  X-ray flares have been discovered in black hole systems, such as gamma-ray
bursts, the tidal disruption event Swift J1644+57, the supermassive black hole
Sagittarius A$^*$ at the center of our Galaxy, and some active galactic nuclei.
Their occurrences are always companied by relativistic jets. However, it is
still unknown whether there is a physical analogy among such X-ray flares
produced in black hole systems spanning nine orders of magnitude in mass. Here
we report the observed data of X-ray flares, and show that they have three
statistical properties similar to solar flares, including power-law
distributions of energies, durations, and waiting times, which both can be
explained by a fractal-diffusive self-organized criticality model. These
statistical similarities, together with the fact that solar flares are
triggered by a magnetic reconnection process, suggest that all of the X-ray
flares are consistent with magnetic reconnection events, implying that their
concomitant relativistic jets may be magnetically dominated.
