In an international collaboration between Japan and Sweden, scientists explained how gravity affects the shape of matter near the black hole in the binary system Cygnus X-1. Their findings, published this month in Nature Astronomy could help scientists better understand the physics of strong gravitation and the evolution of black holes and galaxies.
Near the constellation of Cygnus, a star is orbiting the first black hole discovered in the universe. Together they form a binary system known as Cygnus X-1. This black hole is also one of the brightest X-ray sources in the sky. The geometry of the matter that generates this light, however, was uncertain. The research team revealed this information from a new technique called X-ray polarimetry.
Taking a black hole is not easy. For one, it is not yet possible to observe a black hole because the light can not escape. Instead of observing the black hole itself, scientists can observe light coming from matter near the black hole. In the case of Cygnus X-1
Most of the light we see, as from the sun, vibrates in many directions. Polarization filters light so that it vibrates in one direction. With polarized glasses, snow goggles make it easier for skiers to see where they are going downhill – they work because the filter reflects the light from the snow.
"It's the same situation with hard X-rays around a black hole," Hiromita Takahashi told Hiroshima University Assistant Professor and fellow students. "But hard X-rays and gamma rays coming from near the black hole penetrate this filter, there are no such" goggles "for these rays, so we need another special kind of treatment to direct and measure this light scattering . " 19659003] The team had to find out where the light came from and where it was scattered. To perform these two measurements, they started an x-ray polarimeter on a balloon called PoGO +. From there, the team was able to put together what proportion of the hard X-ray radiation was reflected off the accretion disk and identify the shape of the matter.
Two competing models describe how matter near a black hole in a binary star system can look like Cygnus X-. 1: the lamppost and the advanced model. In the lamp post model, the corona is compact and tightly tied to the black hole. Photons bend towards the accretion disk, resulting in more reflected light. In the extended model, the corona is larger and distributed near the black hole. In this case, the light reflected from the disk is weaker.
Since the light did not bend so much under the heavy gravity of the black hole, the team concluded that the black hole fit into the extended corona model
information allows researchers to uncover more features about black holes. An example is its rotation. The effects of spin can change the spacetime around the black hole. Spin could also give hints on the development of the black hole. It could be that the speed slowed since the beginning of the universe or that matter is accumulated and turns faster.
"The black hole in Cygnus is one of many," said Takahashi. "We would like to study more black holes with X-ray polarimetry, such as those closer to the center of galaxies, and we may understand the development of black holes as well as the evolution of galaxies."
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