Specifically, physicists have suggested that dark matter is composed of new kinds of particles that have very weak interactions-not just with ordinary matter but also with themselves.
Just as electromagnetism can make particles of ordinary matter attract or repel each other and emit and absorb light, so too might “Dark electromagnetism” cause similar interactions between dark matter particles and cause them to emit “Dark light” that’s invisible to ordinary matter.
Most dark matter models suggest that dark matter particles are all of one type-they either all interact with each other or they all do not.
This fraction of dark matter could influence not only the evolution of the Milky Way, but of life on Earth as well, an idea Randall explores in her latest book, Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe.
Since they likely rotate-just like the rest of the matter in their galaxies-this rotation would make these clouds of self-interacting dark matter collapse into flat disks, in much the same way as spherical clouds of ordinary matter collapsed to form the spiral disks of the Milky Way and many other galaxies.
If dark matter in large galaxies was concentrated in disks, it’s likely that at least some of the orbiting dwarf galaxies would be concentrated in flat planes because of the gravitational pull of dark matter on the dwarf galaxies, Randall and her colleagues say.
One intriguing possibility raised by interacting dark matter models is the existence of dark atoms that might have given rise to dark life, neither of which would be easily detected, Randall says.