Don't get sucked in without one.

As anyone falling into a black hole would tell you--if only they could--the trip ends badly.

Actually, for all but the last moment, things would be fine. As you began approaching the great abyss, you'd be in free fall, experiencing weightlessness. But as you got very close or ventured inside the hole, watch out.

If you fell in feet first, the hole would pull harder on your toes than your head, because the top of your body would lie farther from the hole's center. Similarly, the uneven tug exerted by the hole would compress your shoulders as though they were in a vise. Because of these differences in gravity, you'd be simultaneously ripped apart vertically and squeezed horizontally. From the instant these tidal forces became too much to bear, death would occur in just under a tenth of a second.

Although death is unavoidable, is there any way to delay it and shorten the agony?

According to two researchers who actually took the time to contemplate the problem, the answer is yes. But you have to take along the right equipment, assert Princeton University cosmologist J. Richard Gott and Deborah L. Freedman of Harvard University. The essential item resembles a life preserver--a thin ring massive enough to counteract the black hole's tidal forces. The ring would have to be as heavy as a large asteroid and could be as large as one of the rings of Saturn, says Gott. The researchers have posted their whimsical analysis online (http://xxx.lanl.gov/abs/astro-ph/0308325).

Kept at waist level, the ring would exert an upward tug on your feet and a downward pull on your head, counterbalancing the black hole's uneven tug on different parts of your body. As the traveler approached the black hole and the tidal forces from it increased, the ring would shrink and exert correspondingly larger countertidal forces. The massive ring would have to be electrically charged to keep it from collapsing.

The ring counters the black hole's tidal forces up to a whopping 6,760 g's--676 times the gravity a human body can withstand. That would give a black hole diver an extra 0.09 second to remain in one piece. It also means that tidal forces would begin to overwhelm the explorer only during the last 0.00346 second of the journey, a time so short "you'd never know what hit you," says Gott.

The notion that it's possible to even temporarily prevent tidal dismemberment of any object that gets too close to a black hole is "something no one had shown before," says Freedman.

This intellectual exercise could have a practical application. In venturing near a dense star called a neutron star, or touring the outskirts of a small black hole, such a life preserver would enable a space traveler to "venture closer than would otherwise have been the case and still return safely home from the adventure," the researchers note.

"This idea could make a nice problem in a textbook ... but will not have much wider implications," says Avi Loeb of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.