For Further Exploration: Black Holes and Curved Spacetime
Charles, P. & Wagner, R. "Black Holes in Binary Stars: Weighing the Evidence." Sky & Telescope (May 1996): 38. Excellent review of how we find stellar-mass black holes.
Gezari, S. "Star-Shredding Black Holes." Sky & Telescope (June 2013): 16. When black holes and stars collide.
Jayawardhana, R. "Beyond Black." Astronomy (June 2002): 28. On finding evidence of the existence of event horizons and thus black holes.
Nadis, S. "Black Holes: Seeing the Unseeable." Astronomy (April 2007): 26. A brief history of the black hole idea and an introduction to potential new ways to observe them.
Psallis, D. & Sheperd, D. "The Black Hole Test." Scientific American (September 2015): 74–79. The Event Horizon Telescope (a network of radio telescopes) will test some of the stranger predictions of general relativity for the regions near black holes. The September 2015 issue of Scientific American was devoted to a celebration of the 100th anniversary of the general theory of relativity.
Rees, M. "To the Edge of Space and Time." Astronomy (July 1998): 48. Good, quick overview.
Talcott, R. "Black Holes in our Backyard." Astronomy (September 2012): 44. Discussion of different kinds of black holes in the Milky Way and the 19 objects known to be black holes.
Bartusiak, M. "Catch a Gravity Wave." Astronomy (October 2000): 54.
Gibbs, W. "Ripples in Spacetime." Scientific American (April 2002): 62.
Haynes, K., & Betz, E. "A Wrinkle in Spacetime Confirms Einstein’s Gravitation." Astronomy (May 2016): 22. On the direct detection of gravity waves.
Sanders, G., and Beckett, D. "LIGO: An Antenna Tuned to the Songs of Gravity." Sky & Telescope (October 2000): 41.