Anti matter seems to be fairly well understood. We see it in cosmic ray collisions with particles in the upper atmosphere. We use it in PET scans in hospitals. We create it in the Large Hadron Collider to smash into ordinary matter and investigate the inner workings of both.
Antimatter is known to have the opposite electric charge and other properties to its ordinary matter equivalent. We know there’s more matter than antimatter, but don’t know why. But while we can investigate strong forces like electromagnetism, another mystery arises when considering a very weak force – gravity.
In most of the situations we see antimatter, it is zipping along at a great speed and its momentum is hardly affected by accelerations due to gravity. In most cases the deflection due to magnetic fields is too great for gravitational effects to be measured in the short life of the stuff. To put it bluntly, we’ve never really just let antimatter go and seen whether it goes up, down or stays put.
Virtual particles and antiparticles are constantly being created and destroyed in pairs. Hawking suggested that should this happen on the boundary of a black hole, the gravity should be sufficient to rip out one of the pair before it is attracted to its antiparticle and they annihilate. As such particle radiation would be detectable. Now other researchers have suggested that if antimatter does interact with mass differently to ordinary matter, the signature will be heavy in anti matter.
Their specific example was the creation and destruction of neutrinos, which are affected only by gravity. Close enough to a black hole and the matter one would be pulled in while the antimatter one, if the hypothesis is right, should be pushed out. The IceCube Neutrino observatory should be able to spot black holes shining bright in antineutrinos. However, there are other hypotheses that can produce such a signal, so even if the detectors did see such an event, they would need further work to determine if antimatter really does run away from mass.