Comments on: Galaxy Cluster Far, Far Away Smashes Distance Record

By: Dark Tzar

Dark Tzar — Wed, 28 Oct 2009 22:31:40 +0000

OK, this is something that confuses me, perhaps because I do not understand the underlying maths.
If something is 10 billion LY away from us today, then 10 billion years ago it must have been a lot closer (if we are to assume the expanding universe/big bang theory).
So, to see something that is now 10 billion LY away from us means that it is no longer there but a lot further away from us as we are seeing it where it was 10 billion years ago.
If the universe is (for all approximations and averages) about 15 billion years old, how can something be seen as being that far away, or even further if some of the other objects are used (13+ billion LY distant)?
If someone can explain this to me it will help me sleep at night.
And for the record, I feel that the explanation behind red shift is flawed. I feel it is a measure of distance, but not of how fast something is receding from us. But that is another argument.

By: Astrofiend

Astrofiend — Fri, 23 Oct 2009 05:36:06 +0000

Meh – I guess it's kind of far… I've seen further.

By: Homme du Sud

Homme du Sud — Fri, 23 Oct 2009 01:18:57 +0000

Boy, thats a long way…

By: Lawrence B. Crowell

Lawrence B. Crowell — Thu, 22 Oct 2009 23:49:53 +0000

The observed values of z are quoted as 1.91 in

http://arxiv.org/PS_cache/arxiv/pdf/0812/0812.1699v2.pdf .

The FLRW spacetime metric result on the Doppler shift is for R(T) = radius of cosmic region now, R(t) = radius of same region at previous time t is

z = R(T)/R(t) – 1

so R(t) =~ R(T)/2.9. If I assume a "coasting universe," or where the mutual gravitation of galaxies on average is small and the accelerated expansion of the universe is small enough that would give a similar ratio of times T/t =~ 2.9. That is about 4.7 billion years after the big bang. If I ignore frame dragging effects then that would be about 9 billion Ly away. So the numbers seem to match.

What appears to make these interesting is they are clusters of galaxies, so they represent the largest identified gravtiationally bound objects identified this early in the unvierse. There are some z = 7 objects which have been identified, which puts them out to 2 billion years after the BB.

By: Jon Hanford

Jon Hanford — Thu, 22 Oct 2009 22:25:51 +0000

Oh yeah, the paper on the discovery of JKCS 041 can be found here: http://arxiv.org/PS_cache/arxiv/pdf/0812/0812.1699v2.pdf .

By: Jon Hanford

Jon Hanford — Thu, 22 Oct 2009 22:22:14 +0000

I recently came across this paper on the arXiv site & was hoping UT would write it up. The article includes only a mediocre image of the cluster embedded in the blue X-ray glow. An awesome 3 color image obtained with the 3.6m CFHT is well worth a gander here: http://www.brera.mi.astro.it/~andreon/JKCS041_WIRDS_gzK_T0002.jpg . These really are some distant, red galaxies (see link). The paper mentions that a 12 hour spectrum across the cluster taken with one of the 8 meter VLT 'scopes detected NO galaxies, hence the redshift is derived photometrically. Detailed spectra and direct imaging of this cluster sounds like a perfect job for Hubble.

By: DrFlimmer

DrFlimmer — Thu, 22 Oct 2009 18:09:57 +0000

Once upon a time in a galaxy cluster very, very, very far away……

Couldn't resist