Telescopes will never peer inside a light-swallowing black hole, but they could soon reveal the event horizon, the surface beyond which a black hole traps light permanently. The horizon would absorb light originating from behind a black hole, creating a shadow visible at high enough resolution. Around the shadow would be a bright ring of focused light, like the corona in an eclipse. Astronomers recently acquired the sharpest image yet of the object presumed to be our galaxy's central black hole, thanks to the Very Long Base line Array, an 8,000- kilometer-wide system of 10 radio telescopes. Boosting such telescopes' resolution just four times should clarify the event horizon within the decade, according to a commentary published with the November 3, 2005, Nature.
This article was originally published with the title "On the Horizon" in Scientific American 294, 1, 32 (January 2006)