Observations

Black Holes
Black hole page from NASA's "Imagine the universe!" site; includes a section on observational aspects - "If We Can't See Them, How Do We Know They're There?"
http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html

Do Black Holes Exist?
Brief text by Pablo G. Ostrov about the evidence for the existence of black holes, aimed at a general audience.
http://pgostrov.googlepages.com/e3.html

Field Guide to X-ray Sources
Pages on the website of the Chandra X-Ray Observatory; includes information about stellar, mid-mass and supermassive black holes, Chandra images, and a podcast.
http://chandra.harvard.edu/xray_sources/blackholes.html

XMM: Black Holes and Quasars
Educational pages on the website of the space-borne X-ray telescope XMM, hosted by the University of Birmingham. Information about black holes and other astronomical sources of X-rays.
http://www.sr.bham.ac.uk/xmm/blackholes.html

Black Holes in Astrophysics
Review article by Ramesh Narayan (Harvard-Smithsonian Center for Astrophysics) about the astrophysical evidence for black holes. <small>(June 14, 2005)</small>
http://arxiv.org/abs/gr-qc/0506078

The Afterglow of Massive Black Hole Coalescence
Article by Milos Milosavljevic and Stearl Phinney; describes the kind of afterglow that should be visible for X-ray telescopes when two massive black holes merge. <small>(March 14, 2005)</small>
http://arxiv.org/abs/astro-ph/0410343

Radio Astronomers Lift 'Fog' on Milky Way's Dark Heart
Press release by the National Radio Astronomy Observatory about observations of the immediate neighborhood of our galaxy's central supermassive black hole. <small>(April 1, 2004)</small>
http://www.nrao.edu/pr/2004/sagastar/

Study of Accretion Processes on Black Holes: Fifty Years of Developments
Review article by Sandip K. Chakrabarti of the research done on one of the main mechanisms by which black holes cause highly luminous phenomena in their immediate neighborhood. <small>(February 24, 2004)</small>
http://arxiv.org/abs/astro-ph/0402562

Detection of Hard X-ray Emission from the Galactic Nuclear Region with INTEGRAL
Article by Guillaume Belanger and colleagues; recounts X-ray observations of the neighborhood of our galaxy's central black hole. <small>(November 7, 2003)</small>
http://arxiv.org/abs/astro-ph/0311147

Evidence for the Black Hole Event Horizon
Review article by Ramesh Narayan about possible observational evidence for the defining feature of black holes. <small>(October 23, 2003)</small>
http://arxiv.org/abs/astro-ph/0310692

Closest Star Seen Orbiting the Supermassive Black Hole at the Centre of the Milky Way
Article by R. Schodel and colleagues (Max Planck Institute for Extraterrestrial Physics) about the best evidence to date for the existence of a supermassive black hole in the center of our own galaxy - the way it influences the orbits of nearby stars. <small>(October 18, 2002)</small>
http://arxiv.org/abs/astro-ph/0210426

Astrophysical Evidence for the Existence of Black Holes
Review article by Annalisa Celotti, John C. Miller, and Dennis W. Sciama (SISSA, Trieste) about the current state of the search for observational evidence for the existence of both stellar-mass and supermassive black holes. <small>(December 9, 1999)</small>
http://arxiv.org/abs/astro-ph/9912186

Hubble Space Telescope Discovers Disk Fueling Possible Black Hole
News item published on the website of the Space Telescope Science Institute. <small>(November 19, 1992)</small>
http://hubblesite.org/newscenter/archive/releases/1992/27/text/