ESA Science & Technology - Illustration of 4U 0614+091 (annotated)

This illustration of 4U 0614+091 depicts the accretion disc around the neutron star, with material flowing onto it from the white dwarf companion, and symmetrical jets of relativistic matter ejected perpendicular to both sides of the disc.

X-ray photons irradiating the disc are reflected by the material within it. As the gas in the disc contains a wealth of hot electrons, photons scattering off these electrons gain energy, resulting in a broadening of the spectral lines towards higher energies. Gravitational redshift and the relativistic Doppler effect broaden the spectral lines towards lower energies - a signature of the strong gravitational field of the neutron star.