APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Comments and questions about the APOD on the main view screen.
longtry
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by longtry » Wed Jul 17, 2019 10:36 am

I'm a bit confused here. By 'elliptical' did you mean the interacting spirals (IS)? Because in the picture, the most notable elliptical is the bright, dominant one very near the center of the dark matter, meanwhile the Einstein cross appears around the yellow core of 1 of 2 IS.

Assuming that you did mean IS, both Rob and I think the physical position of SN is nearly straight behind that IS. For me, because earlier in this very thread, there was an explanation about how Einstein cross can form, and how it must be 4 points not 3, 5, or a circle. That post (very convincing, with pictures and links from stackexchange) emphasized that the light source must be directly behind the center of the cross, just a wee bit off. Otherwise it can't happen at all.

One could hypothesize that the HC bent light from the SN so that when it came to the IS, it's straight behind from our perspective. That means light went SN => HC => IS => Earth. But earlier when I ask question no.1 about the order of things, Rob (again) told us that the IS is part of the HC and no one raised objections, so light went SN => (HC+IS) => Earth. That makes the hypothesis impossible.

Therefore, unless we have clear source from the scientist team stating where the SN is in the picture, my marked position is a way better guess than somewhere in the green circle.

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Chris Peterson
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by Chris Peterson » Wed Jul 17, 2019 12:54 pm

longtry wrote:
Wed Jul 17, 2019 10:36 am
Therefore, unless we have clear source from the scientist team stating where the SN is in the picture, my marked position is a way better guess than somewhere in the green circle.
Why? This is not a homogeneous lens. The light is taking multiple paths through the dark matter halo. The most reasonable location for the SN is near the center-of-mass of the entire halo. (More precisely, multiple lensed objects are identified in the field, which are used to define a mass profile and critical lines, which are roughly analogous to the shape of the lens.)
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longtry
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by longtry » Thu Jul 18, 2019 1:52 pm

I've explained the reason behind mentioned quote right in the previous post.

Regarding your picture, since you didn't provide more info with it, but it looks professional, I suppose that it's a publication by the scientist team behind the research. Note that they didn't pinpoint the SN real location, though.

Now, let's assume your theory of the SN position is behind or around the dominant elliptical (DE), which is at the center of the dark matter's critical line, too. There are problems with it. We can say assuredly that the 1.1 IS is nearer to that DM center than the 1.3 galaxy. If SN light ever come our way from those 2 locations, 1.1 must come 1st because light needs to bend less, and thus travel less, than 1.3. But the original picture says SN may have been in 1.3 in 1995. And we saw SN in 1.1 in 2014.

Aside from that, there's no debate at all that 1.2 is nearer to the lens center than both 1.1 & 1.3. How can light came from it latest of all, in 2015??

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Chris Peterson
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by Chris Peterson » Thu Jul 18, 2019 2:02 pm

longtry wrote:
Thu Jul 18, 2019 1:52 pm
Regarding your picture, since you didn't provide more info with it, but it looks professional, I suppose that it's a publication by the scientist team behind the research.
It's from the original paper, which is referenced in the APOD caption. I suggest you read it and understand how these lens models are made before simply guessing where you think the SN lies in the field. Because your guess is wrong... it's as simple as that.
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by longtry » Fri Jul 19, 2019 7:30 am

Thanks Chris, I've read the article. Some points from it:
1.
Your suggested paper wrote:Three images of the host galaxy formed by the cluster are marked with white labels (1.1, 1.2, and 1.3) in the left panel, and each is enlarged at right.
So the SN actually happened in the IS. Thus the 'correct' order is: IS having SN => HC => Earth.

2. What appears to be the bright core of the IS is actually another elliptical of the HC, that happens to be along the line to the IS when viewed from Earth.

3. The article never said the SN real position is behind the DE, i.e. where the center of dark matter is. So your guess can just be as good as mine. In fact, after reading the article & getting point 1 & 2 cleared as above, my guess turned out to be the correct one.