Comments on: Mass of Hydrogen in Distant Galaxies Measured by Upgraded Giant Metrewave Radio Telescope

By: xABBAAA

xABBAAA — Sat, 17 Oct 2020 14:36:26 +0000

… when one thinks the outside of the Universe must be cold, and since the big inflation or bang, which way one prefers, the Universe is bit hotter than that outer layer of surrounding space. Moreover, the stuff tends to move from hot toward the cold.
Would that also contribute to faster spread of the Universe… Just wonder!…

By: Torbjörn Larsson

Torbjörn Larsson — Fri, 16 Oct 2020 19:22:29 +0000

Or I could have looked at the abstract where it is stated, silly me.

It also strikes me that apart from the redshift as such the peak will also broaden with the shift, so that may be what they really had problems with. [The paper is pay walled.]

By: Torbjörn Larsson

Torbjörn Larsson — Fri, 16 Oct 2020 19:13:52 +0000

Good catch! Yes, there seems to be a superfluous comma.

But a distance of 22 billion light years do not mean we are looking at galaxies that formed 22 billion years ago. The universe expansion isn’t linear. (And in fact dependent on the dominating energy type at a given time – inflation field, hot big bang radiation, matter, and recently vacuum (dark) energy – having a rapid exponential, hyperparabolic, parabolic, respectively slow exponential form. C.f. “Scale factor (cosmology)” @ Wikipedia.)

The observable universe is 14 billion years old but 92 billion light years across [c.f. “Observable universe” @ Wikipedia]. As the article say, galaxies that sits at 8 billion years of age out are at a redshift of ~1*, or at a luminosity distance of ~ 22108.66 Mlyr [search for a decent redshift calculator]. Incidentally, the 21 cm peak would lie at ~ 40 cm, which may be what the article describe as “the narrow bandwidth before the GMRT upgrade” that prohibited a larger sample.

* They really, really should always give the redshift in the article – I discovered that my favorite redshift calculator site was down and had to iterate the redshift on a more basic one. 🙁

By: Louie

Louie — Fri, 16 Oct 2020 14:53:43 +0000

Need to check some numbers. The legend in the picture shows “2,00,000” light years. I assume that should be 200,000 since most galaxies are not 2,000,000 light years in diameter. The caption states that the galaxy is 22B light years away. That pre-dates the big bang by about 6B years, according to current theory.