A Space & astronomy forum. SpaceBanter.com

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Research
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

The sea of galaxies and a big question

Thread Tools Display Modes
Old February 25th 21, 08:19 AM posted to sci.astro.research
jacob navia
external usenet poster
Posts: 341
Default The sea of galaxies and a big question

I have posted several times here about a "sea" of galaxies just beyond
the limit of our telescopes.

Two new obsevations start confirming the existence of this "sea".




.... It boggles the mind that over 90 percent of the galaxies in the
universe have yet to be studied. Who knows what interesting properties
we will find when we discover these galaxies with future generations of

The second obsevation is:



New Horizons Spacecraft Answers Question: How Dark Is Space?

The New horizons spacecraft, enjoying a sky 10 times darker than Hubble
has measured the background light of the Universe, i.e. the light from
space beyond ours and all other known galaxies.

I quote from the press release:

"... there may be many more faint, distant galaxies than theories
suggest. This would mean that the smooth distribution of galaxy sizes
measured to date rises steeply just beyond the faintest systems we can
see -- just as there are many more pebbles on a beach than rocks..."

Reference paper is:
arXiv:2011.03052v2 [astro-ph.GA] 9 Nov 2020

Now to my BIG question :-)

What is the difference between the cosmic background measured by the New
Horizons spacecraft and the CMB?

I know, one is in the micro-wave and the other is in visible. OK.

But couldn't the CMB be the same thing, i.e. the scattered, red-shifted
light of all the billions of galaxies that are just beyond the reach of
our telescopes?

If we assume that the Universe goes on forever, within a given solid
angle we should find more and more galaxies until all the field of view
is blocked by them. Since the red-shift decreases the energy of the
emitted light, the more distant galaxies just disappear completely,
red-shifted out of existence (for us). So there would have to be a
cutoff somewhere. And as we approach that limit, the galaxies lose their
individuality and become just a continuum of red-shifted light: the CMB

Why I am wrong?

Thanks in advance.


[[Mod. note -- It seems to me that there are three difficulties with
trying to explain the CMB as the scattered and red-shifted light of many
faint galaxies:
1. Individual galaxy spectra are non-black-body -- they have absorbtion
features from gas & dust within the galaxy, and from the stellar spectra
of the stars comprising the galaxies. If we add a bunch of such
non-black-body spectra, each with its own different (individual)
redshift, we'll get *some* composite spectrum. But it's highly
unlikely that all the non-black-body spectral features would cancel
out to 99.999% everywhere in the composite spectrum to yield a pure
single-temperature black-body spectrum, which is what the CMB looks
like (to about 1 part in 100,000).
2. That last 1-part-in-100,000 of the CMB varies over the sky in a very
specific way ("multipole decomposition"), and I can think of no reason
the superposition of many redshifted galaxy spectra would reproduce
that variation.
3. To red-shift a galaxy spectrum (color temperature of maybe 5000 K)
to a temperature 2.73 K would take a redshift of about 2500, corresponding
to a time of only about 5 million years after the big bang. That's
nowhere near enough time to form all these galaxies.
-- jt]]

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Newbie question - Viewing galaxies ag73 UK Astronomy 5 August 3rd 05 11:53 AM
question about the red shift and the velosity of the galaxies andreas UK Astronomy 2 September 25th 04 05:01 PM
Old Galaxies in the Young Universe: VLT Unravels New Population of Very Old Massive Galaxies (Forwarded) greywolf42 Astronomy Misc 6 August 11th 04 05:41 PM
Question on Gravity/black holes/galaxies. XeNO Misc 1 April 11th 04 09:34 PM
Faintest Spectra Ever Raise Glaring Question: Why do Galaxies inthe Young Universe Appear so Mature? (Forwarded) Andrew Yee Astronomy Misc 0 January 5th 04 07:39 PM

All times are GMT +1. The time now is 07:00 AM.

Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.
Copyright 2004-2022 SpaceBanter.com.
The comments are property of their posters.