* Astronomy

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RE: Dark matter

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Title: Impact of dark matter on reionisation and heating
Authors: M. Mapelli (1,2), E. Ripamonti (3) ((1) SISSA, (2) University of Zürich, (3) Kapteyn Astronomical Institute, University of Groningen)

We derived the evolution of the energy deposition in the intergalactic medium (IGM) by different decaying (or annihilating) dark matter (DM) candidates. Heavy annihilating DM particles (with mass larger than a few GeV) have no influence on reionisation and heating, even if we assume that all the energy emitted by annihilations is absorbed by the IGM. In the case of lighter particles, the impact on reionisation and heating depends on the efficiency of energy absorption by the IGM. We calculated the fraction of energy produced by decays and annihilations which is effectively absorbed by the IGM. We found that this fraction is generally high at very high redshift (>>100), but drops at more recent epochs.

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Title: Determining the Nature of Dark Matter with Astrometry
Authors: Louis E. Strigari, James S. Bullock, Manoj Kaplinghat

We show that measurements of stellar proper motions in dwarf spheroidal galaxies provide a powerful probe of the nature of dark matter. Allowing for general dark matter density profiles and stellar velocity anisotropy profiles, we show that the log-slope of the dark matter profile at about twice the stellar core (King) radius can be measured to within ± 0.2 when the proper motions of 200 stars are added to standard line-of-sight velocity dispersion data. This measurement of the log-slope provides a test of Cold and Warm Dark Matter theories at a sensitivity not possible with line-of-sight velocity dispersion measurements alone. The upcoming SIM PlanetQuest will have the sensitivity to obtain the required number of proper motions in Milky Way dwarf spheroidal galaxies.

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Unfolding the Universes Dark Matter.
For the first time ever, astronomers have created a three-dimensional map showing how dark matter is distributed across the Universe. This has been achieved by an international team of scientists using data from the NASA/ESA Hubble Space Telescope.

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Dark matter gets its own dark force

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Dark Matter Candidate

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RE: Dark matter

Blobrana · L

This composite shows three different components of the COSMOS survey: The normal matter (in red) determined mainly by the European Space Agency’s XMM/Newton telescope, the dark matter (in blue) and the stars and galaxies (in grey) observed in visible light with Hubble.

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Credit: NASA, ESA and R. Massey (California Institute of Technology)

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Although 3D maps of ordinary matter have been produced before, the 3D dark matter map is a first. Watch an animation showing the dark matter map from different angles.
Because it takes light more time to travel from farther away, the more distant slices of this 3D map represent earlier eras in the history of the universe. This allowed the team to trace changes in the distribution of dark matter over a period ranging from about 6.5 billion to 3.5 billion years ago.

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Blobrana · L

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.

Three-Dimensional Distribution of Dark Matter in the Universe - 6.5 Billion Years Ago

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Credit: NASA, ESA, and R. Massey (California Institute of Technology)

The dark matter map was constructed by measuring the shapes of half a million faraway galaxies. To reach Hubble, the light of the galaxies travelled through intervening dark matter. The dark matter deflected the light slightly as it travelled 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."

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