Mapping the Cosmic Web

Astronomers theorize that the early universe was very smooth, and that the distribution of matter was uniform with tiny variations in density that grew into a web-like pattern. These areas of slightly higher density also had slightly more gravity to attract more matter. Over time, the universe evolved into a web of filaments and vast sheets, largely made of dark matter, which form the structure of the universe today.

Galaxy Cluster MACS J0717 Dark Matter Map
NASA, ESA, Harald Ebeling (University of Hawaii at Manoa) & Jean-Paul Kneib (LAM)
This cosmic web forms the large-scale backbone of the universe. Hubble’s high resolution can make detailed observations that spot minute distortions in how light from distant objects bends around a foreground galaxy cluster. Such observations allowed astronomers to make the first map of a filament funneling matter into the massive galaxy cluster MACS J0717. The astronomers expanded Hubble’s two-dimensional observations by using data from other observatories that measured distances to the galaxies in the filament.
Multiwavelength View of MACS J0717
NASA, ESA, CXC, C. Ma, H. Ebeling and E. Barrett (University of Hawaii/IfA), et al. and STScI
Hubble observations of MACS J0717 and its filament also revealed the first documented collision of four separate galaxy clusters. The collisions are the result of the 13-million-light-year-long filament of normal and dark matter streaming into a region already full of matter.
This composite image of visible light data from Hubble and x-ray data from NASA’s Chandra X-ray Observatory reveals the hot gas (blue) and cooler gas (reddish-purple). Astronomers can estimate the speed and direction of each cluster's motion — perpendicular to the line of sight — by studying the difference between the average position of the galaxies and the peak in the hot gas. As the filament funnels matter into the cluster, collisions between the gas in two or more clusters causes the hot gas to slow down, dissipating some of its kinetic energy as heat. But the massive and compact galaxies do not slow down as much as the gas does, so they move ahead of it. This allows the researchers to three-dimensionally map the geometry and motion in the system, thereby mapping the large-scale structure of the region located some 5.4 billion light-years from Earth.
3-D Distribution of Dark Matter
NASA, ESA, and R. Massey (California Institute of Technology)
Nearly 1,000 hours of Hubble observations similarly enabled an international team of 70 astronomers to create the first three-dimensional map of the web-like, large-scale distribution of dark matter. The map is comprised of 575 slightly overlapping Hubble images that stretch halfway back in time to the beginning of the universe. They reveal a loose network of dark matter filaments, gradually collapsing and growing clumpier over time under the relentless pull of gravity, confirming theories of how structure formed in our evolving universe.
Each slice reveals the changing distribution of dark matter in a discrete epoch of time. Astronomers calibrated each epoch by measuring the cosmological redshift of the lensing galaxies used to map the dark matter’s distribution, placing them into different time/distance "slices."
3-D Distribution of Dark Matter
NASA, ESA, and R. Massey (California Institute of Technology)
Astronomers combined the slices to create the three-dimensional map of dark matter over time. The three axes of the box correspond to sky position (right ascension and declination), and distance from Earth increasing from left to right (as measured by cosmological redshift). Note how the dark matter clumping becomes more pronounced, moving right to left across the map, from the early universe to the more recent universe, confirming theories of how the large-scale structure of the universe formed and evolved.
Cosmic Web and Slime Mold
NASA, ESA, and J. Burchett and O. Elek (UC Santa Cruz)
Recently, simple single-cell organisms that feed on dead plant material became the analogous counterpart to how the large-scale structure of the universe formed. Researchers developed an algorithm that mimics the brainless slime mold’s efficiency at building complex filaments to capture new food. They then applied the algorithm to data containing the locations of 37,000 galaxies mapped by the Sloan Digital Sky Survey. The galaxies are analogous to the slime mold’s food. The algorithm revealed the striking similarity between how the slime mold builds complex filaments to capture new food, and how gravity constructs the cosmic web filaments between galaxies and galaxy clusters.
After the three-dimensional computer model estimated the location of the cosmic filaments, the astronomers used archival Hubble observations to detect and study the gas permeating the web at points along those predicted filaments. They examined the ultraviolet light from 350 distant quasars in the Hubble Spectroscopic Legacy Archive. Because these quasars are so far from the galaxies, the researchers were able to use the Hubble data to look for the telltale absorption of undetected hydrogen gas in the spectroscopic signature of the quasars and link the gas to the universe's large-scale structure.
The three sets of paired inset images represent galaxies with yellow dots (left). Next to each galaxy snapshot is an image of the galaxies with the cosmic web's connecting strands in purple (right) superimposed on them.

This visualization of a computer simulation showcases the ‘cosmic web’, the large scale structure of the universe. Each bright knot is an entire galaxy, while the purple filaments show where material exists between the galaxies. To the human eye, only the galaxies would be visible, and this visualization allows us to see the strands of material connecting the galaxies and forming the cosmic web. This visualization is based on a scientific simulation of the growth of structure in the universe. The matter, dark matter, and dark energy in a region of the universe are followed from very early times of the universe through to the present day using the equations of gravity, hydrodynamics, and cosmology. The normal matter has been clipped to show only the densest regions, which are the galaxies, and is shown in white. The dark matter is shown in purple. The size of the simulation is a cube with a side length of 134 megaparsecs (437 million light-years). The camera choreography is a straight line path through the simulation. The camera accelerates from a standstill at the start, flies at a constant speed, and then decelerates to a stop at the end. The “cruising speed” of the camera is 250,000 parsecs per frame, or about 20 million light-years per second (at 24 frames per second). That’s more than 600 trillion times the speed of light. Buckle your seatbelts. The simulation is periodic, and the camera flies through it several times. A skew angle is used to avoid showing the same structures on each fly through. The camera path (after accelerating to full speed) does repeat every 2,000 frames. Hence, one can get an infinite loop by showing the frames 100 - 2099 over and over.

Visualization: Frank Summers (STScI); Simulation: Martin White and Lars Hernquist, Harvard University

Learn More

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MACS J0717 with Mass Overlay
This enormous image shows Hubble’s view of massive galaxy cluster MACS J0717.5+3745. The large field of view is a combination of 18 separate Hubble images.
Galaxy Cluster MACS J0717
Using data from NASA's Chandra X-ray Observatory, Hubble Space Telescope, and the Keck Observatory in Hawaii, astronomers determined the three-dimensional geometry and motion in the system MACS J0717.5+3745 (or MACS J0717, for short), located about 5.4 billion light-years from Earth.
Hubble Maps the Cosmic Web of "Clumpy" Dark Matter in 3-D
An international team of astronomers using NASA's Hubble Space Telescope has created a three-dimensional map that provides the first direct look at the large-scale distribution of dark matter in the universe.
Slime Mold Simulations Used to Map Dark Matter Holding Universe Together
The behavior of one of nature's humblest creatures is helping astronomers probe the largest structures in the universe.