I am a student in physics at Bishop Luers High School, Fort Wayne, Indiana. We have been studying physics and this is part of an assignment from my teacher. Here is my question: How far away is the closest black hole?
The closest known black holes are stellar mass black holes in our galaxy. These black holes have so far only been seen when they are in close contact with another star which is orbiting around them (well really they orbit each other). The black hole accretes material from the star and this produces a lot of energy. When jets are produced the systems are known as microquasars (by analogy with extragalactic quasars) and can be observed at many wavelengths, but usually are most distinctive in X-rays.
Here is a page with a summary of known microquasars. Note: not all black hole systems that are known are microquasars.
All of these microquasars are within about 24 thousand light years of Earth. As of now the closest known one is thought to lie at about 1,600 light years from Earth. You can read about it in this space.com article.
Update by Michael Lam, July 17, 2015: This question was answered in February, 2002. However, observations published in July, 2001 showed that V4641 Sgr, mentioned in the space.com article, had to be at least 15 times farther away than previously thought. The current nearest, published in 2007, is V616 Mon, also known as A0620-00. Additional information can be found via the University of Texas McDonald Observatory StarDate page (last modified 2/12/2012).
This page was last updated July 17, 2015.