The closest black hole whose exact distance to Earth is known is Cygnus V404.This black hole is a normal star and a binary star that orbits each other.In such a celestial body, powerful light is emitted by the gas flowing from a normal star toward a black hole, and this phenomenon is called outburst.There was a growing expectation that the V404 star in Cygnus would cause an outburst about once every ten or so years, and that the last time it happened in 1989, the outburst would be observed again from around 2000. ..And from June to July 2015, it caused an outburst for the first time in 6 years.

　Outbursts have been known from past observations to emit intense X-ray-like light.However, when observing this outburst, we were able to observe not only X-rays but also visible light blinking.It was unthinkable from the conventional wisdom that visible light is emitted from a black hole, which is said to absorb even light.However, this discovery has overturned it.

　This discovery shows the possibility of observing black holes with ordinary telescopes without using special observation equipment.In other words, it is expected that research on black holes will be possible at a lower cost, which will accelerate research.The same thing may have happened to celestial bodies that cause outbursts other than black holes, and we would like to apply the results of this research.