Several superclusters revealed by the 2dF Galaxy Redshift Survey.

Examining the Great Wall

Article written: 10 May , 2011
Updated: 24 Dec , 2015
by

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Structure exists on nearly all scales in the universe. Matter clumps under its own gravity into planets, stars, galaxies, clusters, and superclusters. Beyond even these in scale are the filaments and voids. The largest of these filaments is known as the Sloan Great Wall. This giant string of galaxies is 1.4 billion light years across making it the largest known structure in the universe. Yet surprisingly, the Great Wall has never been studied in detail. Superclusters within it have been examined, but the wall as a whole has only come into consideration in a new paper from a team led by astronomers at Tartu Observatory in Estonia.

The Sloan Great Wall was first discovered in 2003 from the Sloan Digital Sky Survey (SDSS). The survey mapped the position of hundreds of millions of galaxies revealing the large scale structure of the universe and uncovering the Great Wall.

Within it, the wall contains several interesting superclusters. The largest of these SCl 126 has been shown previously to be unusual compared to superclusters within other large scale structures. SCl 126 is described as having an exceptionally rich core of galaxies with tendrils of galaxies trailing away from it like an enormous “spider”. Typical superclusters have many smaller clusters connected by these threads. This pattern is exemplified by one of the other rich superclusters in the wall, SCl 111. If the wall is examined in only its densest portions, the tendrils extending away from these cores are quite simple, but as the team explored lower densities, sub filaments became apparent.

Another way the team examined the Great Wall was by looking at the arrangement of different types of galaxies. In particular, the team looked for Bright Red Galaxies (BRGs) and found that these galaxies are often found together in groups with at least five BRGs present. These galaxies were often the brightest of the galaxies within their own groups. As a whole, the groups with BRGs tended to have more galaxies which were more luminous, and have a greater variety of velocities. The team suggests that this increased velocity dispersion is a result of a higher rate of interactions among galaxies than in other clusters. This is especially true for SCl 126 where many galaxies are actively merging. Within SCl 126, these BRG groups were evenly distributed between the core and the outskirts while in SCl 111, these groups tended to congregate towards the high density regions. In both of these superclusters, spiral galaxies comprised about 1/3 of the BRGs.

The study of such properties will help astronomers to test cosmological models that predict galactic structure formation. The authors note that models have generally done a good job of being able to account for structures similar to SCl 111 and most other superclusters we have observed in the universe. However, they fall short in creating superclusters with the size, morphology and distribution of SCl 126. These formations arise from density fluctuations initially present during the Big Bang. As such, understanding the structures they formed will help astronomers to understand these perturbations in greater detail and, in turn, what physics would be necessary to achieve them. To help achieve this, the authors intend to continue mapping the morphology of the Sloan Great Wall as well as other superclusters to compare their features.

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30 Responses

  1. Anonymous says

    Funny isn’t it that these great strings of galaxies across vast regions of space have been discovered using redshifts. Deniers often point out that these galaxies are lines of magnetic fields, in infinite universe, yet also deny how they were discovered and whose very existence relies on redshifts produced by the expanding universe and the Big Bang. Bizarrely, they also deny the Big Bang starting the universe 13.7 billion years ago.

    These superclusters are clearly vestiges of the early universe, who tell the underlying story of galaxy formation. It is good that the redshift work continues, and in time, we might get a better picture of the much finer details of the structures.

    • Paul Cook says

      Not so fast. We know the speed at which the Great Wall has formed (and is moving) and to have gotten where it is now has taken about 90 billion years to form. This isn’t a vestige of the early universe. The early universe according to the Big Bang theory was all homogenous plasma (before inflation) with no holes or voids. The BB theory cannot explain the voids or the uneven distribution of matter (and energy) in our current universe, even with inflation.

      • Torbjörn Larsson says

        No, EUPCExterminator has it right. The observable universe is ~ 14 Gy but its radius is ~ 45 Gly due to its expansion.

        Nor where there a plasma before inflation, particles were first formed under reheating after inflation.

        As for structure formation, inflation blew up quantum fluctuations to seed what we can observe as large scale structures today (galaxy clusters, CMB nonuniformities). As the universe expanded the fluctuations expanded with it, hence the universe before inflation was roughly as inhomogenous per volume as it is today.

        It is wrong to claim that todays cosmology does not predict any of this, because it is precisely what if does. You can look it up in Wikipedia, say.

  2. Justin Hartberger says

    “The authors note that models have generally good job…” should that be “have generally done a good job”?

  3. Anonymous says

    I don’t like the new comments sections. Looks confusing and I have the impression that it is spammed by twitter accounts. Basically unreadable.

  4. Todd says

    A question I’ve always wondered about … Are these structures real? I mean: they span several tens of light megayears, but they aren’t all in the same place at the same time as we seen them, are they? A “wall” tilted at an angle from the perspective of the Earth will be stretched out. We can only be sure of a structure who components are generally at the same distance from our perspective.

  5. Todd says

    A question I’ve always wondered about … Are these structures real? I mean: they span several tens of light megayears, but they aren’t all in the same place at the same time as we seen them, are they? A “wall” tilted at an angle from the perspective of the Earth will be stretched out. We can only be sure of a structure who components are generally at the same distance from our perspective.

    • Todd, these structures are real. We can’t be sure any of it is really there because we could simply be looking at vestiges of light from objects that disappeared eons ago but it is more likely that the things that made the light are still around. That being said, why should they be in the same place? If the red shift is constant for a given set of galaxies, then , oh geez, now I can’t see what I’m writing…sigh, Fraaaaser!!!

    • Torbjörn Larsson says

      Yes, it seems hard to elucidate, but there are distance markers that place things. I’m sure you can get hold of the uncertainties in the published maps if you look for it.

      Also, it is meaningless to discuss “same place” and “same time” for (astronomically) extended objects and/or events according to general relativity. It is IMHO better to think of it as a composite of individual observations than a snapshot of a perspective.

    • Torbjörn Larsson says

      Yes, it seems hard to elucidate, but there are distance markers that place things. I’m sure you can get hold of the uncertainties in the published maps if you look for it.

      Also, it is meaningless to discuss “same place” and “same time” for (astronomically) extended objects and/or events according to general relativity. It is IMHO better to think of it as a composite of individual observations than a snapshot of a perspective.

  6. The scientists found 13 more clusters embedded in a large-filamentary network, and have made some incredible statements concerning the cosmic web of dark matter, in their paper, which is titled “Mass, Light, and Colour of the Cosmic Web in the Supercluster SCL2243-0935 (z=0.447). They state that “The filaments we study in SCL2243 are a larger magnitude size, REPRESENTING THE ACTUAL COSMIC WEB.” They also state “in N-body simulations, the term FILAMENT is used to DESCRIBE the low-density diffuse DARK MATTER component connecting one or several galaxy clusters.” “In a filament, more or less distinct groups and smaller clusters of galaxies can form, TRACING THE UNDERLYING DARK MATTER FILAMENT.” “We also refer to the optical structures as filaments.” They say, “filaments are difficult to detect given their low surface mass density, and that “ACDM models agree that most mass of the Universe is in filaments, with galaxy clusters second.

    Can someone please explain to me, if these filaments are so widespread and account for more mass then anything else, why is calling the cosmic web “dark matter”, necessary? Wouldn’t the EM forces involved with the filaments somehow be responsible for causing the gravity requirements for the missing dark matter? Aren’t filaments surrounded and confined by huge magnetic fields, with an electric current that is perpendicular to the magnetic field? Wouldn’t Faraday’s Law of charges in motion in space apply to filaments?

    Thank you,

    • Member
      Anonymous says

      They’re comparing Nbody simulations to the real universe. In the simulations, the blobs represent dark matter and often form into these filamentary structures and provide the scaffolding for the physical matter we actually observe. As a result, we physically see them as strings of galaxies as I described in this article. However, even though we only see the baryonic matter, the dark matter still envelops it and makes up most of the mass.

      And no, your electric universe crap still doesn’t make sense here.

      • you’re just a science writer jon. Filaments are observed and expected to fill the universe. you want to believe that some kind of hypothetical dark matter envelops the magnetized plasma filaments, and has huge missing mass and gravity. Stop using fowl language Mr voisey.

      • Anonymous says

        Oh please. And no, your electric universe crap still doesn’t make sense here.

      • Torbjörn Larsson says

        No. we don’t “want to believe” as anyone actually reading Jon’s comment notes. It is predicted by simulations being faithful to standard cosmology that gets the universe correct and consistent (for the first time), including dark matter and structure formation.

      • Anonymous says

        It is foul language, not the chicken-splitting like fowl language.
        (After you own haughty words on a recently deleted post, you’re already lucky to be here! Be careful, Mr, Hologram, be very careful!.)

    • Anonymous says

      Mr. Hologram (not being so rude this time) yet again returns in yet another deliberately misrepresenting avatar name.
      To simply answer to your question is; Not on your nelly is this correct.

    • Anonymous says

      “Cosmologist”. You are no cosmologist.
      This really misrepresents the truth

    • Anonymous says

      Read this + linked article “Intergalactic Filaments as Isothermal Gas Cylinders” by Hartford & Hamilton (as of yesterday) http://arxiv.org/pdf/1012.1293

      Conclusion

      “From a comological hydrodynamic simulation at redshift 5, we find that a plausible model for intergalactic filaments is an isothermal gas cylinder whose structure and stability are determined primarily by the gravitational and hydrody- namic properties of the gas. The cylinders have a central gas density of several hundred times the mean total cosmic density, with a peak at about 500. The average temperature of the gas in the cylinders is 1-2 times 10^4 K. The neutral hydrogen fraction is generally between 0.01 and 0.02.” and
      “We reasoned that these contrasting distributions of gas and dark matter result from hydrodynamic effects: pressure forces retard the gas as it moves toward the axis of a filament, in contrast to the dark matter which can pass freely through subject only to gravitational forces. The gas would be expected to accumulate along the axis of the filament until the pressure forces are sufficient to counteract the gravitational field. In this paper we explore the hypothesis that the gas in the baryonic core forms a self- gravitating, isothermal cylinder in hydrostatic equilibrium, whose structure is determined primarily by the gravitational and hydrodynamic properties of the gas.”

      From the images in this article (pg.2), they say;
      “Figure 1 shows the typical distributions of gas and dark matter about a filament. Each image shows actual simulation particles in a sub-box of the simulation. The top image shows just the gas particles, while the bottom image shows just the dark matter particles. Clearly the gas and dark matter have very different structures.”

      This clearly proves your completely wrong and crazy unsupported assumptions.

      Caveat lector delectatio morosa. (dum spiro. dura lex, sed lex.)

      (As an alleged ‘cosmologist’, you should easily account for the “Background and Rationale” (Section 2) and point out the flaws in the mathematical theory behind this. If you can’t you’ve just lost this argument, yet again.)

  7. Ramanan T says

    The universe and galaxies are like sponge. there are filaments and voids. When it expands the voids and filaments become large. At one point everything will come together. There will be a big crunch similar to big bang.

    • Torbjörn Larsson says

      Maybe, but then you need new physics replacing today’s. In standard cosmology the universe expands forever:

      “It foretells a future in which the metric expansion of space will carry all galaxies away from each other at speeds greater than light, and observers in each galaxy will see only their own galaxy in an otherwise empty universe.”

  8. Anonymous says

    The positions of elements in this structure are known by red shift. Other distance ruler measures are used to benchmark distance and velocity more locally. Further an SNIa further out at cosmological distance acts as a standard candle or ruler. So the Hubble relationship is understood with considerable confidence.

    LC

  9. Anonymous says

    The positions of elements in this structure are known by red shift. Other distance ruler measures are used to benchmark distance and velocity more locally. Further an SNIa further out at cosmological distance acts as a standard candle or ruler. So the Hubble relationship is understood with considerable confidence.

    LC

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