A Fundamental Test of the Nature of Dark Matter

Dark matter may consist of weakly interacting elementary particles or of macroscopic compact objects. We show that the statistics of the gravitational lensing of high-redshift supernovae strongly discriminate between these two classes of dark matter candidates. We develop a method of calculating the magnification distribution of supernovae, which can be interpreted in terms of the properties of the lensing objects. With simulated data, we show that ≳50 well-measured Type Ia supernovae (Δm ∼ 0.2 mag) at redshifts ∼1 can clearly distinguish macroscopic from microscopic dark matter if Ω0 ≳ 0.2 and all dark matter is in one form or the other.