 nm or 0.85um so at the short wavelength end of the  JWST spectrum (it is even in the passband of amateur CMOS/CCD detectors.)   Here for example are some of my spectra showing Lyman alpha of objects at 4.5 redshift, shifted in to the red regiom of the visible spectrum (~1.3 billion years after the big bang)

https://britastro.org/observations/observation.php?id=20210411_134753_85f4b3ebf4faaefe 

Cheers

Robin

Edited July 13, 2022 by robin_astro
typo

[robin_astro]

11 minutes ago, robin_astro said:

The Hydrogen Lyman alpha line, at 121.6 nm in the UV at rest is commonly used to measure objects at high redshifts. This will therefore be at 7x121.6 nm or 0.85um so at the short wavelength end of the  JWST spectrum

Extending this to more familiar wavelengths, at redshift 6 H alpha is at 7x656.3nm or 4.6um (JWST can see down to 28.3 um so theoretically  it could see H alpha at 42 redshift or 60 million years after the big bang !)

Robin

[robin_astro]

21 minutes ago, robin_astro said:

The "recession velocity"  depends on the observer (relativity) and the cosmological model so you can't really talk about a recession velocity.

If you want to dig further down this rabbit hole then you could visit  NED Wright's cosmology FAQ 

https://www.astro.ucla.edu/~wright/cosmology_faq.html

Cheers

Robin

[gort]

Thanks for the references, Robin. Makes sense now.

Cheers,

James

[Macavity]

Fascinating stuff re. "youngest" Galaxies (after the Big Bang!?!). 😎
Notably galaxies seem quite SMALL (compared to ours!)
Consist of "First Generation" (Hydrogen only) stars?
I forget... don't know... All GOOD STUFF! 🥳

Business Insider? Teasing/Musing! 😅

Edited July 21, 2022 by Macavity

[Alien 13]

12 hours ago, Macavity said:

Fascinating stuff re. "youngest" Galaxies (after the Big Bang!?!). 😎
Notably galaxies seem quite SMALL (compared to ours!)
Consist of "First Generation" (Hydrogen only) stars?
I forget... don't know... All GOOD STUFF! 🥳

Business Insider? Teasing/Musing! 😅

Have read that the first galaxies were only a few hundred million years or less after the big bang which  begs the question of which came first, stars or galaxies.

Alan

[Macavity]

11 hours ago, Alien 13 said:

Have read that the first galaxies were only a few hundred million years or less after the big bang which
  begs the question of which came first, stars or galaxies.

Heheh - But quite so! I think we all have notions of the "age of things"... Solar system
... Universe etc. Some of us (maybe) the life of 1st gen. stars... "Millions not Billions"?
The sun was "born in an Open Cluster". But, maybe, what constitutes a "galaxy" etc. 🤔

Recently, I was impressed by the (past / future) frequency of STARS wandering into
close proximity of our solar system! We live in interesting boring times (thankfully)? 😅
https://astronomy.com/news/2020/05/wandering-stars-brush-past-our-solar-system-surprisingly-often

Edited July 22, 2022 by Macavity