{"id":919,"date":"2014-06-12T02:10:25","date_gmt":"2014-06-12T02:10:25","guid":{"rendered":"http:\/\/www.particlebites.com\/?p=919"},"modified":"2017-02-19T01:35:45","modified_gmt":"2017-02-19T01:35:45","slug":"black-holes-enhance-dark-matter-annihilations","status":"publish","type":"post","link":"https:\/\/www.particlebites.com\/?p=919","title":{"rendered":"Black Holes enhance Dark Matter Annihilations"},"content":{"rendered":"
\n \tTitle:<\/strong> Effect of Black Holes in Local Dwarf Spheroidal Galaxies on Gamma-Ray Constraints on Dark Matter Annihilation<\/ br>
\n \tAuthor:<\/strong>\u00a0Alma X. Gonzalez-Morales, Stefano Profumo, Farinaldo S. Queiroz<\/ br>
\n \tPublished<\/strong>:\u00a0arXiv:1406.2424<\/a> [astro-ph.HE]<\/ br>\n<\/div>\n
\"Upper<\/a>
Upper bounds on dark matter annihilation from a combined analysis of 15 dwarf spheroidal galaxies for NFW (red) and Burkert (blue) DM density profiles. Fig. 4 from arXiv:1406.2424<\/a>.<\/figcaption><\/figure>\n

In a previous\u00a0ParticleBite<\/a> we showed how\u00a0dwarf spheroidal galaxies\u00a0can tell us about dark matter interactions. As a short summary, these are dark matter-rich “satellite [sub-]galaxies” of the Milky Way that are ideal places to look for photons coming from dark matter annihilation into Standard Model particles.\u00a0In this post we highlight a recent update to that analysis.<\/p>\n

The rate at which a pair of dark matter particles annihilate in\u00a0a galaxy is proportional to\u00a0the square of the dark matter\u00a0density. The authors point out that if the dwarf spheroidal galaxies contain intermediate mass black holes ($latex \\sim 10^4$ times the mass of the sun), then its possible that the\u00a0dark matter in the\u00a0dwarf is\u00a0more densely packed\u00a0near the black hole.\u00a0The authors redo the\u00a0FERMI analysis for DM annihilation in\u00a0dwarf spheroidals with 4 years of data (see our\u00a0previous\u00a0ParticleBite<\/a>) with the assumption that\u00a0these dwarfs contain a black hole consistent with their observed properties.<\/p>\n

While the dwarf galaxies\u00a0have little stellar content,\u00a0one can use the visible stars to measure the stellar velocity dispersion, $latex \\sigma_*$.\u00a0As a benchmark, the authors use the Tremaine relation to determine\u00a0the black hole mass as a function of the\u00a0observed\u00a0velocity dispersion,<\/p>\n

\"Screen<\/a><\/p>\n

Here $latex M_{\\odot}$ is the mass of the sun. Given this mass and its effect on the dark matter density, they can then calculate the\u00a0J\u00a0<\/em>factor that encodes the `astrophysical’ line of slight integral of the squared dark matter density\u00a0to\u00a0observers on the Earth.\u00a0Following the FERMI analysis,\u00a0authors then set bounds on the dark matter\u00a0annihilation cross section as a function of the dark matter mass for 15 dwarf spheroidals:<\/p>\n

\"DM<\/a>
DM annihilation cross-section constraints for annihilation into a pair of b quarks, from 1406.2424 Fig. 1. The shaded band is the target cross section\u00a0to obtain the correct dark matter relic density\u00a0through thermal freeze out, the red box is the target cross section for a dark\u00a0matter interpretation of\u00a0an excess in gamma rays in the galactic center.<\/figcaption><\/figure>\n

Observe that the bounds are significantly stronger than those in the\u00a0original FERMI analysis. In particular,\u00a0the strongest bounds\u00a0thoroughly rule out the “40 GeV DM annihilating into a pair of b quarks” interpretation of a reported excess in gamma rays coming from the galactic center. These\u00a0bounds, however, come with several caveats that are\u00a0described in the paper. The\u00a0largest caveat is that\u00a0the existence of a black hole in any of these systems is only assumed. The authors\u00a0note that numerical simulations suggest that\u00a0there\u00a0should be black holes in these systems, but to date there has been no verification of their existence.<\/p>\n

Further Reading<\/strong><\/p>\n