APOD: Pandora's Cluster of Galaxies (2023 Jun 09)

APOD Robot · Post by **APOD Robot** » Fri Jun 09, 2023 4:05 am

Pandora's Cluster of Galaxies

Explanation: This deep field mosaicked image presents a stunning view of galaxy cluster Abell 2744 from 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 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, 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.

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shaileshs · Post by **shaileshs** » Fri Jun 09, 2023 4:32 am

Very interesting and intriguing. I wonder - 1) how come this region seems to have sooooooooooooooooooooooo many "red shifted" (super old) galaxies behind the foreground galaxy cluster and what's their age (how old are they). Normally in other gravitational lensing photos, we tend to see lot more blue/yellow arcs .. and 2) I wonder how many are seen multiple times.. and 3) I'm amazed how telescope (and data processing ML algo) distinguish between so many sooooooooooo close galaxies, which ones are GL'ed and which ones not and those that are GL'ed, how many have multiple occurrences ... Uffff!

JohnD · Post by **JohnD** » Fri Jun 09, 2023 11:05 am

Since the stars in the constellation are in this galaxy, surely that should be, "three different massive galaxy clusters some 3.5 billion light-years away BEYOND the constellation Sculptor."?

Christian G. · Post by **Christian G.** » Fri Jun 09, 2023 1:02 pm

Mind-blowing image… And to think that, aside from a few local variations, no matter where you point JWST in the sky you would roughly get the same image, blows my mind tenfold!

richardschumacher · Post by **richardschumacher** » Fri Jun 09, 2023 1:40 pm

APOD Robot wrote: ↑Fri Jun 09, 2023 4:05 am
Explanation: Of course distinctive diffraction spikes mark foreground Milky Way stars.

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About those diffraction spikes: in today's image two of the spikes (the ones at the 12:00 and 2:00 positions) have distinctive sub-spikes. In the older telescope alignment image (linked in the quote above) there are no such sub-spikes. Why?

MRPUGH · Post by **MRPUGH** » Fri Jun 09, 2023 2:04 pm

Hi folks
a stunning image from JWST. Can anyone tell me what the FOV is?

thanks
Martin

Chris Peterson · Post by **Chris Peterson** » Fri Jun 09, 2023 2:23 pm

richardschumacher wrote: ↑Fri Jun 09, 2023 1:40 pm
APOD Robot wrote: ↑Fri Jun 09, 2023 4:05 am
Explanation: Of course distinctive diffraction spikes mark foreground Milky Way stars.

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About those diffraction spikes: in today's image two of the spikes (the ones at the 12:00 and 2:00 positions) have distinctive sub-spikes. In the older telescope alignment image (linked in the quote above) there are no such sub-spikes. Why?

Generally this type of artifact is seen when there's a bit of camera rotation between images, so the angle of the spikes changes with respect to the aligned background (keeping in mind that images like this are made by stacking and combining multiple exposures made through multiple filters). Of course, that should lead to all the spikes being duplicated, not just a pair of them. And I'm not sure about the rotational stability of JWST, that is, whether it maintains a highly fixed orientation or can vary a bit.

orin stepanek · Post by **orin stepanek** » Fri Jun 09, 2023 7:59 pm

More galaxies than I can count; and they were there, like forever!

Well as far as I'm concerned; forever!

Roeland · Post by **Roeland** » Fri Jun 09, 2023 8:44 pm

""At the Pandora Cluster's estimated distance this cosmic box spans about 6 million light-years."

This can't be correct. Maybe 60 million?

Roeland · Post by **Roeland** » Fri Jun 09, 2023 8:48 pm

Roeland wrote: ↑Fri Jun 09, 2023 8:44 pm ""At the Pandora Cluster's estimated distance this cosmic box spans about 6 million light-years."

Is this correct? Maybe 60 million?

Chris Peterson · Post by **Chris Peterson** » Fri Jun 09, 2023 9:29 pm

Roeland wrote: ↑Fri Jun 09, 2023 8:44 pm ""At the Pandora Cluster's estimated distance this cosmic box spans about 6 million light-years."

This can't be correct. Maybe 60 million?

6 million sounds reasonable. At a distance of 4 billion ly and a span of 6 million ly, that corresponds to a subtended angle of 5 arcmin. The NIRCam FOV is 2.2 arcmin for each of its pair of sensors.

VictorBorun · Post by **VictorBorun** » Fri Jun 09, 2023 11:02 pm

Chris Peterson wrote: ↑Fri Jun 09, 2023 9:29 pm
Roeland wrote: ↑Fri Jun 09, 2023 8:44 pm ""At the Pandora Cluster's estimated distance this cosmic box spans about 6 million light-years."

This can't be correct. Maybe 60 million?
6 million sounds reasonable. At a distance of 4 billion ly and a span of 6 million ly, that corresponds to a subtended angle of 5 arcmin. The NIRCam FOV is 2.2 arcmin for each of its pair of sensors.

We need to detail a convention.

My favourite is to label the picture of a distant galaxy or cluster a few billion ly away with metrics of the moment in time when the light was emitted. The angle size of that galaxy or cluster for an observer in the point where Milky Way is growing and Solar system might already exist was the same all the billions of years the photons were travelling, but the distance grew by (1+redshift) times.

So an angle size of 5 arcmin = 0.00145444 radians translates to 6 million ly at 4.14 billion ly distance at the moment the photons were emitted.
I am comfortable with the use of this measure of distance, but they usually publish other things.

4.14 billion ly of angular size distance converts to
redshift = 0.498
age (since the Big Bang) 8.642 billion years + light travel time 5.078 billion years = 13.72 our present age (since the Big Bang)
comoving radial distance, which is most popular, is 6.204 billion ly

VictorBorun · Post by **VictorBorun** » Fri Jun 09, 2023 11:11 pm

I wonder what the field of view is for background galaxy distribution and would-be filaments and clusters

It must be smaller than 6 million ly because for large redshifts the more the distance (comoving radial distance) the more the angular size of the observed object.

For a given angular size of the observed object: the more the distance (comoving radial distance) the less the size of the observed object.

I know it sounds wild, but it is so. The photons from the background galaxies had been for some time receding while moving our way through the space… because that space was flowing away from Milky Way at a greater speed. Later Hubble parameter got smaller and then those photons finally began to get closer to us.

alter-ego · Post by **alter-ego** » Sat Jun 10, 2023 5:02 am

VictorBorun wrote: ↑Fri Jun 09, 2023 11:11 pm I wonder what the field of view is for background galaxy distribution and would-be filaments and clusters

It must be smaller than 6 million ly because for large redshifts the more the distance (comoving radial distance) the more the angular size of the observed object.

For a given angular size of the observed object: the more the distance (comoving radial distance) the less the size of the observed object.

I know it sounds wild, but it is so. The photons from the background galaxies had been for some time receding while moving our way through the space… because that space was flowing away from Milky Way at a greater speed. Later Hubble parameter got smaller and then those photons finally began to get closer to us.

• Considering the current redshift record for JWST ≈ 13 (200 million years after BB), the relativistic FoV scale at that redshift = 3.53 kpc/arcsecond.
Assuming the NIRCam 5 arcmin instrument FoV, then the FoV at Z= 13 → 3.5 million ly.

• FYI, the present ΛCDM expansion theory predicts the Z = 13 (observed now) will reach a minimum redshift ≈ 10.3 in another 7.3 billion years when expansion acceleration begins to dominate. I.e. as observed now objects at Z = 13 will continue to slow down until acceleration takes over at a turning point about 7 billion years from now.

Christian G. · Post by **Christian G.** » Sat Jun 10, 2023 5:16 pm

orin stepanek wrote: ↑Fri Jun 09, 2023 7:59 pm abell2744_jwst1024.png
More galaxies than I can count

Indeed! And with reason, apparently there are some 50 000 near infrared light "sources" in that image. Not sure how many of those are galaxies but a whole lot, I suppose...

Sam · Post by **Sam** » Sun Jun 11, 2023 4:44 pm

Am reminded of xkcd's "Angular Diameter Turnaround":

https://xkcd.com/2622/

[Title text: Thank you to Katie Mack for teaching me about this effect, and to Janelle Shane for describing redshifts as 'like galaxies sinking into a pool of dilute blood,' which is how I'll see them from now on.]

Starship Asterisk*

APOD: Pandora's Cluster of Galaxies (2023 Jun 09)

APOD: Pandora's Cluster of Galaxies (2023 Jun 09)

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