Hubble Maps the Cosmic Web of “Clumpy” Dark Matter in 3-D

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 the first three-dimensional map of the large-scale distribution of dark matter in the universe. Dark matter is an invisible form of matter whose total mass in the universe is more than five times that of “normal” matter (i.e., atoms). The nature of dark matter is still unknown. Its presence in the universe is inferred from its current influence within galaxies and clusters of galaxies, and the gravitational effect it has had on the evolution of structure in the universe. The first direct detection of dark matter was made this past year through observations of the Bullet Cluster of galaxies.

This new map provides the best evidence to date that normal matter, largely in the form of galaxies, accumulates along the densest concentrations of dark matter. The map reveals a loose network of filaments that grew over time and intersect in massive structures at the locations of clusters of galaxies. The map stretches halfway back to the beginning of the universe and shows how dark matter has grown increasingly “clumpy” as it collapses under gravity.

The dark matter map was constructed by measuring the shapes of half a million faraway galaxies. To reach Hubble, the light of the galaxies traveled through intervening dark matter. The dark matter deflected the light slightly as it traveled through space. Researchers used the observed, subtle distortion of the galaxies’ shapes to reconstruct the distribution of intervening mass along Hubble’s line of sight, a method called “weak gravitational lensing.”

For astronomers, the challenge of mapping dark matter in the universe has been similar to mapping a city from nighttime aerial snapshots showing only streetlights. Dark matter is invisible, so only the luminous galaxies can be seen directly. These new map images are equivalent to seeing a city, its suburbs and country roads in daylight for the first time. Major arteries and intersections become evident, and a variety of neighborhoods are visible.

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