Usually we think of black holes pulling things in rather than hurling them out, but C Chicone and B Mashhoon of the University of Missouri would argue differently. While radially moving particles do get pulled towards the black hole, it turns out that our intuition is not so good when it comes to swarms of ultrarelativistic particles moving tangentially to it.
Tidal forces, the researchers argue, can accelerate the particles to almost the speed of light. The interactions of the charged particles with the ambient medium can then lead to the transfer of this tidal energy to particles in the ambient medium. These can escape from the system to appear far away as ultra-high-energy cosmic rays.
Chicone and Mashhoon say that this acceleration mechanism agrees with observations by the Chandra X-ray Observatory of accelerated motion normal to the radial jets in four neutron stars in our galaxy: the Crab Pulsar, the Vela Pulsar, PSR B1509-58 and SNR G54.1+0.3. The mechanism may also account for ultra-high-energy cosmic rays with energies above the Greisen-Kuzmin-Zatsepin cut-off for extra-galactic sources of 1020 eV. Microquasars or neutron stars in our galaxy could be sources of the highest-energy cosmic rays - an idea that the Pierre Auger Observatory may help to shed light on in the near future.
Further reading
C Chicone and B Mashhoon 2005 http://arxiv.org/abs/astro-ph/0502560