Posted on by Nancy Atkinson

Hubble Studies Dark Matter Filament in 3-D

Hubble’s view of massive galaxy cluster MACS J0717.5+3745. The large field of view is a combination of 18 separate Hubble images. Credit:
NASA, ESA, Harald Ebeling (University of Hawaii at Manoa) & Jean-Paul Kneib (LAM)

Earlier this year, astronomers using the Hubble Space Telescope were able to identify a slim filament of dark matter that appeared to be binding a pair of distant galaxies together. Now, another filament has been found, and scientists a have been able to produce a 3-D view of the filament, the first time ever that the difficult-to-detect dark matter has been able to be measured in such detail. Their results suggest the filament has a high mass and, the researchers say, that if these measurements are representative of the rest of the Universe, then these structures may contain more than half of all the mass in the Universe.

Dark matter is thought to have been part of the Universe from the very beginning, a leftover from the Big Bang that created the backbone for the large-scale structure of the Universe.

“Filaments of the cosmic web are hugely extended and very diffuse, which makes them extremely difficult to detect, let alone study in 3D,” said Mathilde Jauzac, from Laboratoire d’Astrophysique de Marseille in France and University of KwaZulu-Natal, in South Africa, lead author of the study.

The team combined high resolution images of the region around the massive galaxy cluster MACS J0717.5+3745 (or MACS J0717 for short) – one of the most massive galaxy clusters known — and found the filament extends about 60 million light-years out from the cluster.

The team said their observations provide the first direct glimpse of the shape of the scaffolding that gives the Universe its structure. They used Hubble, NAOJ’s Subaru Telescope and the Canada-France-Hawaii Telescope, with spectroscopic data on the galaxies within it from the WM Keck Observatory and the Gemini Observatory. Analyzing these observations together gives a complete view of the shape of the filament as it extends out from the galaxy cluster almost along our line of sight.

The team detailed their “recipe” for studying the vast but diffuse filament. .

First ingredient: A promising target. Theories of cosmic evolution suggest that galaxy clusters form where filaments of the cosmic web meet, with the filaments slowly funnelling matter into the clusters. “From our earlier work on MACS J0717, we knew that this cluster is actively growing, and thus a prime target for a detailed study of the cosmic web,” explains co-author Harald Ebeling (University of Hawaii at Manoa, USA), who led the team that discovered MACS J0717 almost a decade ago.

Second ingredient: Advanced gravitational lensing techniques. Albert Einstein’s famous theory of general relativity says that the path of light is bent when it passes through or near objects with a large mass. Filaments of the cosmic web are largely made up of dark matter [2] which cannot be seen directly, but their mass is enough to bend the light and distort the images of galaxies in the background, in a process called gravitational lensing. The team has developed new tools to convert the image distortions into a mass map.

Third ingredient: High resolution images. Gravitational lensing is a subtle phenomenon, and studying it needs detailed images. Hubble observations let the team study the precise deformation in the shapes of numerous lensed galaxies. This in turn reveals where the hidden dark matter filament is located. “The challenge,” explains co-author Jean-Paul Kneib (LAM, France), “was to find a model of the cluster’s shape which fitted all the lensing features that we observed.”

Finally: Measurements of distances and motions. Hubble’s observations of the cluster give the best two-dimensional map yet of a filament, but to see its shape in 3D required additional observations. Colour images [3], as well as galaxy velocities measured with spectrometers [4], using data from the Subaru, CFHT, WM Keck, and Gemini North telescopes (all on Mauna Kea, Hawaii), allowed the team to locate thousands of galaxies within the filament and to detect the motions of many of them.

A model that combined positional and velocity information for all these galaxies was constructed and this then revealed the 3D shape and orientation of the filamentary structure. As a result, the team was able to measure the true properties of this elusive filamentary structure without the uncertainties and biases that come from projecting the structure onto two dimensions, as is common in such analyses.

The results obtained push the limits of predictions made by theoretical work and numerical simulations of the cosmic web. With a length of at least 60 million light-years, the MACS J0717 filament is extreme even on astronomical scales. And if its mass content as measured by the team can be taken to be representative of filaments near giant clusters, then these diffuse links between the nodes of the cosmic web may contain even more mass (in the form of dark matter) than theorists predicted.

More info in this ESA HubbleCast video:

Source: ESA Hubble

14 Replies to “Hubble Studies Dark Matter Filament in 3-D”

  2. As Spock would say: Fascinating. Is this not similar to the way neurons in the brain are connected – along filaments? My biology knowledge is minimal.

    1. The geometry is similar. Both are fractal geometries and they probably have close Hausdorff dimensions. However, these filaments of dark matter do not communicate action potentials or any type of signal between galaxies. LC

      1. Cool, thanks. Yes, it’s the geometry I was focusing on. It’s interesting to me to think of the universe as a big brain-like structure instead of an expanding balloon. Now wouldn’t it be something to discover that we could actually somehow send signals along dark matter filaments?? Get galaxies chatting with each other.

      2. It must be remembered that this filament is 60 million light years in length. A signal transmitted from one end to the other takes almost as much time as has elapsed since the end of the Cretaceous period. Since it is composed of dark matter it is hard to get anything to interact with it. Getting a handle on dark matter is rather tough to begin with. Since it does not interact by electromagnetic interactions it is hard to get a hold of. There is dark matter passing through us now, where if it interacts with ordinary matter at all it does so through the weak interaction, and of course there is gravity that is even weaker. The stuff consists of particles, or most likely so, and these particles should largely turn out to be neutralinos. These are the superpartners of the Z, photon and Higgs in a condensate since these superpartners carry the same quantum numbers. The interaction cross section is ~ 1/M^2 where the mass on the order of a TeV. This means they will interact with about a billion billionth the interaction strength of neutrinos, which are already difficult to get a handle on. There is some prospect that neutrino detectors might pick up a signal of a weakly interacting particle with signatures which depart from the neutrino. The LHC might also produce them where loss of s-channel information might bear the signatures of neutralinos. The FERMI spacecraft has found a peak of 150GeV gamma rays which are expected from the decay of neutralinos.

        LC

      3. so what you’re saying is this would be as effective as stringing 2 soup cans together. ok, understood. 🙂

      4. Ah but, what about “spooky action at a distance”? After all the universe began as a matter/energy singularity. Can’t get more “entangled” than that. lol

      5. – What Newton called “spooky action at a distance” for his gravitation is today’s causal field theory for interactions such as the electromagnetic field (including the linear field theory approximation to general relativity).

        – The inflationary standard cosmology did not begin in a singularity, and in fact there are theorems forbidding it in naive inflation(see Vilenkin’s et al work on past-timelike-incomplete spacetime linked to in the below link). As astrophysicist Nathan Siegel describes on what happened before big bang in the accepted cosmology:

        “But in the case of inflation (yellow), everything changes. First off, we don’t necessarily have a singularity, and we definitely don’t have one at what we traditionally think of as “the moment of the Big Bang.” Instead, we have what’s known as a past-timelike-incomplete spacetime.

        In other words, we not only don’t know whether there was a singularity at some point in the very distant, pre-inflation past, or whether inflation was truly eternal, we don’t even know whether inflation occurred for less than a yoctosecond or more than the present age of the (post-Big Bang) Universe!”

        – A single isolated quantum state is not entangled, it has to have something to be entangled with.

      6. Vilenkin’s eternal inflation is a de Sitter spacetime with a large cosmological constant. Points on the spatial subsurface in the spacetime rapidly accelerate apart. The cosmological constant ? = 8??/3 exists due to a huge quantum vacuum energy density ?. The vacuum is however not locally stable and the symmetry of that vacuum can be broken. The result is the vacuum energy can collapse to a much smaller value ?_p << ?, where ?_p means “physical vacuum.” The unbroken ? is the pure vacuum of the action or Lagrangian of fields in the universe, while ?_p is a vacuum with a more restricted symmetry not globally defined by the theory. What describes this is the inflationary field (inflaton), which in the breaking situation is described by a thermalizing term, similar to the Higgs field, which coverts a huge amount of this vacuum energy into particle-fields, radiation and matter in a local region. This is so called bubble nucleation, advanced by Coleman. The thermalizing aspects to this symmetry breaking is the high temperature of the big bang.

        In this model there is a rapidly expanding spacetime that continually produces local bubble nucleations, where our observable universe is one of these. This continues eternally with respect to the Hubble frame and time on the global de Sitter spacetime. There are though some problems or questions with this. In particular the de Sitter spacetime is approximated by an exponential function, but a pure de Sitter spacetime is really governed by a cosh(?t/3), which reaches a minimum at t = 0 and for time prior to then the spacetime is contracting. So trying to demonstrate this model really has no “start time” has been found to be difficult. The other question with this involves whether the inflaton field may dilutes with this exponential expansion where the energy in any local volume declines as E ~ |?|^2/volume, where the volume exponentially increases. So there are alternatives which say the de Sitter spacetime emerges from a supergravity vacuum where gravity decouples from other fields and becomes classical (or semi-classical) and the bubble nucleation occurs for a brief period of time as the vacuum energy of the global spacetime attenuates away. Think of a soda that is just opened, which at first produces bubbles or foam, but then goes flat.

        I tend to favor this alternative. Eternal inflation does not tell us how gravity or quantum gravity plays a role. There is then a deeper issue of how this inflationary de Sitter vacuum is established. Steinhardt considers the interaction of D-branes. I have worked similar theory http://arxiv.org/abs/1205.4710 that involves a quantum form of the Landau tri-critical point, where there is a quantum phase transition associated with the formation of a D-brane with a de Sitter vacuum. The spacetime associated with the evolution of this D-brane is this rapidly expanding de Sitter spacetime that exhibits bubble nucleations according to this quantum phase transition. However, the vacua associated with these D-branes “run out of gas,” but they are continually replenished in a QCD-like foliation.

        It must be reminded that we are talking here about dark energy and the cosmological constant. This is different in its spacetime phenomenology from dark matter. The article here on UT concerns dark matter filaments and the formation of galactic clusters and large structures.

        LC

      7. Entanglement does play a role here. Quantum fields projected into space by holography are entangled with an event horizon. The number of fields so entangled defines the entropy of the horizon. The theoretical laboratory is the black hole. With cosmology there is a similar process with the Bousso entropy bound. The relationship with a singularity, where there is some less than well understood correspondence between event horizons and singularities, is a subject of research.

        LC

  3. Another question. Does this largely end the debate as to the actual existence of dark matter? It would seem to from my novice perspective. Especially if we can observe the filaments bending light.

    1. I’m a layman, but I would think that the successful simulations of structure formation from the scale of the universe down to, at last, spiral galaxies would clinch the case. The theory is predictively better than all remaining contenders on all relevant scales. (And in the case of spiral galaxies DM has been found to be necessary to predict observations in some cases.)

      Certainly the above article with its more direct terminology re observations indicates that the area has started to come down on that side.

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