Astronomers have taken their first 3D look at a gigantic filament of dark matter, an invisible cosmic structure that can only be recognized by its gravitational effects on the environment.
The universe is believed to be structured like a jumble, with long chains of mostly dark matter intersecting at huge clusters of galaxies. Because dark matter cannot be seen directly, these filaments are difficult to see. However, with the Hubble Space Telescope, astronomers have succeeded in studying one of the elusive cosmic strands in 3D.
The researchers searched for a 60 million light-year long strand of dark matter around the massive galaxy cluster MACS J0717. The galaxy cluster is one of the largest seen to date, located about 5.4 billion light years from Earth.
“From our previous work on MACS J0717, we knew that this cluster is actively growing, making it a key target for a detailed study of the cosmic web,” said study researcher Harald Ebeling of the University of Hawaii at Manoa in a statement Tuesday October 16 ). [Hubble’s Dark Matter Strand View in 3D (Video)]
Ebeling and his colleagues analyzed images of the cluster from the Hubble Space Telescope as well as the Japanese Subaru telescope and the Canada-France-Hawaii telescope. They also used gravitational lens techniques to map the expansion of the massive filament of dark matter.
(Photo credit: NASA, ESA, Harald Ebeling (University of Hawaii at Manoa) and Jean-Paul Kneib (LAM))
Albert Einstein’s general theory of relativity holds that massive objects, including dark matter, warp space, and time around them, cause light passing through them to move on a crooked path. Filaments thus distort the images of galaxies in the background and the researchers were able to convert the image distortions into a mass map for the chain of dark matter that extends from MACS J0717.
Additional observations from ground-based telescopes enabled astronomers to map the structure of the filament in 3D, a first for astronomers. (Researchers say the first identification of a section of dark matter filament was made between the two galaxy clusters Abell 222 and Abell 223 earlier this year.)
The team found that the filament from the core of the MACS J0717 extends back almost along our line of sight from Earth.
At 60 million light years in length, the filament’s sheer size is extreme, researchers said. If representative of other strands, those strings could contain even more dark matter than theorists predicted.
The study is published in the November 1st issue of the Royal Astronomical Society’s Monthly Notices.
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