Astronomers using the Hubble telescope have managed to study a giant, 60 million light-year dark matter filament in a distant galaxy cluster MACS J0717. If the mass measured is accurate, then it could account for where a lot of the “missing mass” of dark matter has gone.
The theory of the Big Bang predicts that variations in the density of matter in the very first moments of the Universe led the bulk of the matter in the cosmos to condense into a web of tangled filaments. This view is supported by computer simulations of cosmic evolution, which suggest that the Universe is structured like a web, with long filaments that connect to each other at the locations of massive galaxy clusters. However, these filaments, although vast, are made mainly of dark matter, which is incredibly difficult to observe – because it is, well, dark (not emitting or absorbing light or other radiation to make it detectable).
To get an idea of just how vast this filament is (60 million light years), our own galaxy is about 140,000 light years across and the nearest galaxy to us, Andromeda, is 2.5 million light years away.
This filament study is actually composited from observations from a great many sources, all of which add to the process to be able to generate a 3-dimensional study of the filament. High resolution images from Hubble, Subaru and CFH telescopes were combined with spectroscopic data on the movement of galaxies within it from the Keck and Gemini observatories.
The image at the top of this article is a composite image of both the optical image obtained by data from Hubble, and a mass map obtained by carefully observing the amount of gravitational lensing of the light from galaxies by the filament itself.
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. So much that more than half of all the mass in the Universe may be hidden in these structures.
This article summarised from materials provided by the ESA.
The research is presented in a paper entitled “A Weak-Lensing Mass Reconstruction of the Large-Scale Filament Feeding the Massive Galaxy Cluster MACSJ0717.5+3745” – (Mathilde Jauzac, Eric Jullio, Jean-Paul Kneib, Harald Ebeling, Alexie Leauthaud, Cheng-Jiun Ma, Marceau Limousin, Richard Massey and Johan Richard) to be published in the 1 November 2012 issue of Monthly Notices of the Royal Astronomical Society. A web based copy is provided here.