Have black holes always fascinated you? Well, all you need is a 20 cm telescope to observe a nearby active black hole.
Researchers from Kyoto University have reported that the activity of such phenomena can be observed by visible light during outbursts and that flickering light emerging from gases surrounding black holes is a direct indicator of this.
The team's results indicated that optical rays and not just X-rays provided reliable observational data for black hole activity.
Author Mariko Kimura said that they now know that they can make observations based on optical rays and that black holes can be observed without high-spec X-ray or gamma-ray telescopes.
Once in several decades, some black hole binaries undergo outbursts, in which enormous amounts of energy including X-rays are emitted from substances that fall into the black hole.
Black holes are commonly surrounded by an accretion disk, in which gas from a companion star is slowly drawn to the hole in a spiral pattern. Activities of black holes are typically observed through X-rays, generated in the inner portions of accretion disks where temperatures reach 10 million degrees Kelvin or more.
V404 Cygni, one of the black hole binaries thought to be nearest to Earth woke up after 26 years of dormancy on 15 June 2015 as it underwent such an outburst.
During the research, the team succeeded in obtaining unprecedented amounts of data from V404 Cygni, detecting repetitive patterns having timescales of several minutes to a few hours. The optical fluctuation patterns, the team found, were correlated with those of X-rays.
The study also revealed that these repetitive variations occur at mass accretion rates lower than one tenth of that previously thought. This indicates that the quantity of mass accretion rate isn't the main factor triggering repetitive activity around black holes, but rather the length of orbital periods.
The research is published in the journal Nature.
