Such an event will cause a flash in the sky, as well as the arrival of a powerful gravitational wave. A gravitational wave is a distortion of space-time. That is, time begins to slow down or go backwards, space “pulsates”. How it looks in reality, no one knows, because this has never happened before.
Gravitational waves come to Earth from time to time, but they are very weak.
The galaxy in question is 1 billion light-years away. Very far away, and this is good: the phenomena will not be catastrophic.
At the center of this distant galaxy are two black holes, one revolving around the other. Their total mass is about 800 million times greater than the Sun, while by cosmic standards they are tiny, smaller than the size of the Earth’s orbit. Black holes are approaching, then receding. As they approach, there is a small flash.
Astronomers have been watching these flashes for a long time, and they have noticed that flashes are becoming more frequent.
A few years ago, such an outbreak happened once a year. Now it’s once a month. This means that the smaller black hole is rapidly approaching the larger one.
When will it happen? It is hard to say. According to some astronomers, until the full merger – a maximum of a thousand days. That is, it will happen either this year or next year.
According to NASA’s Jet Propulsion Laboratory in California estimates that if one were to take into account the many millions of years these black holes have likely been orbiting each other, they are now more than 99 percent of the way to a collision. In real terms, that means a collision around 10,000 years from now.
Earthlings will see a flash in the sky, hardly very bright (normally this galaxy is not visible to the naked eye). One can only speculate about the further consequences. The merger of black holes is the most powerful catastrophe that can only be expected in our universe.