Summary of “How Supermassive Black Holes Were Discovered”

While the concept of a star collapsing to a black hole is astounding, the possibility that material from millions and even billions of stars can condense into a single supermassive black hole is even more fantastic.
Very strong sources of radio waves were discovered and, when accurate positions were determined, many were found to be centered on distant galaxies.
How are immense radio lobes energized? Their symmetrical placement about a galaxy clearly suggested a close relationship.
The minimum energy needed to power some radio lobes can be equivalent to the total conversion of 10 million stars to energy! Note the thin trails of radio emission that connect the lobes with the bright spot at the center, where all of the energy originates.
In 1974, a very compact radio source, smaller than 1 second of arc was discovered there.
How much of the dark mass within the stellar orbits can be directly associated with the radio source Sgr A*? Were Sgr A* a star, it would be moving at over 10,000 kilometers per second in the strong gravitational field as other stars are observed to do.
Finding that the compact radio source Sgr A* is at the precise location of the unseen mass and is motionless provides even more compelling evidence for a supermassive black hole.
He uses radio telescopes across the globe simultaneously to obtain the highest resolution images of newborn and dying stars, as well as black holes.

The orginal article.