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Extragalactic dark matter

Dark matter particles can interact with each other, albeit very weakly.  In regions of high density, such as at the centers of galaxies, dark matter particles can annihilate to produce high-energy photons that may be detectable.  This image shows what the sky would like if it were lit up by such a dark matter signal---the pattern traces thousands of galaxies beyond the Milky Way.  The Fermi Large Area Telescope is currently one of the most powerful probes for such dark matter signals.  Using this publicly available data, we have searched for dark matter in many hundreds of galaxy groups.

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galactic dark matter

We have also studied gamma rays produced within the Milky Way galaxy and found evidence for a new population of sources near the Galactic Center.  These unresolved sources can explain an excess of high-energy photons that were previously attributed to dark matter.  This analysis harnesses basic ideas from image processing to distinguish photons that are 'clumpy' rather than smoothly distributed in the sky.  One possibility is that these sources are millisecond pulsars that were dragged to the heart of our Galaxy as it formed.  

[In the Press]