Black Holes and Neutron Stars
X-ray Bears during a press conference on 25 October at the first gathering of Chinese space explorers in Xiamen.
X-ray binaries are binary stars that emit X-rays and consist of a normal star and either a neutron star or a black hole. The gravity of the very dense neutron star or black hole drops material from the normal star on it, creating a rapidly rotating accretion disk that emits intense X-rays. X-ray binaries are an important research goal for those who seek to understand strong gravitational and magnetic fields and the matter that affects them.
The Insight XHMT scientists were able to investigate quasi-periodic oscillations (QPOs) in X-rays from black holes binary files up to 100 keV, an increase from the previous upper limit of 30 keV. They showed the energy dependence of the QPO amplitude and the centroid frequency in the range of 1 to 100 keV. These achievements surpass previous satellites and open a new window for the investigation of black holes.
A detailed timing study of the brightest persistent X-ray source Sco X-1 was also performed with Insight HXMT data. The findings revealed three key findings: 1) All types of QPOs are derived from non-thermal emissions; 2) The innermost part of the accretion disk is not thermal; and 3) The corona is geometrically inhomogeneous.
For the first time, scientists observed the sudden change in the accretion disk state when the X-ray intensity of a neutron-star X-ray binary reached a certain value. This confirmed the theory put forward almost 50 years ago that the radiation pressure of light causes a structural mutation of the accretion disk.
In the past, corona cooling was detected by stacking a series of short type I bursts that occurred during the low / hard state event of a neutron star x-ray binary. The current study is the first time that a very hot corona – usually at a high temperature of several hundred million degrees – is rapidly cooled by a "shower" of low-energy X-ray photons from a single thermonuclear eruption on the surface of a neutron star. This method provides an almost unique means of investigating the physical properties and heating mechanism of high temperature corona. Also, the interaction between a thermonuclear burst and an accretion disk detected in a single burst is likely to be a new method of constraining the innermost radius of the accretion disk.
In addition, scientists confirmed that the energy of the X-ray cyclotron absorption line increases famous neutron star X-Binary Her X-1 does not take off anymore. The data demonstrate that the magnetic field strength near the X-ray range has become stable after almost 20 years of slow decline.
Insight-HXMT has witnessed many black holes, neutron stars, as China's first X-ray astronomy satellite, and high-precision cadence bursts since launch on June 15, 2017. The satellite consists of three lamellar collimated X-ray telescopes – the High Energy X-ray Telescope, the Medium Energy X-ray Telescope, and the low-energy X-ray telescope – as well as a space monitor.
So far, the satellite has performed more than a thousand observations and generated 29 TB of scientific data. In total, more than 10 scientific papers have been accepted or published in the most important international journals for astrophysics. Further important research results are still in the publication pipeline.