Starship Asterisk*

Pandora's Cluster of Galaxies

Explanation: This deep field mosaicked image presents a stunning view of galaxy cluster Abell 2744 recorded by the James Webb Space Telescope's NIRCam. Also dubbed Pandora's Cluster, Abell 2744 itself appears to be a ponderous merger of three different massive galaxy clusters. It lies some 3.5 billion light-years away, toward the constellation Sculptor. Dominated by dark matter, the mega-cluster warps and distorts the fabric of spacetime, gravitationally lensing even more distant objects. Redder than the Pandora cluster galaxies many of the lensed sources are very distant galaxies in the early Universe, their lensed images stretched and distorted into arcs. Of course distinctive diffraction spikes mark foreground Milky Way stars. At the Pandora Cluster's estimated distance this cosmic box spans about 6 million light-years. But don't panic. You can explore the tantalizing region in a 2 minute video tour.

<< Previous APOD

This Day in APOD

Next APOD >>

I've always been amazed by science and capabilities of the instruments we have.

In such photo, apart from obvious spikey stars in our own galaxy, when every single object scene is a galaxy, at the distance of 3.5 bly and beyond, the instruments we have (and skills of algorithms and software) and the people we have can figure out each and every galaxy separately, along with their respective distances, which ones are really there vs which ones are gravitationally lensed (and how many copies), what's their age, what's their shape, what's their rotational direction, what elements are possibly in there (spectrum emitted by light by them), their speed of moving away (red shift).. ALL so precisely ?

I wonder if it's really possible to know to that extent OR maybe we just (incorrectly) think we know and can differentiate ? I mean, is there a chance of false confidence and complacency and case of "we don't even know that we don't know" ?

Today’s post is an exact duplicate of the one from Jun 09, 2023.

There is a Hubble image of a portion of Pandora's Cluster, and I decided to compare it with the same part of the cluster as imaged by Webb.


These are the objects I have annotated:

1) A disturbed very blue spiral galaxy. It doesn't look blue in the Webb image.

2) A pair of merging blue-white galaxies. There is a red object immediately below them that isn't visible in the Hubble image.

3) A deep red distant object. It is not seen by Hubble.

4) A compact blue-white galaxy.

5) Some elongated galactic fluff. It looks blue and very faint in the Hubble image, but red and more visible in the Webb image.

6) An elongated edge-on background galaxy. It is faint and barely red in the Hubble image, but redder and brighter in the picture by Webb.

7) A yellow non-starforming ring galaxy.

8) A red background spiral galaxy, redder and brighter but rather less detailed in the Webb image than in the Hubble picture.

9) A spiral galaxy with blue arms, more detailed in the Hubble image than in the picture by Webb.

10) Thin jets emerging from a massive elliptical galaxy. The jets look blue in the Hubble image and red in the Webb picture.

11) An elongated object that looks faint and blue by Hubble but red and reasonably bright by Webb.

12) A starforming spiral galaxy with blue clusters. The blue clusters become invisible n the Webb image.

13) A background galaxy that looks blue by Hubble and red by Webb.

14) Two overlapping galaxies, one orange and one blue. The blue galaxy looks red in the picture by Webb.

15) An arc made up of cyan-colored, yellow and blue objects. In the Webb image, all the objects are colorless and white.

16) A deep red object that is barely visible in the Hubble image.


In the Webb image, very distant objects apparently always look red, which helps us judge the relative distance to them. Dusty objects look red or somewhat red. Blue objects don't look blue and sometimes don't show details very clearly. Massive elliptical galaxies are surrounded by large halos in the Webb image. More objects can be seen in the Webb image than in the Hubble image.

Ann

Ann,
You're the "Colour Queen"! Surely all (or almost all) colours in astronomical photos are artificial, chosen at random when the wavelengths shown are beyond visible light or else exaggerated when they are so faint? That 'blue' galaxy is surely so by choice of the picture editor?

APoD,
Thank you for the link to the NASA video about the picture, which mentions the Red Dot (last 25 seconds) whose nature is unknown. In showing the Dot, the camera zoomed into the image, revealing multiple faint dots all over the dark sky between the stars and galaxies. They seemed to be white so not even more distance objects than the many red-shifted galaxies. What are these? Artefacts?

John

This image is simply GLORIOUS!
(The first link mentions it contains 50 000 "sources" - does that roughly mean 50 000 galaxies?)

shaileshs wrote: ↑Sat Jun 08, 2024 4:53 am I've always been amazed by science and capabilities of the instruments we have.

In such photo, apart from obvious spikey stars in our own galaxy, when every single object scene is a galaxy, at the distance of 3.5 bly and beyond, the instruments we have (and skills of algorithms and software) and the people we have can figure out each and every galaxy separately, along with their respective distances, which ones are really there vs which ones are gravitationally lensed (and how many copies), what's their age, what's their shape, what's their rotational direction, what elements are possibly in there (spectrum emitted by light by them), their speed of moving away (red shift).. ALL so precisely ?

I wonder if it's really possible to know to that extent OR maybe we just (incorrectly) think we know and can differentiate ? I mean, is there a chance of false confidence and complacency and case of "we don't even know that we don't know" ?

Well, "people" aren't figuring these things out, machines are. Subject to a generally pretty simple set of rules. In this many galaxies, there will be misidentifications. All measurements have error bars. But probably most of the identifications are accurate.

I was thinking what Ann has labeled object 8 is a dusty galaxy, and I thought I saw several dusty looking galaxies while zoomed into this image... but this is NIRCam, and when it takes pictures around the local milky way, it makes dust look transparent. So is this light really so distant that it used to be in the visible spectrum, and bounced off the dust like it does in the visible, but now from the red-shift it is in the near infrared?

Then I did a little more reading and found that answering questions about the dustiness is a major goal of the observing campaign, their UNCOVER research website is pretty nice.

"Though dusty star-formation dominates the SFR density below z~2, dust is not expected to play a large role at earlier times. However, dusty star formation is not well constrained at z>3. UNCOVER will detect any obscured galaxy with mass >109 M☉ out to z=9, if they exist, and can spectroscopically confirm this population to 28 AB mag."

The warping of spacetime in this image can be seen not only in the many lensed galaxies, but also broadly in the image as a whole when looked at from a certain distance: Instead of seeing galaxies "travelling" towards the center, for fun you can imagine the black space as a sheet behind which some giant invisible hand is slowly closing and squeezing everything, and all the galaxies follow. Of course their combined mass is that hand itself.
(you can also visualize the process in reverse, stretch out the wrinkled sheet and even out all the galaxies)

Ann wrote: ↑Sat Jun 08, 2024 6:03 am There is a Hubble image of a portion of Pandora's Cluster, and I decided to compare it with the same part of the cluster as imaged by Webb.

And to the ~4:30 position of Description #2, there is a quite blue little cluster that is red in Webb. There are lots of tiny blue dots that are red in Webb; such a big difference. Why?

zendae wrote: ↑Sat Jun 08, 2024 3:09 pm

Ann wrote: ↑Sat Jun 08, 2024 6:03 am There is a Hubble image of a portion of Pandora's Cluster, and I decided to compare it with the same part of the cluster as imaged by Webb.

And to the ~4:30 position of Description #2, there is a quite blue little cluster that is red in Webb. There are lots of tiny blue dots that are red in Webb; such a big difference. Why?

Well, the HST image is approximately "true color", taken with broad filters that are shifted only a little towards the longer wavelengths. The JWST image was made at wavelengths humans can't even see, which were then assigned to a false color palette. There's no reason to expect similar colors, or necessarily even the same color relationships between the two.

In the brightest foreground star, two of the six-fold diffraction spikes are split into two spikes. Why? I expect that the six-fold spikes arise from the edges of the hexagonal mirror segments; if so, whence those two sub-spikes? (Note, I'm not referring to the smaller pair of spikes which are horizontal in that same image; they are caused by the secondary mirror support.)

JohnD wrote: ↑Sat Jun 08, 2024 10:43 am APoD,
Thank you for the link to the NASA video about the picture, which mentions the Red Dot (last 25 seconds) whose nature is unknown. In showing the Dot, the camera zoomed into the image, revealing multiple faint dots all over the dark sky between the stars and galaxies. They seemed to be white so not even more distance objects than the many red-shifted galaxies. What are these? Artefacts?

John

Yes, the red dot featured in the linked 2-minute video is intriguing. I would love to hear some additional thoughts on what it might be.
Russ

richardschumacher wrote: ↑Sat Jun 08, 2024 3:45 pm In the brightest foreground star, two of the six-fold diffraction spikes are split into two spikes. Why? I expect that the six-fold spikes arise from the edges of the hexagonal mirror segments; if so, whence those two sub-spikes? (Note, I'm not referring to the smaller pair of spikes which are horizontal in that same image; they are caused by the secondary mirror support.)

The information suggests this image was made with data from just one camera. However, if that isn't the case, I note that the intrinsic rotation between the NIRCam and MIRI instruments is quite close to the apparent angle between these diffraction spikes. Another possibility stems from the fact that the aperture position angle is variable with the JWST, and this image was made across multiple sessions, so it's possible that they weren't all made with perfectly matching rotation angles. Aligning the images would then duplicate or smear diffraction spikes.

zendae wrote: ↑Sat Jun 08, 2024 3:09 pm

Ann wrote: ↑Sat Jun 08, 2024 6:03 am There is a Hubble image of a portion of Pandora's Cluster, and I decided to compare it with the same part of the cluster as imaged by Webb.

And to the ~4:30 position of Description #2, there is a quite blue little cluster that is red in Webb. There are lots of tiny blue dots that are red in Webb; such a big difference. Why?

What Chris said to you is correct, of course. I'd like to weigh in with another suggestion. I believe that many of the little blue dots are tiny and distant vigorously starforming galaxies. I believe (and I may be wrong here, but I like to believe it) that these small blue galaxies are, in many cases at least, strongly dominated by big massive stars producing huge amounts of ultraviolet light. In other words, many of these "blue" galaxies should really be called ultraviolet instead.

But on their way to the Earth, the ultraviolet light from these stars is stretched, in many cases so that the ultraviolet light is redshifted into the blue part of the spectrum. Another possibility is, of course, what Chris said, namely that many of these blue galaxies are not distant enough to have their light strongly redshifted, so they are intrinsically blue and they look blue to Hubble.

But most of these blue galaxies will be very dusty, because vigorous star formation produces a lot of dust.

JWST can't detect blue wavelengths at about 400-500 nm, but it is very good at detecting dust. Dust is probably shown as red by the people processing the JWST images.

So therefore: Hubble detects the blue light that the blue galaxies emits, but JWST detects the large amounts of dust that are typically found in starforming galaxies.


Ann

Ann, is the mysterious "red dot" seen in the video seen in either of the labeled images you posted? Also, I can't seem to orient and locate your images, OR the "red dot" on today's APOD. <sigh>

johnnydeep wrote: ↑Sat Jun 08, 2024 6:37 pm Ann, is the mysterious "red dot" seen in the video seen in either of the labeled images you posted? Also, I can't seem to orient and locate your images, OR the "red dot" on today's APOD. <sigh>

Here is the red dot:


And you can see the red dot in the video some five seconds before it cuts out. The red dot is at upper center left.


Ann

johnnydeep wrote: ↑Sat Jun 08, 2024 6:37 pm Ann, is the mysterious "red dot" seen in the video seen in either of the labeled images you posted? Also, I can't seem to orient and locate your images, OR the "red dot" on today's APOD. <sigh>

If we're talking about the red dot at 1:00, I see it left of the galaxy circled in white:

Christian G. wrote: ↑Sat Jun 08, 2024 7:22 pm

johnnydeep wrote: ↑Sat Jun 08, 2024 6:37 pm Ann, is the mysterious "red dot" seen in the video seen in either of the labeled images you posted? Also, I can't seem to orient and locate your images, OR the "red dot" on today's APOD. <sigh>

If we're talking about the red dot at 1:00, I see it left of the galaxy circled in white:

Thanks - that's it alright! But I don't see it in Ann's reply images. Here's the side-by-side with the movie still and Ann's labeled image, with a dotted green line relating them:

johnnydeep wrote: ↑Sat Jun 08, 2024 9:13 pm

Christian G. wrote: ↑Sat Jun 08, 2024 7:22 pm

johnnydeep wrote: ↑Sat Jun 08, 2024 6:37 pm Ann, is the mysterious "red dot" seen in the video seen in either of the labeled images you posted? Also, I can't seem to orient and locate your images, OR the "red dot" on today's APOD. <sigh>

If we're talking about the red dot at 1:00, I see it left of the galaxy circled in white:

Thanks - that's it alright! But I don't see it in Ann's reply images. Here's the side-by-side with the movie still and Ann's labeled image, with a dotted green line relating them:


pandora cluster mystery dod.jpg

The red dot is located at number 3 in my annotated image. You have put it at number 10.

The red dot is quite faint and only looks bright in the enlarged image.

Ann

Ann wrote: ↑Sun Jun 09, 2024 3:44 am

johnnydeep wrote: ↑Sat Jun 08, 2024 9:13 pm

Christian G. wrote: ↑Sat Jun 08, 2024 7:22 pm

If we're talking about the red dot at 1:00, I see it left of the galaxy circled in white:

Thanks - that's it alright! But I don't see it in Ann's reply images. Here's the side-by-side with the movie still and Ann's labeled image, with a dotted green line relating them:


pandora cluster mystery dod.jpg

The red dot is located at number 3 in my annotated image. You have put it at number 10.

The red dot is quite faint and only looks bright in the enlarged image.

Ann

But that's not the red dot from the video. That red dot is near your "10" label as shown in Christian G.'s post above.

johnnydeep wrote: ↑Sun Jun 09, 2024 4:57 pm

Ann wrote: ↑Sun Jun 09, 2024 3:44 am

johnnydeep wrote: ↑Sat Jun 08, 2024 9:13 pm

Thanks - that's it alright! But I don't see it in Ann's reply images. Here's the side-by-side with the movie still and Ann's labeled image, with a dotted green line relating them:


pandora cluster mystery dod.jpg

The red dot is located at number 3 in my annotated image. You have put it at number 10.

The red dot is quite faint and only looks bright in the enlarged image.

Ann

But that's not the red dot from the video. That red dot is near your "10" label as shown in Christian G.'s post above.

Christian G. and I are talking about different red dots.

Ann

Ann wrote: ↑Sun Jun 09, 2024 5:21 pm

johnnydeep wrote: ↑Sun Jun 09, 2024 4:57 pm

Ann wrote: ↑Sun Jun 09, 2024 3:44 am

The red dot is located at number 3 in my annotated image. You have put it at number 10.

The red dot is quite faint and only looks bright in the enlarged image.

Ann

But that's not the red dot from the video. That red dot is near your "10" label as shown in Christian G.'s post above.

Christian G. and I are talking about different red dots.

Ann

Evidently, but both Christian G. and I were only talking about the "mystery" red dot from the video. At least as far as I can determine from reviewing the thread again. Anyway, this (russet) horse has now received quite enough of a beating from me. Time to move on.