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

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

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

Post by AmazedAstronomer » Mon Mar 09, 2015 7:29 pm

Still amazes me how visible these events are and that one could very well wipe out a large portion of the galaxy.

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

Post by Chris Peterson » Mon Mar 09, 2015 8:08 pm

AmazedAstronomer wrote:Still amazes me how visible these events are and that one could very well wipe out a large portion of the galaxy.
Not really. Supernovas like these have no destructive effect on even nearby stars or planets, and are only potentially harmful to life for a distance of around 100 light years. That represents an insignificant fraction of any galaxy.
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by neufer » Mon Mar 09, 2015 8:25 pm

Ron-Astro Pharmacist wrote:The configuration of supernovae points almost seems similar to the points from which gravitational lensing has been studied.

http://arxiv.org/ftp/arxiv/papers/0806/0806.1884.pdf

If the dynamic system remained still keeping it free from distortion could the fifth point fall upon the L2 position?

http://en.wikipedia.org/wiki/Lagrangian_point
Similarity with the 5 orbital Lagrange points is purely coincidental.

If the gravitational lens body is sufficiently spread out it will form a fifth (maximum travel time path) point close to the the center of symmetry of the gravitational lens galaxy.

The good news in the case of today's APOD is that this fifth point will be the very last to show the supernova peak intensity.

The bad news, of course, is that it will be hidden by the gravitational lens galaxy itself.
neufer wrote:
Pierre de Fermat in 1662 stated that a light ray travels from point P to point P',
along a path which takes the least time(; e.g., an Einstein ring).

In actuality, light ray travel from point P to point P', along a path
for which the travel time is either minimum, maximum or a saddle point.

The four Fermat travel paths of an off center gravitational lens Einstein cross represent:
[list]1) two minimum travel time paths and
2) two saddle point travel time paths:[/list]
Art Neuendorffer

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

Post by Ron-Astro Pharmacist » Mon Mar 09, 2015 9:35 pm

neufer wrote:
Ron-Astro Pharmacist wrote:The configuration of supernovae points almost seems similar to the points from which gravitational lensing has been studied.

http://arxiv.org/ftp/arxiv/papers/0806/0806.1884.pdf

If the dynamic system remained still keeping it free from distortion could the fifth point fall upon the L2 position?

http://en.wikipedia.org/wiki/Lagrangian_point
Similarity with the 5 orbital Lagrange points is purely coincidental.

If the gravitational lens body is sufficiently spread out it will form a fifth (maximum travel time path) point close to the the center of symmetry of the gravitational lens galaxy.

The good news in the case of today's APOD is that this fifth point will be the very last to show the supernova peak intensity.

The bad news, of course, is that it will be hidden by the gravitational lens galaxy itself.
neufer wrote:
Pierre de Fermat in 1662 stated that a light ray travels from point P to point P',
along a path which takes the least time(; e.g., an Einstein ring).

In actuality, light ray travel from point P to point P', along a path
for which the travel time is either minimum, maximum or a saddle point.

The four Fermat travel paths of an off center gravitational lens Einstein cross represent:
[list]1) two minimum travel time paths and
2) two saddle point travel time paths:[/list]
Thanks Art. I know little about the curious (to me) effect of Lagrange points so I was curious if it could work on the large scale as it does on the smaller scale of our sun and planets.
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by geckzilla » Mon Mar 09, 2015 10:14 pm

R. H. MacDonald wrote:
geckzilla wrote: I have the same problem understanding how it happens. Rings are formed by spherical masses and crosses by flattened ones. I'm not sure how it works, though. But it is not hard to believe that it happens especially seeing all of the examples Hubble has provided us with. I just have to accept that I don't understand it well enough for it to be intuitive.
Thank you for your reply. Questions and answers are great ways to come up with more questions and answers. :)

I just have to accept that I don't understand it well enough for it to be intuitive.

The most read book in the history of mankind has that caveat to its basis. You just have to accept things by faith and faith alone.

I do not. If the chair looks to me like I can sit in it, I'll take the risk. If there is a leg missing, I won't. So, I study chairs in my own limited, uneducated way.
Well, I'm a little insulted that you've equated my take on things to faith. It's more about knowledge in progress than faith. I don't accept that I will and can never understand something. It's just that right now, at this moment, I don't. It's an acceptance of ignorance. That's the complete opposite of faith.
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by Chris Peterson » Mon Mar 09, 2015 10:20 pm

geckzilla wrote:Well, I'm a little insulted that you've equated my take on things to faith. It's more about knowledge in progress than faith. I don't accept that I will and can never understand something. It's just that right now, at this moment, I don't. It's an acceptance of ignorance. That's the complete opposite of faith.
Also, you aren't suggesting the phenomenon isn't real. You can observe it yourself, and you quite reasonably trust the view of experts that it can be explained by GR, even if you yourself can't easily make or follow that explanation (certainly not enough to have an intuitive feel at this point). Believing people who know a lot about some subject isn't something that should be called "faith".
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by Nitpicker » Tue Mar 10, 2015 12:13 am

The different patterns resulting from gravitational lensing, seem analogous to the different kinds of diffraction patterns one gets with different obstructions inside a telescope.

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

Post by Chris Peterson » Tue Mar 10, 2015 12:37 am

Nitpicker wrote:The different patterns resulting from gravitational lensing, seem analogous to the different kinds of diffraction patterns one gets with different obstructions inside a telescope.
They aren't, though. Gravitational lensing isn't a diffractive process at all. It isn't refractive, either, although it is analogous to refraction in many ways.

Gravitational lenses can't produce real images, because unlike a normal refractive lens, their power is highest in the center and falls off with distance. Imaging lenses are zero power through their centers, and increase in power as the radial distance increases.
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by Nitpicker » Tue Mar 10, 2015 1:48 am

Chris Peterson wrote:
Nitpicker wrote:The different patterns resulting from gravitational lensing, seem analogous to the different kinds of diffraction patterns one gets with different obstructions inside a telescope.
They aren't, though. Gravitational lensing isn't a diffractive process at all. It isn't refractive, either, although it is analogous to refraction in many ways.

Gravitational lenses can't produce real images, because unlike a normal refractive lens, their power is highest in the center and falls off with distance. Imaging lenses are zero power through their centers, and increase in power as the radial distance increases.
Gravitational lensing patterns do not have to result from diffraction, in order to be analogous to the diffraction patterns observed through different telescope designs. The differing shapes of the gravitational fields (surrounding the galaxy clusters) which form the gravitational lens, are analogous to the differing shapes of the telescope obstructions. Was meant as a geometric analogy only, as neufer's contour map of inverse brightness, was reminiscent of a diffraction pattern, at least in appearance.

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

Post by alter-ego » Tue Mar 10, 2015 4:13 am

Dad is watching wrote: We see four images and expect one more, but is this number limited? If the lensing is a result of a non-symetrical collection of masses, could we not discover a situation where the number of 'lensed images' could be 8 or 10 or more in dependence on the complexity of the non-symmetrical lens?
Because the host galaxy is itself lensed to show up in multiple positions, there are likely more than 5 supernova appearances. The picture shows 3 host galaxy locations and a total of 6 supernova appearances, one past, 4 present, and 1 future. To clarify, the possible past and future appearance occur in other host galaxy images.
Hubble Sees Supernova Split .JPG
http://hubblesite.org/newscenter/archiv ... 8/image/e/
Also, in today's image where we see the four 'maxima', if the exposure was longer in duration, would we see some sort of connecting image filament forming between the four maxima? Not circular, of course because the lens material is not symetrical, but more snake-like?
I don't believe so. The stellar appearance is a distinct solution for the cross as indicated in the toroidal surface in Art's post, i.e. the two maxima and two saddle positions. The arc / snake-like structures are other lensing solutions.
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by Chris Peterson » Tue Mar 10, 2015 4:32 am

Nitpicker wrote:Gravitational lensing patterns do not have to result from diffraction, in order to be analogous to the diffraction patterns observed through different telescope designs. The differing shapes of the gravitational fields (surrounding the galaxy clusters) which form the gravitational lens, are analogous to the differing shapes of the telescope obstructions. Was meant as a geometric analogy only, as neufer's contour map of inverse brightness, was reminiscent of a diffraction pattern, at least in appearance.
To make that geometrical analogy when we're talking about another- and completely unrelated- optical phenomenon is very confusing. I'd certainly avoid it. If you're talking about a geometrical similarity, call it a geometrical similarity. But the wording you chose certainly suggests a phenomenological relationship between the two, even if you didn't mean it that way. As a picker of nits, you ought to appreciate the distinction!
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by Nitpicker » Tue Mar 10, 2015 6:22 am

Chris Peterson wrote:
Nitpicker wrote:Gravitational lensing patterns do not have to result from diffraction, in order to be analogous to the diffraction patterns observed through different telescope designs. The differing shapes of the gravitational fields (surrounding the galaxy clusters) which form the gravitational lens, are analogous to the differing shapes of the telescope obstructions. Was meant as a geometric analogy only, as neufer's contour map of inverse brightness, was reminiscent of a diffraction pattern, at least in appearance.
To make that geometrical analogy when we're talking about another- and completely unrelated- optical phenomenon is very confusing. I'd certainly avoid it. If you're talking about a geometrical similarity, call it a geometrical similarity. But the wording you chose certainly suggests a phenomenological relationship between the two, even if you didn't mean it that way. As a picker of nits, you ought to appreciate the distinction!
If you go back, you'll see that my analogy was initially stated as relating the resulting patterns. That implies a geometric analogy (which I made because I thought it was interesting, more than instructional). If I had intended to imply that gravitational lensing was a kind of diffraction, I think it would have been wrong to call it an analogy. But I'll concede that I didn't initially consider the possibility of my analogy being confusing in that way and I accept that I confused you.

Personally, I find the concept of mass bending light quite simple. What makes this particular gravitational lensing more difficult to grasp, is that it has a very particular geometry.

James Rhoades

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

Post by James Rhoades » Tue Mar 10, 2015 9:08 pm

At about four finger widths from the highlighted galaxy to the lower left corner is an object when viewed under magnification has a series of red objects arranged in a ring around the central object.

Is this another example of gravitational lens magnification.

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

Post by geckzilla » Tue Mar 10, 2015 9:59 pm

James Rhoades wrote:At about four finger widths from the highlighted galaxy to the lower left corner is an object when viewed under magnification has a series of red objects arranged in a ring around the central object.

Is this another example of gravitational lens magnification.
That's a point source and the dots are part of the telescope's point spread function at near-infrared wavelengths. It's probably a dim little Milky way star.
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by EchoDelta58 » Fri Mar 13, 2015 4:32 am

Why do four images appear? Why not two, or six, or etc.? Why doesn't the lens produce a ring?

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

Post by longtry » Sun Jul 14, 2019 8:20 am

Wow... the picture from Hubble site is amazing, and it raises many questions in my head that I can't possibly wrap them around without being able to understand each of them step by step. So, here they go:
1. In the picture, the 4 arrows point to 4 bright yellow points that appear inside a blue-y swirl in the south-southwest portion of an overwhelmingly big and fuzzy light source. As I understand it, the 4 bright points are identified as 1 supernova (SN); the blue swirl is actually 2 interacting spirals (IS) with distinct cores, like in the Antennae pair; and the big fuzzy thing is the dominant center of a huge cluster (HC) with many galaxies swimming all around the picture. Please correct me if I'm wrong.
Now the question is: what is the order of things? Is the SN inside the IS? Or is the IS inside the HC? Or did the SN happen in an even farther galaxy, so its light came to us through this sequence: SN => IS => HC => Earth?

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

Post by rstevenson » Sun Jul 14, 2019 6:45 pm

longtry wrote:
Sun Jul 14, 2019 8:20 am
... Now the question is: what is the order of things? Is the SN inside the IS? Or is the IS inside the HC? Or did the SN happen in an even farther galaxy, so its light came to us through this sequence: SN => IS => HC => Earth?
As the description says:
The yellow-hued quadruply-imaged Supernova ... occurred in the early universe far behind the cluster.
So it's kind of SN => (IS + HC) => Earth.

Rob

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

Post by longtry » Mon Jul 15, 2019 3:54 am

dark matter centre.jpg
rstevenson wrote:
Sun Jul 14, 2019 6:45 pm
As the description says:
The yellow-hued quadruply-imaged Supernova ... occurred in the early universe far behind the cluster.
So it's kind of SN => (IS + HC) => Earth.
Thanks, Rob. If that's the case, then can you show me the place of the SN in the picture as if the IS+HC were not there at all?
Also, I've done a modified image myself to demonstrate what I think is the centre of the dark matter, based on the arcs of galaxies around. Please tell me what you guys think of its accuracy.
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by rstevenson » Mon Jul 15, 2019 12:51 pm

longtry wrote:
Mon Jul 15, 2019 3:54 am
dark matter centre.jpg
rstevenson wrote:
Sun Jul 14, 2019 6:45 pm
As the description says:
The yellow-hued quadruply-imaged Supernova ... occurred in the early universe far behind the cluster.
So it's kind of SN => (IS + HC) => Earth.
Thanks, Rob. If that's the case, then can you show me the place of the SN in the picture as if the IS+HC were not there at all? ...
Given the four almost equally spaced images of the SN around the bright blob, I would guess that the SN is directly behind it -- perhaps a little off center. But those in the know can likely calculate this instead of guess, and I'm just an interested amateur. For example, the center of mass of the entire cluster would also have an influence on the path the SN's light took getting to and around that blob.

Rob

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

Post by Chris Peterson » Mon Jul 15, 2019 1:08 pm

longtry wrote:
Sun Jul 14, 2019 8:20 am
Wow... the picture from Hubble site is amazing, and it raises many questions in my head that I can't possibly wrap them around without being able to understand each of them step by step. So, here they go:
1. In the picture, the 4 arrows point to 4 bright yellow points that appear inside a blue-y swirl in the south-southwest portion of an overwhelmingly big and fuzzy light source. As I understand it, the 4 bright points are identified as 1 supernova (SN); the blue swirl is actually 2 interacting spirals (IS) with distinct cores, like in the Antennae pair; and the big fuzzy thing is the dominant center of a huge cluster (HC) with many galaxies swimming all around the picture. Please correct me if I'm wrong.
Now the question is: what is the order of things? Is the SN inside the IS? Or is the IS inside the HC? Or did the SN happen in an even farther galaxy, so its light came to us through this sequence: SN => IS => HC => Earth?
All lensed objects that we observe involve a moderately distant large mass which deflects the light of a much more distant source. In this case, the lensing mass is the concentration of dark matter surrounding the visible galactic cluster, and the supernova that is lensed is very far behind that. Specifically, the lensing mass has z=0.54 (~5 Gly), and the SN has z=1.49 (~9 Gly). The distances derived from the redshifts are approximate, since "distance" has multiple interpretations with such high redshift values.
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by neufer » Mon Jul 15, 2019 4:26 pm

APOD Robot wrote:
Mon Mar 09, 2015 4:08 am
Image Galaxy and Cluster Create Four Images of Distant Supernova

Explanation: With patience and luck, a fifth image of the supernova will also be recovered nearby in the next few years.
With patience and [bad] luck, those two specific links have disappeared since "2015 Mar 09."

However, a fifth image of the supernova Sjur did appear nearby months later :!:
https://en.wikipedia.org/wiki/SN_Refsdal wrote:
<<SN Refsdal is the first detected multiply-lensed supernova, visible within the field of the galaxy cluster MACS J1149+2223. It was given its nickname in honor of the Norwegian astrophysicist Sjur Refsdal, who, in 1964, first proposed using time-delayed images from a lensed supernova to study the expansion of the universe. The host galaxy of SN Refsdal is at a redshift of 1.49, corresponding to a comoving distance of 14.4 billion light-years and a lookback time of 9.34 billion years. The multiple images are arranged around the elliptical galaxy at z = 0.54 in a cross-shaped pattern, also known as an "Einstein cross".

:arrow: The image to the left shows a part of the deep field observation of the galaxy cluster MACS J1149.5+2223 from the Frontier Fields programme. The circle indicates the predicted position of the newest appearance of the supernova. To the lower right the Einstein cross event from late 2014 is visible. The image on the top right shows observations by Hubble from October 2015, taken at the beginning of the observation programme to detect the newest appearance of the supernova. The image on the lower right shows the discovery of the Refsdal Supernova on 11 December 2015, as predicted by several different models.

After the discovery of the Refsdal Supernova, astronomers predicted that they would have the rare opportunity to see the supernova again in about one year, after the four images had faded away. This is because the initially observed four-image pattern was only one component of the lensing display. The supernova may have appeared as a single image some 40–50 years ago elsewhere in the cluster field.

The supernova Refsdal reappeared punctually at the predicted position between mid November 2015 and December 11, 2015 (with the exact date being uncertain by approximately one month which is the interval between two consecutive Hubble observations), in excellent agreement with the blind model predictions made before the reappearance was observed. The time delay between the original quadruplet observed in 2014 and the latest appearance of the supernova in 2015 was used to infer the value of the Hubble constant. This is the first time this technique, originally suggested by Refsdal, has been applied to supernovae.>>
Art Neuendorffer

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

Post by bystander » Mon Jul 15, 2019 4:59 pm

Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by longtry » Tue Jul 16, 2019 4:12 am

@bystander: thanks for the links... Actually, there are so many links I got lost. But all (most?) of them are articles with the purpose of spreading news to the target audience of average Johns. I'd love a link where we can see in a model (preferably 3D) what the shape and size of that HC's dark matter is, and the position of the SN too. After all, if the scientist team who made the announcement can predict the time of SN's reappearance with so much accuracy, surely they must have built a full model and know where things are?
Chris Peterson wrote:
Mon Jul 15, 2019 1:08 pm
Specifically, the lensing mass has z=0.54 (~5 Gly), and the SN has z=1.49 (~9 Gly).
I have a feeling that in order for Einstein stuffs (ring, cross) to appear, the distance to the lense need to be around half the distance to the source, otherwise lights can't focus on Earth. If that's true, then maybe the farthest lense we can have is about 8Gly away?
neufer wrote:
Mon Jul 15, 2019 4:26 pm
With patience and [bad] luck, those two specific links have disappeared since "2015 Mar 09."
Sometimes latecomers like me get a bit jealous of early birds.
rstevenson wrote:
Mon Jul 15, 2019 12:51 pm
Given the four almost equally spaced images of the SN around the bright blob, I would guess that the SN is directly behind it -- perhaps a little off center. But those in the know can likely calculate this instead of guess, and I'm just an interested amateur. For example, the center of mass of the entire cluster would also have an influence on the path the SN's light took getting to and around that blob.
Thanks again, Bob :) That's my guess too. It'd be much better if those guys in the know release more details of their research.

Since no one has commented on the previous pic, I suppose that everyone is OK with my assumption. Now with Bob's confirmation about the SN, I've modified the image once again, this time adding 2 red marks indicating the SN, 9Gly from Earth, in the position it would be in if there were no HC+IS at all. OK, time for 2nd question:
2. How could another ghost image of the SN "may" appear in the blue circle in 1995?? Light had to bend all the way around and thus needed to travel way way farther than through the nearly straight IS route. It'd be more like 2035 with the configuration we're talking about.
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Re: APOD: Galaxy and Cluster Create Four of... (2015 Mar 09)

Post by Chris Peterson » Tue Jul 16, 2019 4:35 am

longtry wrote:
Tue Jul 16, 2019 4:12 am
Since no one has commented on the previous pic, I suppose that everyone is OK with my assumption. Now with Bob's confirmation about the SN, I've modified the image once again, this time adding 2 red marks indicating the SN, 9Gly from Earth, in the position it would be in if there were no HC+IS at all. OK, time for 2nd question:
2. How could another ghost image of the SN "may" appear in the blue circle in 1995?? Light had to bend all the way around and thus needed to travel way way farther than through the nearly straight IS route. It'd be more like 2035 with the configuration we're talking about.
Why do you think the physical position of the SN is behind that elliptical galaxy? The primary lensing material here isn't any of these galaxies, but the vast dark matter halo that the galaxy cluster is embedded in. The light from the SN is taking multiple paths through that lens, reaching us at different times and in different apparent locations. The Einstein Cross around the elliptical simply shows a further splitting of one of those paths. Computer models have worked out the likely position of the actual SN in this field; there's no way we can do so simply by examining the image, however. (But it's probably fairly close to the identified mass center of the dark matter.)
Chris

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