Twisting space-time and devouring anything—even light—that gets too close, black holes rank among the most bizarre objects in the cosmos. Theory predicts that these gravitational beasts are surrounded by a so-called event horizon, a one-way threshold through which things can fall in but nothing can get out.
Two studies reported at last week's meeting of the American Astronomical Society (AAS) in San Diego provide new evidence for event horizons.
Analyzing a trove of data collected nearly a decade ago by the Hubble Space Telescope, astronomers observed what seems to be the last gasp emitted by gaseous material spiraling into Cygnus X-1, a suspected black hole 6,000 light-years from Earth.
Joseph F. Dolan of NASA's Goddard Space Flight Center in Greenbelt, Md., and his team found that blobs of hot gas orbiting Cygnus X-1 radiated pulses of ultraviolet light that grew fainter and more rapid and then disappeared.