Saturday science subject: Flying into a black hole
Nature has published an interesting feature about black holes and what might ensue if an astronaut in a hypothetical space ship were sucked into one of them.
Falling into a black hole is a strange affair. Because the hole's gravity distorts space-time, a far-off observer watching an object crossing the event horizon sees time for that object appear to slow down — a clock falling into a black hole would appear, from the outside, to tick ever slower. At the horizon itself, time stops, and the object stays frozen there for the remaining lifetime of the Universe.
But this isn't how things seem to the in-falling object itself. Indeed, if the black hole is big enough, nothing noticeable happens when a spaceship crosses its event horizon — you could stray inside without realizing. Yet once inside, nothing can save you from being crushed by the hole's gravity sooner or later.
The article gives a few pointers for delaying the inevitable (being crushed into a singularity). According to Geraint Lewis from the University of Sydney in Australia, the "longest road" once a space ship is past the black hole's event horizon is free fall starting from rest. "If you cross the event horizon on one of the shorter roads, you can fire your rocket to move you on to the longest road," he says. Assuming a super-massive black hole, such as the one that's believed to reside at the center of the Milky Way, the longest survival time "might be hours"—perhaps enough to learn to play a new tune on the flute.