Kilohertz quasi-periodic oscillations and strong field gravity in X-ray   binaries
  In the past five years observations with the Rossi X-ray Timing Explorer have revealed fast quasi-periodic oscillations in the X-ray flux of about 20 X-ray binaries. Thought to originate close to the surface of a neutron star, these oscillations provide unique information about the strong gravitational field in which they are produced. 
Mariano Mendez (SRON)