Text Box: Chandra x-ray images of the nebulae surrounding the Crab and Vela pulsars (Fig. 5 [not reproduced here]) show toroidal and jet structures, demonstrating that pulsar winds are far from isotropic [M. C. Weisskopf et al., Astrophys. J. 536, L81 (2000); D. J. Helfand et al., Astrophys. J. 556, 380 (2001)]. The symmetry of these systems indicates that both structures are related to the rotation axis of the underlying pulsar: the jets along the polar axis, and the toroidal structures in or near the equatorial plane. Images of the Crab Nebula taken at intervals of weeks and months by the Hubble Space Telescope and Chandra [J. J. Hestor et al., Astrophys. J. 577, L49 (2002)] show that the wind structures are dynamic, with moving features implying outflow velocities on the order of half the velocity of light in the equatorial disk and the polar jets. It remains a challenge for pulsar theorists to account for even the broad characteristics of these outflows. For the Crab and Vela pulsars, the projected direction of the pulsar rotation axis implied by the x-ray data is very close to the projected direction of the pulsar's space velocity [P. A. Caraveo, R. P. Mignami, Astron. Astrophys. 344, 367 (1999); R. Dodson et al., Astrophys. J. 596, 1137 (2003)]... A recent analysis [C. Y. Ng, R. Romani, Astrophys. J. 601, 479 (2004)] suggests that this correlation holds for several other pulsars with associated PWNs [pulsar wind nebulae]. ... Observational Properties of Pulsars, R. N. Manchester (Australia Telescope National Facility, CSIRO, New South Wales), Science 304, 542-546 (23 April 2004)
Text Box: Ancient thinkers were much troubled in trying to discover what forces actually maintain the motion of the thrown stone. Max Born, Einstein’s Theory of Relativity, Dover Publications, NY, 1965; p 29
Text Box: What causes the pulsar, or pulsating radio star, to emit those extremely regular pulses of radio waves? What keeps the thrown stone in motion? What is magnetism? Unconnected though such phenomena may seem to us now, they all find related answers in the final insight here into the fundamental nature of things... with two and only two laws assumed a priori: the conservations of mass-energy and the asymmetry of its motion (a nonvanishing seminal linear momentum coupled with a spin).
Text Box: As a child, the Nobel Prize-winning physicist Richard Feynman asked his father why a ball in his toy wagon moved backward whenever he pulled the wagon forward. His father said that the answer lay in the tendency of moving things to keep moving, and of stationary things to stay put. "This tendency is called inertia," said Feynman senior. Then, with uncommon wisdom, he added: "But nobody knows why it is true." That’s more than even most physicists would say. To them, inertia does not need explaining, it simply "is." But since the concept was first coined by Galileo in the 17th century, some scientists have wondered if, perhaps, inertia is not intrinsic to matter at all, but is somehow acquired. Those who have tried to come to grips with inertia include Feynman junior, once he had grown up, and Albert Einstein, who tried – and failed – to show that inertia was related to the arrangement of matter in the universe. In 1872, [the German philosopher-physicist Ernst] Mach argued that acceleration – and hence inertia – is not absolute, but only has meaning within a frame of reference. For Mach, that frame of reference consisted of the other matter in the universe: After all, in utterly empty space, how do you know you are moving? Einstein later tried and failed to work that notion into general relativity.. Inertia: Does Empty Space Put Up the Resistance? Robert Matthews, RESEARCH NEWS, Science 263, 612 (4 Feb 1994)