Recently, the research team of the Observation High Energy Astrophysics Group of the Shanghai Astronomical Observatory of the Chinese Academy of Sciences used a hard X-ray modulation telescope satellite ("Wise Eye Satellite") to detect a high-energy quasi-periodic oscillation signal of 88mHz when the soft spectrum of the famous black hole binary star Cygnus X1, and the research work has been published in the Astrophysical Journal.
The famous black hole X-ray binary system , Cygnus X1 , was one of the earliest X-ray sources discovered in the 1960s , consisting of a massive O-type star and a black hole , which orbited each other , and the stellar wind material was accretized by the black hole and continuously radiated strong X-rays from the black hole , making it one of the few known black hole X-ray binary stars. The latest measurements show that it is about 7200 light-years from Earth, and the black hole in the binary system has a mass of about 21 times the mass of the Sun, making it the most massive stellar-level black hole in the Milky Way and the only known black hole in the Milky Way with massive X-ray binary.
"Huiyan Satellite" is China's first space X-ray astronomical satellite, covering an energy range of 1--250 keV, is a space X-ray astronomical telescope that can not only achieve wide-band, large-field X-ray survey, but also a space X-ray astronomical telescope that can study high-energy objects such as black holes and neutron stars, and a space X-ray astronomical telescope with high sensitivity. The day after liftoff, the "Wise Eye Satellite" made observations of the first target, Cygnus X-1.
The team analyzed the observation data of the "Eye Satellite" on Cygnus X1, and in the longest exposure time (about 150,000 seconds), the low, medium and high energy detectors of the "Eye Satellite" independently and significantly detected a temporary quasi-periodic oscillation signal at a frequency of 88 mHz. By studying the frequency, coherence, amplitude, and changes with energy of this quasi-periodic oscillation signal, the researchers found that X1 Cygnus, which has massive stars, exhibits different characteristics from the X-ray binary stars of the majority of the milky way's small-mass black holes in the Milky Way.
It is worth noting that the Cygnus X1 quasi-periodic oscillation signal detected in the study through the "Eye Satellite" data occurred in the soft state, while the quasi-periodic oscillation signals found in the past in black hole binary stars were mostly detected when the black hole binary was in a hard spectral state. Although similar quasi-periodic oscillation signals may have been detected in Cygnus X1 in the RXTE satellite era, they have never been detected in the hard X-ray energy range above 50keV. Therefore, the detection results show the observation advantages of China's Eye X-ray Astronomical Satellite in high-energy hard X-rays.
At the same time, the findings provide important clues to understanding the phenomenon of millihertz quasi-periodic oscillation (frequency < 100mHz) in massive X-ray binary stars, which may open up new research directions for revealing accretion patterns including X-ray pulsars and ultra-bright X-ray sources from nearby galaxies. Similar to X1 Cygnus is the massive black hole X-ray binary LMC X-1 in the Magellanic Cloud. It has been in a soft-spectrum state for a long time, and scientists can occasionally detect quasi-periodic oscillations of about tens of millihertz. Researchers at the Shanghai Astronomical Observatory believe that the quasi-periodic oscillations detected at LMC X-1 in the Greater Magellanic Cloud are likely to be produced by the same mechanism as the millihertz quasi-periodic oscillations detected in Cygnus X1, and similar millihertz quasi-periodic oscillations have been found in other types of massive X-ray binary stars, such as accretion pulsars in massive X-ray binary stars and super-bright X-ray sources in nearby galaxies. Therefore, this finding may imply that this millihertz quasi-periodic oscillation is related to the accretion pattern of the stellar wind.
Artistic imagination of Cygnus X1 (from NASA/CXC/M. Weiss)
Three instruments of the Vision Satellite independently detect millihertz quasi-periodic oscillation signals from low-energy, medium-energy and high-energy detectors
Source: Shanghai Astronomical Observatory, Chinese Academy of Sciences