Starship Asterisk*

by **Chris Peterson** » Tue Apr 11, 2017 8:49 pm

BDanielMayfield wrote:
Chris Peterson wrote:Define "complete". The first science phase involves the initial 66 antennas. But I think there are plans to add more. Most large observatories are never really complete, there's just a date where they go into regular use.
Complete as in construction and installation of the initial design with the 66 large antennas is finished.

Sure. But from ALMA's standpoint, it may remain reasonable to call the facility "under construction" as long as they have plans for significant expansion. Or maybe they just haven't updated their site- there are other comments on that page that sound out-of-date.

by **BDanielMayfield** » Tue Apr 11, 2017 8:44 pm

Chris Peterson wrote:Define "complete". The first science phase involves the initial 66 antennas. But I think there are plans to add more. Most large observatories are never really complete, there's just a date where they go into regular use.

Complete as in construction and installation of the initial design with the 66 large antennas is finished.

by **Chris Peterson** » Tue Apr 11, 2017 8:37 pm

BDanielMayfield wrote:
DavidLeodis wrote:In the information (but undated) in the ALMA website that is brought up through the 'ALMA' link in the explanation http://www.almaobservatory.org/en/about-alma it states ALMA is "Currently under construction...". That surprised me so I looked up information elsewhere and in that in Wikipedia (https://en.wikipedia.org/wiki/Atacama_L ... eter_Array it states "The array has been fully operational since March 2013". Assuming that Wikipedia is correct I thought I would mention it in case anyone else thought it odd that ALMA was apparently still under construction.
I wondered if it might still be under construction in the sense of more radio dishes still being added, but that's not the case. It is complete, and has been since March 13, 2013.

Define "complete". The first science phase involves the initial 66 antennas. But I think there are plans to add more. Most large observatories are never really complete, there's just a date where they go into regular use.

by **BDanielMayfield** » Tue Apr 11, 2017 8:27 pm

DavidLeodis wrote:In the information (but undated) in the ALMA website that is brought up through the 'ALMA' link in the explanation http://www.almaobservatory.org/en/about-alma it states ALMA is "Currently under construction...". That surprised me so I looked up information elsewhere and in that in Wikipedia (https://en.wikipedia.org/wiki/Atacama_L ... eter_Array it states "The array has been fully operational since March 2013". Assuming that Wikipedia is correct I thought I would mention it in case anyone else thought it odd that ALMA was apparently still under construction.

I wondered if it might still be under construction in the sense of more radio dishes still being added, but that's not the case. It is complete, and has been since March 13, 2013.

Bruce

by **DavidLeodis** » Tue Apr 11, 2017 5:59 pm

In the information (but undated) in the ALMA website that is brought up through the 'ALMA' link in the explanation http://www.almaobservatory.org/en/about-alma it states ALMA is "Currently under construction...". That surprised me so I looked up information elsewhere and in that in Wikipedia (https://en.wikipedia.org/wiki/Atacama_L ... eter_Array it states "The array has been fully operational since March 2013". Assuming that Wikipedia is correct I thought I would mention it in case anyone else thought it odd that ALMA was apparently still under construction.

by **Chris Peterson** » Tue Apr 11, 2017 3:41 pm

Anthony wrote:I was wonder if someone could explain why the MWB light is not affected by gravity lensing. I would expect a condensed ring of microwave Radiation around the Cluster.

I think there are a couple of factors involved. First, look at the optical lensing that is apparent. What we have is one (or maybe more) bright, nearly point source background objects being lensed around the cluster. In the case of the CMB, we have only a diffuse background that is almost perfectly uniform. So any lensing is going to be extremely low contrast. Combine this with the much lower resolution of the CMB background measurement, both spatially and in terms of intensity, and I think that answers your question. (Note the fine optical resolution, at near the pixel scale of the image, compared with the huge blobs of CMB with only a little variation in intensity.)

by **Anthony** » Tue Apr 11, 2017 3:27 pm

I was wonder if someone could explain why the MWB light is not affected by gravity lensing. I would expect a condensed ring of microwave Radiation around the Cluster.
brgds
Anthony

by **neufer** » Mon Apr 10, 2017 8:50 pm

: [b][color=#0000FF]The dashed line represents the intensity of the cosmic microwave background with radio frequency. The solid line is the distortiong in the cosmic background intensity due to inverse-Compton scattering of photons through the gas presents in a cluster of galaxies. This is a schematic representation: the actual distortion is much smaller. (Credit: Carlstrom et al., Annual Reviews of Astronomy & Astrophysics vol 40, pg 643, 2002) [/color][/b]

BDanielMayfield wrote:
The up-scattering of photons was a new concept to me. I'm not questioning this process, but wouldn't the effect be the same if the CMB photons where merely deflected without altering their energies?

For every CMB photon deflected away from us there is a CMB photon deflected towards us (as in the cartoon above).

Blue shift is the only sure way to distinguish these features.

by **BDanielMayfield** » Mon Apr 10, 2017 7:08 pm

The up-scattering of photons was a new concept to me. I'm not questioning this process, but wouldn't the effect be the same if the CMB photons where merely deflected without altering their energies?

Bruce

by **sillyworm** » Mon Apr 10, 2017 6:22 pm

Thanks Chris You answered my question in your reply to CSW

by **Fred the Cat** » Mon Apr 10, 2017 6:20 pm

Wonder if the earliest clusters would have produced a sour note in our universe? Maybe just a hiccup.

by **neufer** » Mon Apr 10, 2017 6:16 pm

: [b][color=#0000FF]Schematic of the Sunyaev-Zeldovich effect that results in an increase in higher energy (blue shifted) photons of the CMR when seen through the hot gas present in cluster of galaxies. [size=85]http://astro.uchicago.edu/sza/primer.html (Adapted from L. Van Speybroeck)[/size][/color][/b]

Tszabeau wrote:
The discussion makes it seem a bit more like a shadow than a hole.

You could call it a shadow.

by **Tszabeau** » Mon Apr 10, 2017 5:18 pm

The discussion makes it seem a bit more like a shadow than a hole.
If it's a hole, is it cylindrical and we are within the "cylinder"?

by **Chris Peterson** » Mon Apr 10, 2017 4:38 pm

csw wrote:I've never understood how CMB can be "all around us" if it originated more or less from a single point, or at least a defined area. Shouldn't it be sort of like the sun's rays coming at us from only one direction -- from where the sun is? How can CMB bombard us from ALL angles?

It didn't originate at a single point- not even close to it. It originated nearly uniformly throughout the volume of an already expanded Universe. The entire Universe was at about 3000 K, so it was glowing in visible light. The photons that still exist have been traveling through expanding space, so they are now microwave photons. The edge of the observable universe represents regions of space that were nearly adjacent to us after the Big Bang.

by **sillyworm** » Mon Apr 10, 2017 4:36 pm

Thank you Bruce & Chris.I guess what I was thinking was..Why...since the CMB photons were sent prior(?) to the formation of these galaxies...we don't see a background image unaltered by the Galaxies? Because the CMB is receding the photons are actually taking longer to get here because of this expansion? Thanks so much!!!!!!

by **csw** » Mon Apr 10, 2017 4:24 pm

I've never understood how CMB can be "all around us" if it originated more or less from a single point, or at least a defined area. Shouldn't it be sort of like the sun's rays coming at us from only one direction -- from where the sun is? How can CMB bombard us from ALL angles?

If the answer pertains to general or special relativity, and space expanding, please don't bother trying to explain it. I won't get it.

Thanks!

Amateurishly,

Chris

by **Chris Peterson** » Mon Apr 10, 2017 2:46 pm

sillyworm wrote:I'm aware of the billions of year factor....I now see that the CMB is also a spectral light image(?) ...so..it appears to us NOW as it was at the beginning of the BIG BANG process?I'm pondering WHY the cluster(s) would be "punching" a hole in the CMB if the CMB came first? Or is the image of the CMB altered along with the changes that have occurred with all the Galaxies,etc?

The CMB represents photons that were released about 380,000 years after the Big Bang. They were produced by a 3000 K source, meaning that they peaked as yellow light (but having a wide spectral range). They've traveled for 13.7 billion years, during which time their point of origin has receded from us by some 46 billion light years. That expansion caused the photon wavelengths to be stretched out, from visible light to a few millimeter microwaves.

The clusters "punch holes" in the CMB in the sense that they alter its appearance by scattering CMB photons that pass through them.

by **sillyworm** » Mon Apr 10, 2017 2:33 pm

I'm aware of the billions of year factor....I now see that the CMB is also a spectral light image(?) ...so..it appears to us NOW as it was at the beginning of the BIG BANG process?I'm pondering WHY the cluster(s) would be "punching" a hole in the CMB if the CMB came first? Or is the image of the CMB altered along with the changes that have occurred with all the Galaxies,etc?

by **BDanielMayfield** » Mon Apr 10, 2017 2:07 pm

sillyworm wrote:When observing the Galaxy clusters we are seeing them as they appeared many years ago.When observing the CMB ...does it appear to us in REAL time?

Time is real in all epochs.

We're seeing the galactic clusters as they were billions of years ago, the CMB is even older, the edge of the observable universe.

Bruce

by **sillyworm** » Mon Apr 10, 2017 1:55 pm

When observing the Galaxy clusters we are seeing them as they appeared many years ago.When observing the CMB ...does it appear to us in REAL time?

by **BDanielMayfield** » Mon Apr 10, 2017 1:37 pm

neufer wrote:
BDanielMayfield wrote:
How do we know for sure (or, are we in fact sure) that something similar, but on a smaller scale to the SZ effect is not the cause of the more general fluctuations in the CMB?

Probably can't be entirely sure for the small scale CMB fluctuations.

https://en.wikipedia.org/wiki/Sunyaev%E2%80%93Zel%27dovich_effect wrote:
<<To distinguish the SZ effect due to galaxy clusters from ordinary density perturbations, both the spectral dependence and the spatial dependence of fluctuations in the cosmic microwave background are used. Analysis of CMB data at higher angular resolution (high l values) requires taking into account the Sunyaev–Zel'dovich effect.>>

Very nice answer Art. Thanks.

Bruce

by **neufer** » Mon Apr 10, 2017 1:01 pm

BDanielMayfield wrote:
Tszabeau wrote:
What would the hole look like if it was "uniform"?
The edges of the hole would be more round or elliptical.

Bruce

by **BDanielMayfield** » Mon Apr 10, 2017 12:57 pm

Tszabeau wrote:What would the hole look like if it was "uniform"?

The edges of the hole would be more round or elliptical.

Bruce

by **neufer** » Mon Apr 10, 2017 12:36 pm

BDanielMayfield wrote:
How do we know for sure (or, are we in fact sure) that something similar, but on a smaller scale to the SZ effect is not the cause of the more general fluctuations in the CMB?

Probably can't be entirely sure for the small scale CMB fluctuations.

https://en.wikipedia.org/wiki/Sunyaev%E2%80%93Zel%27dovich_effect wrote:
<<To distinguish the SZ effect due to galaxy clusters from ordinary density perturbations, both the spectral dependence and the spatial dependence of fluctuations in the cosmic microwave background are used. Analysis of CMB data at higher angular resolution (high l values) requires taking into account the Sunyaev–Zel'dovich effect.>>

by **Tszabeau** » Mon Apr 10, 2017 12:35 pm

What would the hole look like if it was "uniform"?

Starship Asterisk*

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