* Astronomy

Blobrana · L

RE: Dark matter

Blobrana · L

The mysterious dark matter that makes up most of the material in the universe may actually have an electric charge, a new study suggests. If so, it might help explain why astronomers see so few dwarf galaxies in orbit around larger ones.
Dark matter is detected by its tug on light and visible matter, so astrophysicists have largely assumed that it interacts mostly through the force of gravity and not electromagnetism, for example. Indeed, the leading dark matter candidates, known as weakly interacting massive particles, or WIMPs, are electrically neutral.
But theorists Leonid Chuzhoy and Rocky Kolb of the University of Chicago say it may be time to consider the possibility that dark matter is actually composed of charged massive particles, or CHAMPs. That would mean magnetic fields could push on or deflect dark matter adding another way for it to interact with the known universe.

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Blobrana · L

Title: A Search for Z=-1 Dark Matter Annihilation Products in Cosmic Rays with AMS-01
Authors: Gray Rybka

The majority of mass in the universe has not been observed optically and is termed dark matter. The supersymmetric neutralino provides an interesting dark matter candidate, which may self-annihilate in our galaxy, producing particles visible in the cosmic ray spectrum. During a ten day space shuttle flight, the AMS-01 detector recorded over 100 million cosmic ray events. This analysis searches for the products of neutralino annihilation in the AMS-01 Z=-1 spectrum, and uses the results to place limits on which supersymmetric and dark matter halo distribution models are compatible.

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Blobrana · L

Title: Placing direct limits on the mass of earth-bound dark matter
Authors: Stephen L. Adler
(Version v4)

We point out that by comparing the total mass (in gravitational units) of the earth-moon system, as determined by lunar laser ranging, with the sum of the lunar mass as independently determined by its gravitational action on satellites or asteroids, and the earth mass, as determined by the LAGEOS geodetic survey satellite, one can get a direct measure of the mass of earth-bound dark matter lying between the radius of the moon's orbit and the geodetic satellite orbit. Current data show that the mass of such earth-bound dark matter must be less than 4 x 10^{-9} of the earth's mass.

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Blobrana · L

Title: A lower bound on the mass of Dark Matter particles
Authors: Alexey Boyarsky, Oleg Ruchayskiy, Dmytro Iakubovskyi

We discuss the bounds on the mass of Dark Matter (DM) particles, coming from the analysis of DM phase-space distribution in dwarf spheroidal galaxies (dSph's). After reviewing existing approaches, we choose two methods to derive such a bound. The first method depends on the information about the current phase space distribution of DM particles only, while the second one uses both the initial and final distributions. We discuss the recent data on dSph's as well as astronomical uncertainties in relevant parameters. As an application, we present lower bounds on the mass of DM particles, coming from various dSph's, using both methods. The model-independent bound holds for any type of fermionic DM. Stronger, model-dependent bounds are quoted for several DM models (thermal relics, non-resonantly and resonantly produced sterile neutrinos, etc.). The latter bounds rely on the assumption that baryonic feedback cannot significantly increase the maximum of a distribution function of DM particles. Combining these results with the X-ray bounds of DM decay lines, we conclude that the scenario when DM is made of sterile neutrinos produced via non-resonant oscillations with the active neutrinos, is disfavoured. The results of this work allow to reach this conclusion without relying on the Lyman-alpha analysis. The model of DM sterile neutrinos resonantly produced in the presence of lepton asymmetry remains viable. Within minimal neutrino extension of the Standard Model (the nuMSM) both mass and the mixing angle of the DM sterile neutrino are bounded from above and below, which suggests a possibility for its experimental search.

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Blobrana · L

Title: Planet-bound dark matter and the internal heat of Uranus, Neptune, and hot-Jupiter exoplanets
Authors: Stephen L. Adler

We suggest that efficient accretion of planet-bound non-self-annihilating dark matter by the Jovian planets, and by hot-Jupiter exoplanets, could be a significant source of their internal heat. The anomalously low internal heat of Uranus would then be explained if the collision believed to have tilted the axis of Uranus also knocked it free of most of its associated dark matter cloud.

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Blobrana · L

Title: Mirror dark matter discovered?
Authors: Z.K. Silagadze
(Version v2)

Recent astrophysical data indicates that dark matter shows a controversial behaviour in galaxy cluster collisions. In case of the notorious Bullet cluster, dark matter component of the cluster behaves like a collisionless system. However, its behaviour in the Abell 520 cluster indicates a significant self-interaction cross-section. It is hard for the WIMP based dark matter models to reconcile such a diverse behaviour. Mirror dark matter models, on the contrary, are more flexible and for them diverse behaviour of the dark matter is a natural expectation.

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Blobrana · L

A new study shows that large-scale voids are empty of massive dark matter halos as well as luminous galaxies.

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Blobrana · L

Rumours are swirling that a European satellite mission may have detected dark matter, the mysterious particles thought to make up as much of 85% of all matter in the Universe.
Nature has learned that the PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) mission a collaboration between Italy, Russia, Germany and Sweden has detected a surplus of high-energy antielectrons whizzing through space. The antielectrons, also called positrons, could be the clearest signature yet of the dark matter lurking in the Milky Way, according to Dan Hooper, a theoretical physicist at Fermilab in Batavia, Illinois.

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Blobrana · L

Title: Placing direct limits on the mass of earth-bound dark matter
Authors: Stephen L. Adler

We point out that by comparing the total mass (in gravitational units) of the earth-moon system, as determined by lunar laser ranging, with the sum of the lunar mass as independently determined by its gravitational action on satellites or asteroids, and the earth mass, as determined by the LAGEOS geodetic survey satellite, one can get a direct measure of the mass of earth-bound dark matter lying between the radius of the moon's orbit and the geodetic satellite orbit. Current data show that the mass of such earth-bound dark matter must be less than 4 x 10^{-9} of the earth's mass.

Read more (5kb, PDF)