An international team of astrophysicists have discovered a giant string of invisible dark matter joining together two clusters of galaxies - Abell 222 and Abell 223 - turning a scientific theory into an observed fact. The filaments are considered to be the "glue" that binds huge galaxy clusters together, but dark matter is very difficult to detect because it does not emit any radiation.
Dark matter cannot be seen, but can be sensed through its gravitational pull. According to Space.com, dark matter is thought to make up as much as 80 percent of all matter in the universe. Astrophysicists managed to detect this string of invisible dark matter due to the gravitational ripples it caused in space, distorting the light from nearby stars. The filament connects the Abell 222 and Abell 223 galaxy clusters about 2.7 million light-years away from Earth. The discovery was published online Wednesday, July 4, in the journal Nature.
"This is the first time [a dark matter filament] has been convincingly detected from its gravitational lensing effect," said Jörg Dietrich of the University Observatory Munich in Germany. "It is a resounding confirmation people didn't think was possible at this point."
"Soon after the Big Bang, regions that were slightly denser than others pulled in dark matter, which clumped together and eventually collapsed into flat 'pancakes,' explains the article published in the journal Nature. "Where these pancakes intersect, you get long strands of dark matter, or filaments," the publication quoted Dietrich. "clusters of galaxies then formed at the nodes of the cosmic web, where these filaments crossed."
Detecting filaments had previously been considered impossible with current technology, but astronomers could pick out a signal due to the geometry of the two galaxies here, angled away from Earth. Using telescope data from Mauna Kea on Hawaii to analyze the light from 40,000 galaxies behing Abell 222 and Abell 223, astronomers found a tell-tale distortion in space-time. This distortion shows a filament of dark matter connecting the two clutters. This is a major discovery, as until now most of what is known about dark matter was based on computer simulations.
"The standard wisdom is that the gravitational lensing of filaments is too weak to be detected with current telescopes," Dietrich told Space.com. "Only when we realized this system has such a peculiar geometry did we realize we have a chance."
"The data was observed in 2001 and just had been sitting in the archive and no one ever used it," added Dietrich. "It took a while for us to realize that this data is around."
