Black holes seem to appear frequently in the news, recently. I was especially impressed by the details about the black hole in the center of our galaxy. Its mass is estimated at 3 million times the mass of the sun. This could be estimated by a star that goes around the black hole once in 15 years. At its "periholion" (1) it approaches the black hole to 17 light-hours, and moves at the incredible speed of 5000 km/s (almost 200 times the speed of the earth around the sun).
Hilmar.
(1) Perihelion = closest approach to the sun (in an orbit), Periastron = closest approach to a star, etc.
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)
