Question: Which way must a dumbbell fall to radiate gravitational waves?
About the article "Gravitational wave", section "Sources of gravitational waves".

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In general terms, gravitational waves are radiated by objects whose motion involves acceleration, provided that the motion is not perfectly spherically symmetric (like an expanding or contracting sphere) or cylindrically symmetric (like a spinning disk or sphere).
A simple example of this principle is provided by the spinning dumbbell.
If the dumbbell spins like wheels on an axle, it will not radiate gravitational waves; if it tumbles end over end like two planets orbiting each other, it will radiate gravitational waves.
The heavier the dumbbell, and the faster it tumbles, the greater is the gravitational radiation it will give off.
If we imagine an extreme case in which the two weights of the dumbbell are massive stars like neutron stars or black holes, orbiting each other quickly, then significant amounts of gravitational radiation would be given off.
Some more detailed examples:
Two objects orbiting each other in a quasi-Keplerian planar orbit (basically, as a planet would orbit the Sun) will radiate.
 A spinning non-axisymmetric planetoid — say with a large bump or dimple on the equator — will radiate.
 A supernova will radiate except in the unlikely event that the explosion is perfectly symmetric.
 An isolated non-spinning solid object moving at a constant velocity will not radiate.
This can be regarded as a consequence of the principle of conservation of linear momentum.
 A spinning disk will not radiate.
This can be regarded as a consequence of the principle of conservation of angular momentum.
However, it "will" show gravitomagnetic effects.
 A spherically pulsating spherical star (non-zero monopole moment or mass, but zero quadrupole moment) will not radiate, in agreement with Birkhoff's theorem.
More technically, the third time derivative of the quadrupole moment (or the "l"-th time derivative of the "l"-th multipole moment) of an isolated system's stress–energy tensor must be nonzero in order for it to emit gravitational radiation.
This is analogous to the changing dipole moment of charge or current necessary for electromagnetic radiation.
Radiate may refer to:  Radiation, a process by which energetic particles or energetic waves travel  Radiate (coin), an ancient Roman bronze coin  Radiate crown, headgear symbolizing the sun  
A gravitational-wave detector is any device designed to measure gravitational waves, tiny distortions of spacetime that are predicted by Einstein's theory of general relativity.
The existence of gravitational radiation is a prediction of general relativity.
Gravitational waves are perturbations in the curvature of spacetime caused by accelerated masses.
Since the 1960s gravitational-wave detectors have been built and constantly improved.
The present-day generation of resonant mass antennas and laser interferometers has reached the necessary sensitivity to detect gravitational waves from sources in the Milky Way.
As of early 2014, no direct detection of gravitational waves has yet been accomplished, although a number of experiments have now added to the evidence that gravitational waves are more than mathematical anomalies of relativity calculations (ref.
the 1993 Nobel Prize in Physics).
On 17 March 2014, astronomers at the Harvard-Smithsonian Center for Astrophysics announced the apparent detection of gravitational waves, which, if confirmed, may provide strong evidence for inflation and the Big Bang. 
One of several analogies between weak-field gravity and electromagnetism is that, analogous to electromagnetic waves, there are gravitational waves: ripples in the metric of spacetime that propagate at the speed of light.
The simplest type of such a wave can be visualized by its action on a ring of freely floating particles.
A sine wave propagating through such a ring towards the reader distorts the ring in a characteristic, rhythmic fashion (animated image to the right).
Since Einstein's equations are non-linear, arbitrarily strong gravitational waves do not obey linear superposition, making their description difficult.
However, for weak fields, a linear approximation can be made.
Such linearized gravitational waves are sufficiently accurate to describe the exceedingly weak waves that are expected to arrive here on Earth from far-off cosmic events, which typically result in relative distances increasing and decreasing by formula_8 or less.
Data-analysis methods routinely make use of the fact that these linearized waves can be Fourier decomposed.
Some exact solutions describe gravitational waves without any approximation, e.g., a wave train traveling through empty space or so-called Gowdy universes, varieties of an expanding cosmos filled with gravitational waves.
But for gravitational waves produced in astrophysically relevant situations, such as the merger of two black holes, numerical methods are presently the only way to construct appropriate models. 
Livingston Parish is home of one of two installations for a gravitational wave observatory (LIGO) which is a facility dedicated to the detection of cosmic gravitational waves and the harnessing of these waves for scientific research.