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Our long years of research have shown that black holes can exist with various masses and in various locations in the universe, as illustrated in this chart. The horizontal axis indicates the distance from our solar system, and it is divided into four areas for the sake of convenience: our Galaxy, nearby galaxies, the distant universe, and the early universe. The vertical axis indicates the mass of the black holes, with the sun used as the unit of comparison.
Before the mid-1990s, we knew of only two kinds of black holes: one was similar to Cygnus X-1, whose mass is around 10 times larger than the sun, and the other is the kind found at the center of a galaxy. The raising of Japan's national flag in the chart is meant to commemorate Professor Oda's achievements.
Around 1995, we came to understand that ordinary-looking galaxies near ours actually have gigantic black holes located at their center. (It is important to mention the achievements of Dr. Makoto Miyoshi, Dr. Naomasa Nakai, and Dr. Makoto Inoue.) As I mentioned earlier, we have also discovered some small black holes in nearby galaxies that are similar to Cygnus X-1, and also intermediate-mass black holes, which we had not known about earlier. We can also now say for certain that when collapsed stars change into black holes, they send gamma-ray bursts far throughout the universe.
There are different kinds of black holes in terms of mass, and they seem to play an important role in the evolution of the universe. This is the latest information on the research of black holes.
[Lecture venue (Tokyo International Exchange Hall): February 27, 2004]
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