The search for gravity’s kiss
This book is for readers interested in learning the scientific, historical, and personal stories behind the detection of gravitational waves. This story is an incredible scientific odyssey. It conveys a sense of awe and excitement about a century of scientific investment of time, labor and technology. The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory to detect cosmic gravitational waves. This instrument can detect a change in the distance from Earth to Proxima Centauri (distance of 4.24 light years) with an accuracy smaller than the width of a human hair. As of March 2018, LIGO made six detections of gravitational waves from six different sources; the first five were colliding black-hole pairs, and the sixth was due collision of two neutron stars Neutron stars simultaneously produces optical signals detected by gamma ray satellites and optical telescopes. The orbiting planets, orbiting stars, binary stars do not emit detectable level of gravitational waves. But neutron star mergers and black hole collisions produce enough unwarping of spacetime and energy to carry through the universe.
The highlight of this book is about the first detection gravitational wave referred to as GW 150914. The characteristic chirp of GW150914 most closely matched the theoretical prediction of waveform for two black holes with 36 and 29 times the mass of Sun. This originated in a remote galaxy. Two black holes (with a diameter of few hundred miles) were orbiting each other. They were swirling each other for millions of years, and as they approached each other at half the speed of light and they merged within a fraction of seconds resulting in a black hole of 62 solar mass. The equivalent three solar mass was converted into energy released in the form intense electromagnetic radiation, and the intensely warped spacetime under the gravity of black holes were released as gravitational (spacetime) waves. Immediately after the event horizon, spacetime stretched and elongated in its path like waves. Thus partially separating the components of matter in its path; the atomic nuclei, electronic structure of atoms and molecules were instantly destabilized from their configurations. In much of physics, spacetime is treated as static fabric upon which matter and energy behave according to laws of physics. But here the spacetime itself becomes active participants in the operation of physics. Heavier elements (beyond iron of the periodic chart) originates during the black hole/neutron star mergers and part of it could be due to disruption of space and reassembly of nucleus. Fortunately for life, these cataclysms occur less than once in a million years in Milky Way Galaxy, according to physicist Martin Rees.
General Relativity predicted that spacetime produces gravitational waves; gravity is essentially bending of spacetime in presence of matter. Large cosmic bodies like neutron stars and black holes produce very large curvature in spacetime. Two effects operates according to relativity: Taking earth as an example, the geodetic effect (spacetime as curvature (“the missing inch”). This is the amount by which the earth wraps the local spacetime in which it resides. Number two, the frame-dragging effect (the rotating matter drags spacetime (spacetime as viscous fluid): The amount by which the rotating earth drags local spacetime around with it.
Generally the analogy of a bowling ball on trampoline is visualized for spacetime bending in presence of large cosmic bodies. Spacetime is highly elastic like trampoline, and earth produces a symmetrical curvature around it like a bowling ball on trampoline (geodetic effect). When we spin the bowling ball on its own axis, this trampoline curvature around the spinning bowling ball will not be symmetric anymore, but this spinning motion will drag along the fabric of the trampoline to a small but noticeable effect. This produces an additional effect, relatively smaller (than geodetic effect) in the precession of the rotational axis of bowling ball. This is called rotational frame-dragging. A combination of these two effects produce a gravitational (spacetime curvature) wave. To help this visualization even better, one must remember that spacetime does not have matter or energy like trampoline, and space does not need matter or energy to exist. The orbiting planets, and stars do not emit detectable level of gravitational waves although they exist. Hence colliding neutron stars and black holes emit detectable waves because of their intense gravity that warps enormous amount of spacetime. A category 5 hurricane produces up to 180 mph of wind, and the eye of the hurricane could be longer than one mile deep in the ocean. This wind power help the hurricane to pack up enormous amount of water and unleash it upon hitting the land. Black holes also warp spacetime and unleash it upon collision with another black hole.
This is an interesting book for anyone interested in the experiences of detecting gravitational waves. This is a highly readable book; recommended.
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