Starship Asterisk*

In the final sentence in the explanation it states Abell 2744 "can best be seen with a really large telescope". That made me :) . So, size does matter :!:

PS. The APOD is a cropped version of the full released image that can be seen when clicking on the APOD or some of the links. To me there does not seem to be anything of significance gained here by using a cropped version and so I would prefer to see the image that was released.

Pandora Cluster of Galaxies is very great 2 millions of l. y.

[quote="garry"]With dark matter, I thought it was still a theory and still nota proven scientific fact. If in the APOD it is coloured blue, does this mean you can measure it? How do you measure a theory? A discrepancy perhaps?[/quote]


The dark matter in blue is an ESTIMATE based on what it would take to achieve the gravitational lensing effects, that normal matter does not add up to being able to do... supposedly. It is "INFERRED".

:------====== <-Smiley looking in telescope.

BRUTUS INQ: quid quid latine dictum sit, altum vivitur {si hoc legere scis nimium eruditionis habes} Ave!

[quote="orin stepanek"]

I was surprised to learn that clusters of galaxies would collide with other clusters.

Seems as though with the universe expanding; that they would be going away from each other. :?[/quote]
Hubble expansion [b][u]cannot[/u][/b] do work on (i.e., expand) gravitationally bound systems.

(Besides, Hubble expansion would only have amounted to just 50 km/s within the span of two million light years.)

Thank you for this impressive image and for the fascinating postings. Maximum enjoyment!
[i]doleo ergo sum[/i]

[quote="garry"]With dark matter, I thought it was still a theory and still nota proven scientific fact. If in the APOD it is coloured blue, does this mean you can measure it? How do you measure a theory? A discrepancy perhaps?[/quote]
Everything's a theory (or if you like, per Neufer, some things are hypotheses). There is no such thing as a proven scientific fact- that concept doesn't exist is science. Everything we measure, we measure indirectly and infer some sort of physical truth from our interpretation of that measurement.

Given the number of independent observations that can be explained by dark matter, few physicists doubt that it is real, even if it remains uncertain just what all of its actual physical properties are.

[quote="hickok_wild_b"]There is clearly a spaceship in the lower right[/quote]
Clearly, and at 3.5 billion light years away, it must be huge. :roll:

There is clearly a spaceship in the lower right

[quote="BMAONE23"]Did hubble images produce the more focused central region and the VLT images the less focused outside areas?[/quote]
[quote="[url=http://hubblesite.org/newscenter/archive/releases/2011/17/]HubbleSite[/url]"]... The image is a composite of separate exposures made by Hubble Space Telescope Advanced Camera for Surveys detectors in October 2009, the VLT, and the Chandra ACIS detector. Hubble provides the central, most detailed part of the image, while the VLT, which has a wider field of view, provides the outer parts of the image.[/quote]
[quote="bystander"][b][i]Abell 2744: Pandora’s Cluster — Clash of the Titans[/i][/b]
[b][i] http://asterisk.apod.com/viewtopic.php?f=31&t=24246 [/i][/b][/quote]

An interesting image to be certain. With the combination of Hubble Images and VLT Images being used to create the visible image I have to ask: Did hubble images produce the more focused central region and the VLT images the less focused outside areas?

I was surprised to learn that clusters of galaxies would collide with other clusters. Seems as though with the universe expanding; that they would be going away from each other. :?

[quote="bystander"]

Most of astrophysics is theory.[/quote]
Most of astrophysics is hypothesis; the best of astrophysics is theory.

[quote="garry"]With dark matter, I thought it was still a theory and still nota proven scientific fact. If in the APOD it is coloured blue, does this mean you can measure it? How do you measure a theory? A discrepancy perhaps?[/quote]
Most of astrophysics is theory. Yes, you can measure dark matter, or rather the effects of it. By measuring the "lensing effect", the amount of matter required to produce that effect can be computed. What matter isn't visible in emr is assumed to be dark matter ([url=http://arxiv.org/abs/1103.2772][b][i]arXiv:1103.2772[/i][/b][/url]).

[quote="bystander"][b][i]Abell 2744: Pandora’s Cluster — Clash of the Titans[/i][/b]
[b][i] http://asterisk.apod.com/viewtopic.php?f=31&t=24246 [/i][/b][/quote]

Remember the old Star Trek episodes, where alien intelligences made of clouds of energy roamed the Universe.
They looked exactly like this. Well, on my tv they did.
Gene Roddenberry, such a genius, Star Trek, Babylon 5, so predictive of the future.
Just waiting for the iCloud's communication and ultimatums.

[quote="APOD Robot"][url=http://apod.nasa.gov/apod/ap110629.html][img]http://apod.nasa.gov/apod/calendar/S_110629.jpg[/img] [size=150]Abell 2744: Pandoras Cluster of Galaxies[/size][/url][/quote]
[img3=""]http://www.disneylicious.com/i_04/wdcc_dumbo_clown_001.jpg[/img3]

With dark matter, I thought it was still a theory and still nota proven scientific fact. If in the APOD it is coloured blue, does this mean you can measure it? How do you measure a theory? A discrepancy perhaps?

[quote="Boomer12k"][quote="Jim Leff"]" Abell 2744, dubbed Pandora's cluster, spans over two million light years"

So this entire cluster spans just twenty Milky Ways (@100,000 light years in diameter)??[/quote]


Doesn't seem possible that all those galaxies are in the space between the Milky Way and The Andromeda Galaxy, 2.2-ish million light years. No wonder the gas is so hot.
I tried to search for the number of galaxies in the cluster, but could not find it. It is a said to be 3.5 billion light years away.[/quote]

I found a 2006 reference where the estimated total mass within 1 Mpc ≈1.5x10^15 M☉. Assuming the APOD link estimating galaxies amount to ≈5% (of the total mass) applies to the same region, and that our galaxy ≈1.5x10^11 M☉, then that works out to be a whopping 500 galaxies or so!

[quote="Jim Leff"]" Abell 2744, dubbed Pandora's cluster, spans over two million light years"

So this entire cluster spans just twenty Milky Ways (@100,000 light years in diameter)??[/quote]


Doesn't seem possible that all those galaxies are in the space between the Milky Way and The Andromeda Galaxy, 2.2-ish million light years. No wonder the gas is so hot.
I tried to search for the number of galaxies in the cluster, but could not find it. It is a said to be 3.5 billion light years away.

This is one of my favorite astronomical images of all time. To me, it represents the best of scientific thinking, to develop an approach to indirectly detect, and render as an image, a large region of dark matter. Great stuff!

" Abell 2744, dubbed Pandora's cluster, spans over two million light years"

So this entire cluster spans just twenty Milky Ways (@100,000 light years in diameter)??

The collision of four smaller clusters is going to be even and symmetrical? That is kind of limited thinking when we know now that the Universe is a chaotic place.

Who says the hot gas and dark matter distribution has to match? They are two different things. Two galaxies collide, their motion stalls as the gravity of both works to coalesce them together. Yet their dark matter continues on in the direction they were going like two remote control cars with marbles on them when they crash. The cars stop, but the marble fly off and keep going. So I would expect them to act differently. So of course four clusters collide and the distribution is different, and uneven, there are four of them!
And yet this whimsical stuff (dark matter) that keeps going is supposed to hold the galaxies together so everything spins at the same observed rate? And it is 75 percent of the mass in this picture? It is either of very much more mass and acts as one, or it is like neutrinos, so slight and small and different that it is barely affected by anything. Dark Matter is strange stuff indeed.

:------======= <-Smiley looking in telescope.

Finally! A place thats as confused as i am about everything. :mrgreen:

[b][i]Abell 2744: Pandora’s Cluster — Clash of the Titans[/i][/b]
[b][i] http://asterisk.apod.com/viewtopic.php?f=31&t=24246 [/i][/b]

[url=http://apod.nasa.gov/apod/ap110629.html][img]http://apod.nasa.gov/apod/calendar/S_110629.jpg[/img] [size=150]Abell 2744: Pandoras Cluster of Galaxies[/size][/url]

[b] Explanation: [/b] Why is this cluster of galaxies so jumbled? Far from a smooth distribution, [url=http://chandra.harvard.edu/photo/2011/a2744/]Abell 2744[/url] not only has knots of galaxies, but the [url=http://science.hq.nasa.gov/kids/imagers/ems/xrays.html]X-ray[/url] emitting hot gas (colored red) in the cluster appears distributed differently than the [url=http://en.wikipedia.org/wiki/Dark_matter]dark matter[/url]. The dark matter, taking up over 75 percent of the [url=http://en.wikipedia.org/wiki/Galaxy_groups_and_clusters]cluster[/url] mass and colored blue in the [url=http://hubblesite.org/newscenter/archive/releases/2011/17/image/a/]above image[/url], was inferred by that needed to create the distortion of background galaxies by [url=http://www.astrophysicsspectator.com/topics/generalrelativity/GravitationalLensPointSim.html]gravitational lensing[/url]. The [url=http://www.youtube.com/watch?v=qPE4ILbe4CM]jumble appears[/url] to result from the [url=http://www.youtube.com/watch?v=z6U_GFa76Ys]slow motion[/url] collision of at least four smaller galaxy clusters over the past few billion years. The above [url=http://imgsrc.hubblesite.org/hu/db/images/hs-2011-17-b-web_print.jpg]picture combines[/url] optical images from the [url=http://apod.nasa.gov/apod/ap010806.html]Hubble Space Telescope[/url] and the [url=http://apod.nasa.gov/apod/ap000707.html]Very Large Telescope[/url] with X-ray images from the [url=http://en.wikipedia.org/wiki/Chandra_X-ray_Observatory]Chandra[/url] X-Ray Observatory. [url=http://www.youtube.com/watch?v=WZ24B2qNhVQ]Abell 2744[/url], dubbed [url=http://en.wikipedia.org/wiki/Pandora%27s_box]Pandora[/url]'s cluster, spans over two million light years and can best be seen with a really large telescope toward the constellation of the [url=http://www.ianridpath.com/startales/sculptor.htm]Sculptor[/url].

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