APOD: Galaxy Cluster Gas Creates Hole in... (2017 Apr 10)

Comments and questions about the APOD on the main view screen.
Anthony

Re: APOD: Galaxy Cluster Gas Creates Hole in... (2017 Apr 10)

Postby 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.
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Chris Peterson
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Re: APOD: Galaxy Cluster Gas Creates Hole in... (2017 Apr 10)

Postby 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.)
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Re: APOD: Galaxy Cluster Gas Creates Hole in... (2017 Apr 10)

Postby 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_Large_Millimeter_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.

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Re: APOD: Galaxy Cluster Gas Creates Hole in... (2017 Apr 10)

Postby 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_Large_Millimeter_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.

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Re: APOD: Galaxy Cluster Gas Creates Hole in... (2017 Apr 10)

Postby 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_Large_Millimeter_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.
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Re: APOD: Galaxy Cluster Gas Creates Hole in... (2017 Apr 10)

Postby 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.
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Re: APOD: Galaxy Cluster Gas Creates Hole in... (2017 Apr 10)

Postby 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.
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