Binary Black Hole Revealed
Experts managing the Monitor of All-sky X-ray Image (MAXI) instrument, an exposed facility (EF) experiment aboard the International Space Station (ISS), have just released a detailed view of the Universe showing the location of bright X-ray sources and binary black hole systems.
From its orbital perch, attached to the outer hull of the station, the device is capable of conducting a full sky survey every 92 minutes. Its main mission is to look for and monitor bright sources of X-ray radiation throughout the entire sky.
One of the reasons for which this mission was sanctioned is because astrophysicists still don’t understand some of the unusual behaviors and distributions that X-ray sources have in the Universe.
The most difficult aspect of MAXI’s mission is to keep track of both known and unknown X-ray sources. Considering that flashes of radiation may be generated by supernova explosions, and that the precursor stars for these explosions are located all over the place, the mission becomes very complex.
“Most visible stars shine with energies generated by nuclear fusion in their cores. In these stars, if the energy generated in their core increases more than usual, the whole object expands and eventually lowers the core temperature,” explaions Nobuyuki Kawai.
“In this way, negative feedback is activated to stabilize the nuclear reaction. For this reason, these stars shine very stably for most of their lifetime,” adds the expert, who holds an appointment as a researcher at the Tokyo Institute of Technology.
However, MAXI was not directed towards observing these objects. For the past 18 months or so, the instrument’s time has been dedicated to searching for black hole binary systems such as Cygnus X-1.
These systems are made up of two objects, of which one or both is a black holes. There are binary systems which are made up of a black hole and a neutron stars, or various other combinations.
All these systems have either a soft or hard state of energy, which is dependent on the density of the gas that surrounds the two objects. “We can get a clue to estimate the mass of a black hole by examining the X-ray intensity and radiation spectrum in the soft state,” Kawai explains.
“As a result of analysis of the motion of the companion star rotating the center of gravity of the binary system, we found that Cygnus X-1 is a remarkably smaller object than normal stars, with an X-ray source mass about 10 times the solar mass but which emits hardly any visible light,” he adds.