In his 1994 book Black Holes and Time Warps, physicist Kip Thorne wrote of the tantalizing discoveries to come in the 21st century. In particular, the existence of gravitational waves—ripples in the fabric of space and time—might soon graduate from theoretical prediction to known fact. And those waves could carry all-important hints about their origins in the motion or collision of extremely massive objects.

“Gravitational-wave detectors will soon bring us observational maps of black holes, and the symphonic sounds of black holes colliding—symphonies filled with rich, new information about how warped spacetime behaves when wildly vibrating,” Thorne wrote.

That time is nearly upon us, he now believes. The California Institute of Technology theorist writes in the August 3 issue of Science that in five years' time, ongoing upgrades to the world's leading gravitational-wave observatories will make those instruments sensitive enough to detect the waves, which would provide yet another confirmation of Einstein's general theory of relativity. The detection would also open up a new regime for studying black holes, those cosmic gluttons whose gravitational pull is so strong that it forms a one-way funnel into their maw.

As of now, astrophysicists can only infer the presence of a black hole by monitoring the environs around the putative object. In the case of Sagittarius A*, in the center of our own Milky Way galaxy, for instance, astronomers can see flares of radiation emanating from the black hole's location, caused by infalling material heating up and radiating outside the event horizon. Stars at the galactic center betray the presence of Sagittarius A* as well—their orbits point to the existence of a nearby compact object with the mass of four million suns.

The strong gravitational-wave signature expected from merging black holes would carry a wealth of information both about the objects involved and about their cataclysmic interaction.

Two major gravitational-wave detector projects have been on the lookout for these spacetime ripples, but so far the search has not produced any results. Both the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo observatory are L-shaped instruments with extremely long arms—four kilometers for the two LIGO facilities in Washington and Louisiana and three kilometers for Italy's Virgo. They rely on long-baseline interferometry, firing lasers down the perpendicular arms to see if one direction has been stretched or compressed relative to the other by a passing gravitational wave. “The advanced LIGO and advanced Virgo interferometers are now being installed and by 2017 should reach sensitivities at which black-hole mergers are observed,” Thorne writes. Sounds like the race is on to detect gravitational waves, one of the biggest prizes in physics.

Adapted from the Observations blog at blogs.ScientificAmerican.com/observations

COMMENT AT ScientificAmerican.com/oct2012

This article was originally published with the title Urge to Merge.

2 Comments

1. 1. vinodkumarsehgal 07:36 AM 9/22/12

   " In particular, the existence of gravitational waves—ripples in the fabric of space and time—might soon graduate from theoretical prediction to known fact."
   
   Gravitational waves are the theoretical predictions of Relativity. Relativity hypothesizes the continuous and smooth nature of space. If gravitational waves are the "ripples in fabric of space-time", it implies fabric of space-time should be composed of some physical stuff -- some building blocks, some atoms may be smaller than Plank Scale. Constitution of space with some particles shall invalidate the very nature of space namely continuous and smooth which forms the basis of Relativity. Hence a conundrum. If e.m waves can propagate thru vacuum without invoking any "fabric of space-time", why such need arises for gravitational waves provided such waves really exist.
   
   Recently, scientists have discovered a binary white dwarf system J-0651 located at a distance of only about 3000 light years away from earth. In J-0651, two white dwarfs are orbiting around each other at a very small distance of about less than 1/3rd of distance between earth and moon. Two white dwarfs are accelerating and their orbital periods also decreasing with each orbit. Scientist predict the creation of gravitational waves in J0651 system BUT none of the waves have been detected so far by any gravity detector. If gravity waves being generated at a distance of only 3000 light years have not been detected, could gravitational waves produced from colliding black holes located million and billion of light years away from earth be detected by any gravitational wave observatory, to whatever level they may be upgraded?

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2. 2. R.Blakely 06:29 AM 10/21/12

   We cannot find gravitationa waves because gravity noise is masking our sensors. I think photons emit gravitational waves. We are in a photon ocean, and thus in an ocean of noise.
   Tthe universe is not really expanding. Redshift is actually caused by an energy decrease as a photon travels thru space for billions of years. First, we must realize that a photon must have gravity since we know that gravity attracts photons. Second, as a photon travels thru space for billions of years, at the incredible speed of light, it must lose energy since it must emit gravitational waves. The energy loss appears as a redshift in photon color.

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