Using the Hard X-ray Modulation Telescope (HXMT), astronomers from Shanghai Astronomical Observatory in China have detected a low frequency, quasi-periodic oscillation in a black hole high mass X-ray binary known as Cygnus X-1. The finding is reported in a paper published April 29 on arXiv.org.
X-ray binaries consist of a normal star or a white dwarf transferring mass onto a compact neutron star or a black hole. Based on the mass of the companion star, astronomers divide them into low-mass X-ray binaries (LMXBs) and high-mass X-ray binaries (HMXBs).
X-ray binaries may exhibit X-ray variability in the form of relatively sharp quasi-periodic oscillations (QPOs) with millihertz (mHz) to kilohertz (kHz) frequencies. Researchers believe that QPOs occur when X-rays are emitted near the inner edge of an accretion disk in which gas swirls onto a compact object like a neutron star or a black hole. Generally, QPOs are divided into type-A, -B, and -C, according to their frequency, amplitude and coherence.
