From: Kevin Balentine <kevinbalentine@m...>
Date: Mon, 15 Sep 2003 10:33:50 -0500
Subject: A black hole life preserver
The link for this story is: http://www.dallasnews.com/health/columnists/tsiegfried/stories/091503dnl ivtomco l.33516.html I think you have to register to view these stories so I thought I would just post it for everyone to read (I work at The Dallas Morning News so I'm not going to feel guilty for posting the whole thing :-) I have to give Tom kudos for the Highlander reference. Doughnut can delay death for black hole tourist By TOM SIEGFRIED / The Dallas Morning News When you toss an endangered swimmer a life preserver, you should really call it a death delayer. After all, nobody lives forever, except the Highlander, and even he'd be in trouble if he fell into a black hole. Today's question is, when the Highlander dives into a black hole, is there any point in providing him with a death-delaying life preserver? And the answer, actually, is yes, say J. Richard Gott III and Deborah Freedman. Dr.Gott, of Princeton University, and Ms.Freedman, of Harvard, have calculated a way to prolong your life, or at least reduce your agony, as a black hole's gravity sucks you in and rips you to shreds. You just need to surround yourself with a gigantic electrically charged doughnut. If you fall into a black hole unprotected, gravity draws all parts of your body toward the center of the black hole. So your left side will be pulled to the right and your right side to the left. If you go in feet first, the gravitational pull will be much stronger on your shoes than your head, tending to make you instantly thinner and taller. "It is like being stretched on a rack and simultaneously crushed in an iron maiden," the two researchers write in a new paper submitted to the journal Physical Review D. Such gravitational (or "tidal acceleration") forces don't hurt, up to a point. Fighter pilots can withstand forces up to 9 G's or so  nine times the normal pull of gravity. "But beyond 10 G's, the tidal acceleration will cause pain and dismemberment," the scientists write in their paper, available on the World Wide Web at xxx.lanl.gov/abs/astro-ph/0308325. So at some point, your journey to the black hole's center will turn into painful torture. (Actually, the torture can begin even before you reach the black hole's outer boundary, the event horizon. For large black holes  greater than 13,800 times the mass of the sun  crossing the event horizon remains within the acceptable range of G-forces. But small black holes have masses of only a few suns. For those, you'll start stretching before you cross the border.) Anyway, the good news is that the time of torture passes pretty quickly. In fact, from the start of the pain to getting crunched out of existence altogether comes to less than a 10th of a second, the scientists calculate. But a life preserver  er, death delayer  can prolong your pain-free travel time and make the torture time even shorter. It has to be big  about the size of one of Saturn's rings and the mass of a large asteroid. But when diving into a black hole with this huge ring surrounding you, the pull of the ring on you will cancel the pull of the black hole. As you fall closer to the black hole's center, its pull on you increases. But the black hole tugs on the ring, too, compressing it so that more of its mass is closer to you. So the ring's pull on you increases, counteracting the black hole's efforts to crush you. "Your head is being pulled downward by that ring, and your feet are being pulled upward, so it just counters the tidal force that the black hole is giving," Dr.Gott said in a telephone interview. To keep the ring from collapsing under its own weight, it must be electrically charged (electrical repulsion counters the ring's self-gravity). Unfortunately, the electrical fields would fry you, so you need to encase yourself in a protective container known as a Faraday cage. But that's pretty simple compared to making the giant doughnut to begin with. If all works well till then, the ring can keep you comfortable up to 6,760 G's. After that you'd be tortured for a mere three one-thousandths of a second. "You really wouldn't know what hit you," Dr.Gott and Ms.Freedman write. If that still bothers you, you can reduce the torture time even more. Instead of falling in feet first, assume the fetal position. Then align the line connecting your shoulders so it points toward the black hole's center. With a ring suitably adjusted for your new size, you can reduce the torture time to less than two one-thousandths of a second. Of course, another approach to avoiding such torture is simply staying away from black holes. But that's not very much fun. And having fun with black holes is what such exercises are all about. "This business that you're ripped apart when going into a black hole is something that's said in every astronomy book," Dr.Gott said. "We just wondered if there was something you could actually do about it." The calculations in the Gott-Freedman paper can be grasped by a bright high school student; these death-delaying scenarios offer insights into the basics of Einstein's general relativity and fundamental principles of physics. Analyzing such seemingly silly situations can give students  and scientists  a more tangible grasp of what nature is really like in realms outside earthbound experience. Besides, there really could be practical applications someday, when interstellar travelers want to explore black holes or perhaps neutron stars. Maybe some sort of doughnutlike death delayer would help keep you alive when encountering such objects. "An adjustable-radius, actively oriented life preserver might enable you to venture closer than would otherwise have been the case," the scientists write, "and still return safely home from the adventure."