We just snapped our best photo yet of dark matter, but we still don't know just what it is. Now we might have a way to (literally) shed some light on dark matter...with an assist from super-massive black holes.


As matter falls into the super-massive black holes at the center of many galaxies, huge jets of particles are shot out of the black holes at close to the speed of light. (The creation of these particles is a bit more complicated than that, but that will do for our purposes.) These jets, which are a like a "cosmic belch" from the black hole, could collide with collections of dark matter - and that, according to Stefano Profumo of UC Santa Cruz, is when things get interesting.


We still aren't sure exactly what dark matter is (although here's an excellent primer on what we do know), but one leading theory holds that dark matter particles are the supersymmetric partners of the subatomic particles that we're more familiar with and that make up the world of regular matter. Another suggests the dark matter partially exists in a fourth spatial dimension that we can't see, an idea that is lent some support by current theoretical physics.

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Either way, Profumo says the results of a collision between dark matter and electron jets from the black hole would be pretty much identical. Unlike a lot of other possible collisions, in which the electrons would just ricochet off the other particles, here they would actually fuse with the heavier dark matter particles. This would create a dark matter electron, which would either be a supersymmetric or extra-dimensional electron, depending on which theory is correct. The energy exchange involved in making this new particle would be intense, and most of the electron's kinetic energy would be sapped in the process. This would slow the newly created dark matter electrons to a virtual standstill.

In all likelihood, the particles created would be unstable, and they would soon decay back into dark matter particles and regular electrons. But this decay process would cause the electron to emit gamma rays, which would then slowly fan out in all directions away from the clump of electrons and dark matter. Those gamma rays would be detectable from Earth, and they would be easily distinguishable from the tightly focused, fast-moving jets of particles coming from black holes.


Profumo and his team says they've already found one galaxy that might be experiencing this phenomenon. The distribution and frequencies of gamma rays emanating from the black hole at the center of the galaxy Centaurus A doesn't quite fit the orthodox predictions, and they believe this dark matter interaction effect could account for the imbalance. Another galaxy they've tested, Messier 87, doesn't fit their predicted effect, but then it's possible that, for reasons unknown, Centaurus A has a much higher concentration of dark matter than Messier 87.

[arXiv via New Scientist; image up top is of the galaxy Centaurus A.]