Can you tell me? Just kidding! The real answer is: we don’t know. Finding out the identity of dark matter is the major overarching theme of my research.
What do we know about dark matter?
We know how much of it there is, to pretty high precision. Dark matter eats up almost exactly one-quarter of the mass-energy budget of the Universe. It isn’t distributed uniformly, though, but clumps into “clouds” that physicists call “halos”. These halos are the birthplaces of galaxies — without the gravity provided by halos, gas (4% of the Universe’s mass-energy budget) cannot settle and cool enough to form stars on the timescales we know they must. It’s like the frosting holding the sprinkles onto the cupcake. Today, halos and galaxies don’t grow as fast as they once did, because of the mysterious gravitational repulsion from “dark energy” (70% of the cosmic mass-energy budget).
How do we learn more about dark matter?
There are two types of method to learn about dark matter. First, there are laboratory-based searches, where we either make dark matter or detect it via its interaction with us. Second, we can use astronomy to determine how dark matter affects the distribution and motion of luminous matter. My group uses both approaches, through a combination of theory and observation, although we are increasingly focusing on the astronomical approach. I’ve stretched the limits of my illustration skill to make these cartoons to illustrate detection.
Laboratory-based approaches:
Astronomical approach [main focus of my group]:
