Astronomers have tracked down a gigantic, previously unknown assembly of galaxies located almost seven billion light-years away from us. The discovery, made possible by combining two of the most powerful ground-based telescopes in the world, is the first observation of such a prominent galaxy structure in the distant Universe, providing further insight into the cosmic web and how it formed.
“Matter is not distributed uniformly in the Universe,” says Masayuki Tanaka from ESO, who led the new study. “In our cosmic vicinity, stars form in galaxies and galaxies usually form groups and clusters of galaxies. The most widely accepted cosmological theories predict that matter also clumps on a larger scale in the so-called ‘cosmic web’, in which galaxies, embedded in filaments stretching between voids, create a gigantic wispy structure.”
These filaments are millions of light years long and constitute the skeleton of the Universe: galaxies gather around them, and immense galaxy clusters form at their intersections, lurking like giant spiders waiting for more matter to digest. Scientists are struggling to determine how they swirl into existence. Although massive filamentary structures have been often observed at relatively small distances from us, solid proof of their existence in the more distant Universe has been lacking until now.
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Does this imply a continuous network, web or skeleton of the universe? What are the cosmological implications of this discovery?
"The most widely accepted cosmological theories predict that matter also clumps on a larger scale in the so-called ‘cosmic web’, in which galaxies, embedded in filaments stretching between voids, create a gigantic wispy structure....
These filaments are millions of light years long and constitute the skeleton of the Universe: galaxies gather around them, and immense galaxy clusters form at their intersections, ..."
Originally Posted by Astronuc
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Does this imply a continuous network, web or skeleton of the universe? What are the cosmological implications of this discovery?
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It certainly is a very interesting discovery, and by no means a new one!
We were seeing pictures of the wispy cobwebby structure already 10 years ago. And the formation of such structures is a central part of the accepted theory of structure formation in the early universe.
Here is a 2001 press release about the observation of the wispy cobwebby structure, which was earlier predicted by models. This wouldn't be the earliest appearance of the idea, just a sample: http://www.eso.org/public/outreach/p.../pr-11-01.html
One of the important implications has to do with dark matter. People do computer models of the formation of structure, where matter (most of it dark) is allowed to condense from near-uniformity (by ordinary gravity) and they find the simulations give pictures that look pretty much like what we observe!
The dark matter---because so much of it, it dominates---is what condenses into strands---and denser regions where strands intersect. Then the ordinary matter (only about 1/10 as much) is attracted to these concentrations of dark matter and collects along these strands and especially at intersections---and it is what we see.
Structure formation computer modeling (and it's striking agreement with observation) is one of a several interlocking kinds of evidence supporting the assumption of dark matter.
One of the places one can see these computer simulations of early universe structure formation is in the popular TED lecture by George Smoot. Google "TED Smoot". It is only 15-20 minutes and it's well worth watching the whole thing.
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A further question is what can we expect to learn from this newly reported 2009 observation of a particular wisp at redshift z = 0.55?
Presumably other things like this have been detected and they lend themselves to technical refinements of detail.
Here is the Tanaka et al. abstract: http://www.aanda.org/index.php?optio...6361/200912929
They say "The observed structure is among the richest ever observed in the distant Universe. They will be an ideal site for quantifying environmental variations in the galaxy properties and effects of large-scale structure on galaxy evolution."
Here is the Tanaka et al. preprint: http://arxiv.org/abs/0909.3163
The spectroscopically confirmed huge cosmic structure at z=0.55
Each dot is a galaxy, the distance to the right and left are distances from earth above and below the galactic plane (the region we can see). I think this is one of the best cosmology pictures that exists, you can see this "web" very well.... amazing, really.
Just a BTW comment, I was happy to see that the ESO press release used the present-day distance---the distance used in working astro and cosmology. They did not use "light travel time" interpreted as a distance. We should encourage this among ourselves.
If you plug z = 0.55 into wright's calculator you get that the distance NOW to the structure is 6.7 billion lightyears.
That would be the radar distance if you could freeze expansion today and send a signal to it.
And ESO said "nearly 7 billion light years." Clearly they had that 6.7 in mind.
On the other hand the calculator will also tell you that the light travel time was 5.4 billion years. Light travel time is not related in any simple fixed way to actual distance, because the expansion rate has varied considerably over time. Since they said 7 billion lightyears, they could not have had the travel time (of 5.4 billion years) in mind.
There is a website that caters to middle-schoolers (and younger teens in general) that used to use light travel time as an expression for distance, this contributed to confusion---but I think they may have cleared that up somewhat recently. For astronomers and most of the rest of us, distance is normally actual distance (with expansion frozen at some definite time so that it can be well-defined.)
This, IMO, is misleading marcus. Submarines use sound travel time to compute the future distance and position of other ships. If this approach is flawed, how do they hit their targets? Sound travel time is used to compute the 'now' distance and predict the future distance. Light travel time is no different.
Hey Mikey thanks for posting that image. As well I'd have to agree with Chronos... as long as it is made clear which distance method is used it won't make a difference... will it? (aside from the obvious difference in the numerical value)
@OP
Astronuc as you can see from the many posts here the web structure has been observed for quite sometime. A lot of simulations you can find on youtube show this web structure in 3D...
When I first saw this simulation it blew my mind away.
On the other hand the calculator will also tell you that the light travel time was 5.4 billion years. Light travel time is not related in any simple fixed way to actual distance, because the expansion rate has varied considerably over time. Since they said 7 billion lightyears, they could not have had the travel time (of 5.4 billion years) in mind.
There is a website that caters to middle-schoolers (and younger teens in general) that used to use light travel time as an expression for distance, this contributed to confusion---but I think they may have cleared that up somewhat recently. For astronomers and most of the rest of us, distance is normally actual distance (with expansion frozen at some definite time so that it can be well-defined.)
(emphasis mine)
I'm sure ESO could have used any distance measure they wanted in the press release, all that matters is that it is in the Billions and a big number. But you're right, it looks they are using the transverse Proper distance as defined by FRW co-ordinates for this.
But please don't use phrases like 'the actual distance' to describe this quantity. It is no more special, unique or correct than any other distance, and to say that it is is thoroughly misleading. It's perfectly acceptable, and probably true, to say that this might be the simplest, easiest to understand and most usefull distance to use at a pop sci level, but stop there!
Let me make this clear, cosmologists do not use the transverse proper distance as defined by FRW co-ordinates when talking to each other! You would only use measureable distances for this, such as angular diameter distance, luminosity distance or redshift. What ESO uses to convert these into some distance for a press release should not be interpreted as saying anything about scientific discourse. For starters, you have to assume a set of cosmological parameters (I know you understand all this) which makes this distance ambigous and prone to revision in a way that measurable distances are not.
I've read probably hundreds of cosmology papers and attended at least a dozen or so cosmology conferences. I've still yet to see a distance be communicated by the tranverse proper distance in co-moving co-ordinates, which would be surprising if indeed this was the correct 'actual distance'....
(note to be clear: 'Proper distance' is a technical term, it doesn't imply a unique or correct description. In fact the definition of this distance requires arbitrary gauge choices to be defined).
@OP
Astronuc as you can see from the many posts here the web structure has been observed for quite sometime. A lot of simulations you can find on youtube show this web structure in 3D...
It was my impression that the web structure has been studied for sometime, although it's not something I follow closely. I believe SpaceTiger did his PhD on a certain large structure or set of large structures.
I had read a Yahoo article from Space.com, so I went to ESO's site for the actual story. I thought it might be of interest here, and that more knowledgable folks here could provide more insight into the significance of the 'new' discovery and how it fits with the 'known' web/skeleton.
There have been suggestions that the filamentous structures could imply a fractal distribution of matter, as well. Self-similarity might not play well with the observed near-by Fingers of God effect, nor with the Kaiser effect, which is observed on more distant systems. Both effects might point to an inconsistency or unexplained contribution to redshift that is not normally assumed by the effects expected from the Hubble distance/redshift relation, nor the contributions explainable by the Doppler effects resulting from the peculiar motions of the galaxies.
There have been suggestions that the filamentous structures could imply a fractal distribution of matter, as well. Self-similarity might not play well with the observed near-by Fingers of God effect, nor with the Kaiser effect, which is observed on more distant systems. Both effects might point to an inconsistency or unexplained contribution to redshift that is not normally assumed by the effects expected from the Hubble distance/redshift relation, nor the contributions explainable by the Doppler effects resulting from the peculiar motions of the galaxies.
Woah turbo I never knew you knew stuff about cosmology .
@Astro. Sorry I thought you meant that the new information was suggesting our universe is of what structure.
There have been suggestions that the filamentous structures could imply a fractal distribution of matter, as well. Self-similarity might not play well with the observed near-by Fingers of God effect, nor with the Kaiser effect, which is observed on more distant systems. Both effects might point to an inconsistency or unexplained contribution to redshift that is not normally assumed by the effects expected from the Hubble distance/redshift relation, nor the contributions explainable by the Doppler effects resulting from the peculiar motions of the galaxies.
On the contrary, the web like structure has long been a prediction from simulations assuming the standard model. The continued observational evidence for its existence is further evidence in favour of the standard model then, and not evidence for anomalies or inconsistencies as you suggest.
On the contrary, the web like structure has long been a prediction from simulations assuming the standard model. The continued observational evidence for its existence is further evidence in favour of the standard model then, and not evidence for anomalies or inconsistencies as you suggest.
Filamentous structure was discovered through surveys, as was the existence of "walls" of galaxies and voids. Once such structures are observed, cosmologists employ computer simulations to see if the existence of the structures can be accommodated within current models, including some hierarchical models of matter formation. Plausible accommodation should not be construed as "prediction".
The apparent distortion of clusters is another matter entirely. When we map nearby clusters of galaxies, we find that galaxies near the center of the clusters are preferentially blueshifted WRT to the other cluster members. If we map the galaxies' distances using their redshifts, this gives us maps in which the cluster assumes the appearance of a wedge, with the central galaxies at the cusp, and pointed directly at us (the observers). This was not expected. It is assumed that in a virialized cluster, smaller members held in the gravitational sway of the larger members would have a wide range of peculiar motions, including some with substantial motion toward us or away from us (blueshifted and redshifted, respectively). This is not observed. Instead, we get the Fingers of God effect in which the redshift distributions of the cluster members make them appear to be distributed preferentially with respect to the observer. Central members closer to us (using redshift=distance model) and outlying members farther from us. The opposite effect (Kaiser effect) is observe in distant clusters, with the cluster maps assuming a flattened shape.
Filamentous structure was discovered through surveys, as was the existence of "walls" of galaxies and voids. Once such structures are observed, cosmologists employ computer simulations to see if the existence of the structures can be accommodated within current models, including some hierarchical models of matter formation. Plausible accommodation should not be construed as "prediction".
Sorry Turbo, but this is simply incorrect. N-body simulations were predicting the cosmic web a decade before we were able to see it is things like the 2DFGRS and SDSS surveys. It's a basic prediction of not just LCDM but more broadly any FRW like model with an effective tilt in the power spectrum of fluctuations in the range that we observe. The earliest simulations in the 1980's (e.g. Efstathiou and collaborators) showed this kind of structures, long before we had large galaxy surveys.
Originally Posted by turbo-1
The apparent distortion of clusters is another matter entirely. When we map nearby clusters of galaxies, we find that galaxies near the center of the clusters are preferentially blueshifted WRT to the other cluster members. If we map the galaxies' distances using their redshifts, this gives us maps in which the cluster assumes the appearance of a wedge, with the central galaxies at the cusp, and pointed directly at us (the observers). This was not expected. It is assumed that in a virialized cluster, smaller members held in the gravitational sway of the larger members would have a wide range of peculiar motions, including some with substantial motion toward us or away from us (blueshifted and redshifted, respectively). This is not observed. Instead, we get the Fingers of God effect in which the redshift distributions of the cluster members make them appear to be distributed preferentially with respect to the observer. Central members closer to us (using redshift=distance model) and outlying members farther from us. The opposite effect (Kaiser effect) is observe in distant clusters, with the cluster maps assuming a flattened shape.
This is also not at all true. The 'Fingers of God' simply refers to line of sight redshift space distortions, which are observed in surveys in much the same way as you get from simulations (or even just expectations from perturbation theor). We have even used these red-shift space distortions to learn some reasonably accurate things about dark energy. See for instance the Nature paper by Guzzo et al. There is no discrepancy between theory and observations along the lines of what you are suggesting. If you have any references to the contrary please share them, but I could give you dozens of references looking at redshift space distortions and their value to cosmology, and in no study I've seen has anything like this been shown to be a significant issue.
On the contrary, the web like structure has long been a prediction from simulations assuming the standard model. The continued observational evidence for its existence is further evidence in favour of the standard model then, and not evidence for anomalies or inconsistencies as you suggest.
The interesting thing about science is what constitutes the "standard model" changes over time. In the 1980's, there were two competing models for the cosmology. Cold dark matter and hot dark matter. If the dark matter is cold, then you should see very complicated structures like what we do see. If the dark matter is hot, then you shouldn't because the thermal movement of the dark matter would wipe out these structures. (Imaging throwing an ice crystal into boiling water.)
Physics cage fighting. Two competing theories. Look at the observations. One theory dies. The other gets the "standard model" crown.
Depending on the temperature you assume for the hot dark matter, you'd still see filamentary like structures forming (unless it was really hot). Really, it is quite a generic prediction of non-linear gravitational structure formation in an expanding Universe, it doesn't actually tell you that much about the physics of say dark energy or dark matter etc since you get this kind of structure in a very wide parameter range.
Also it's not just filament structure, but the *type* of filament structure. You run statistics on the the N-body simulations, get a number. Run statistics on observations, get another number. See if the numbers match.
It's really important to use statistics to do these sorts of comparisons since "gee the pictures look the same/different" doesn't work very well.
Also IIRC the statistics that you see are pretty clearly non-fractal, as the power spectrum doesn't show any self-similarity.
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