X Marks the Spot

ASTRONOMERS HAVE LONG SUSPECTED THAT THE Whirlpool galaxy, 20 million light- years away, harbors in its core a black hole, a superdense knot of matter whose gravity is so powerful that even light can't escape. Now a photograph taken by the Hubble Space Telescope has convinced them. The picture, released last week, reveals a giant X at the galaxy's center. The scientists think one arm of the X is a massive, doughnut-shaped cloud of dust swirling around the hole. The doughnut is seen edge on, hiding the black hole from view, but two cone-shaped beams of light emitted by hot gas closer in can be seen escaping out the sides. As for the second arm, no one knows what it is.