What KDE4 proofed is that you can also sit down and have really interesting conceptual changes that get introduced as big shifts.
What KDE4 proofed is that if you make really awful software that is full of bugs even long term fans will switch to using an alternative.
Sagittarius A* object at the center of our galaxy has a mass of at least 3.7 million solar masses
What the author is refering to is stellar mass black holes, ie. black holes that form from core collapse in star. The Supermassive black holes such as the one in our galaxy are a different beast entirely.
Today is a good day for information-gathering. Read someone else's mail file.