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OJ 287 is recognized as a binary black hole system with a slowly spiral orbit caused by energy loss by gravitational radiation. This energy loss was already confirmed in 2008. Subsequent measurements have confirmed this orbit solution, most recently in 2023.
Until now, the signals coming from the binary system have been associated with the ultramassive primary black hole or with the gas accretion disk surrounding it.
However, an international research group recently acquired new evidence regarding this system by observing signals coming directly from the smaller (secondary) black hole. Using this evidence, the researchers claim they can ‘see’ the secondary black hole for the first time by using measurements of polarized light coming from OJ 287.
The study was published October 30 in The Astrophysical Journal Letters.
Scientists have known for more than 50 years that the light from OJ 287 is polarized. However, to make full use of this polarized signal it is necessary to monitor its variation over time.
For the current study, the researchers completed the most extensive polarization monitoring to date using seven telescopes in the US, Japan, etc. with special equipment for measuring polarization.
“We found a general rule that OJ 287 follows: the increase in total optical emission leads to increase in polarization, and vice versa,” says Prof. Alok C. Gupta, the recent PIFI visiting scientist at the Shanghai Astronomical Observatory from the Chinese Academy. of Sciences, the study’s first author, and professor at India’s Aryabhatta Research Institute of Observational Sciences.
Interestingly enough, however, there are times when this rule fails. Models show that the disruptions are likely related to two overlapping signals, one coming from the primary black hole and the other coming from the secondary black hole. This evidence for two separate signals is most evident in the polarization of light, which is expected to be very different when two sources contribute, rather than just a single source. The general rule of polarization variation is violated in the case of two signals.
Because the two black holes are so close together in the sky, only about 10 microarcseconds apart, they necessarily appear as a single point of light. “Only by using the polarization of light can we be reasonably confident that there are actually two sources, two black holes, contributing to the total light signal,” said Prof. Gupta. ‘The violations of the general rule occur at times when we expect the secondary black hole to be active in the binary model: generally the signal from the smaller secondary black hole is not observable. The activity of the secondary black hole is related to its approach to the binary model. primary gas disk, which provides matter for the secondary to feed on.”
The power supply produces clear signals, from radio to gamma radiation. These latter signals have recently been used to verify the orbit model. “Now the polarization data confirm this interpretation. As a result, we are convinced that OJ 287 is truly an ultramassive binary black hole system, and signals from both components can be separated despite their proximity to each other in the sky,” said Prof. GU Minfeng of the Shanghai Astronomical Observatory of the Chinese Academy of Sciences, co-author of the study.
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