"when ordinary matter meets anti-matter, it's an Angels and Demons style explosion" Oh goodness me, no. They annihilate to create a lepton pair. There is no ex

"when ordinary matter meets anti-matter, it's an Angels and Demons style explosion" Oh goodness me, no. They annihilate to create a lepton pair. There is no explosion, really. Subatomic physics is much more boring than popular science would have you believe! You must try quite hard to get an explosion - it isn't chemistry, where things explode simply because it's Wednesday. Particles that are their own antimatter are not all that exotic either. Z bosons, gluons and photons are all their own antiparticles too, and perhaps neutrinos. As I understand it (and I am a nuclear physicist, not an astrophysicist) there are few (no?) observed natural interactions known to produce high energy positrons (i.e. with energy >1 GeV). So, if you find one coming from space, it is an indicator that something unexplained has happened. Since we know where there must be clusters of dark matter and WIMPs are theorised to produce such positrons, dark matter decay is the leading candidate for an explanation for a high energy positron coming from such a direction. Or it could be aliens, of course.