Astronomy. A journey through time.
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Biomedical subjects
Joseph Silk
Publications and source records attributed to Joseph Silk.
Dark minihalos with intermediate mass black holes.
We argue that the Milky Way (MW) contains 10(3)-10(4) intermediate mass black holes (IMBHs) of mass approximately 10(2-3)M. Some IMBHs are naked, and some are enshrouded by dense dark minispikes and by minihalos of (10(6)-10(7))M circle. The IMBH is formed off-center by gas accretion in a minihalo. These dense minihalos (the nearest at about 2 kpc) survive mostly without tidal stripping by the MW, and are largely invisible except that their pointlike neutralino annihilation signals (with bolometric luminosities of 10(3-5)L circle 50 GeV / mChi within 0.01-0.1 pc of their centers) stand out well above the MW background and are more luminous than outer dwarf satellite galaxies.
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Possible evidence for MeV dark matter in dwarf spheroidals.
The observed 511 keV emission from the galactic bulge could be due to very light (MeV) annihilating dark matter particles. To distinguish this hypothesis from conventional astrophysical sources, we study dwarf spheroidals in the region observed by the International Gamma-Ray Astrophysics Laboratory/SPI such as Sagittarius. As these galaxies have comparatively few stars, the prospects for 511 keV emission from standard astrophysical scenarios are minimal. The dwarf spheroidals do, however, contain copious amounts of dark matter. The observation of 511 keV emission from Sagittarius should be a "smoking gun" for MeV dark matter.
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MeV dark matter: has it been detected?
We discuss the possibility that the recent detection of 511 keV gamma rays from the galactic bulge, as observed by INTEGRAL, is a consequence of low mass (1-100 MeV) particle dark matter annihilations. We discuss the type of halo profile favored by the observations as well as the size of the annihilation cross section needed to account for the signal. We find that such a scenario is consistent with the observed dark matter relic density and other constraints from astrophysics and particle physics.
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Solar neutrinos: probing the quasi-isothermal solar core produced by supersymmetric dark matter particles.
SNO measurements strongly constrain the central temperature of the Sun, to within a precision of much less than 1%. This result can be used to probe the parameter space of supersymmetric dark matter. In this first analysis we find a lower limit for the weakly interacting massive particle (WIMP) mass of 60 GeV. Furthermore, in the event that WIMPs create a quasi-isothermal core, they will produce a peculiar distribution of the solar neutrino fluxes measured on Earth. Typically, a WIMP with a mass of 100 GeV and annihilation cross section of 10(-34) cm(3)/sec will decrease the neutrino predictions, by up to 4% for the Cl, by 3% for the heavy water, and by 1% for the Ga detectors.
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