Supposing a distant active black hole is vomiting towards you, what will you see?

Recently, a research group led by Prof. WANG Zhongxiang from Shanghai Astronomical Observatory discovered a month-long Quasi-Periodic Oscillation (QPO) from such a black hole. This is the only QPO in gamma ray ever found by the Fermi Gamma-ray Space Telescope. This work has been published in Nature Communications recently.

For most large galaxies, a gigantic black hole sit at the very center. When they are munching on gas and stars, they are in the active state. Approximately 10% of AGN are found to have a jet, launched from the immediate vicinity of the SMBHs. When such a jet happens to be pointing close to the line of sight, the light from the jet will dominate. Such AGNs are classified as blazars.

Multi-wavelength monitoring observations of AGNs have revealed one type of peculiar phenomenon called the Quasi-Periodic Oscillations (QPOs); i.e., at some wavelengths the AGN brightens and dims periodically.

QPOs with timescales of years may indicate that there is a binary black hole system in the center. QPOs with timescales of days may indicate that the phenomenon happening around the innermost stable orbit of a black hole.

Recently, based on the gamma-ray data obtained with the Fermi Gamma-ray Space Telescope, one research group at SHAO led by Prof. WANG Zhongxiang have found a 34.5 day QPO in emission from a blazar named PKS 2247-131, 3.6 billion light-years away from the Earth.

“This blazar started to have a bright gamma-ray flare since 2016 October. After its flaring flux peak, a 34.5 day periodic modulation is clearly seen in its light curve.” Said the first author Dr. ZHOU Jia-Neng.