Don't objects steadily evaporate over time by emitting gravity waves?

No, because this process is so inefficient.

Although the mass of every body includes the energy stored in its gravitational field, the only way to get a body to loose energy by gravity is by way of gravitational radiation.

General Relativity theory says that gravity waves and radiation are produced by accelerating the body. However, in order for a body to lose mass this way, you need to accelerate the body enormously because gravity waves are so weak.

The acceleration felt by two dense neutron stars orbiting around each other every minute at a distance of a few hundred kilometers is the most extreme acceleration known. It is not very effective in causing the bodies to loose much mass compared to the feeble mass lost by the electromagnetic radiation leaving their surfaces.

For example, our sun emits 4x10^33 ergs/sec of electromagnetic energy. From E=mc^2 this is equal to a mass loss of 4x10^33/(3x10^10)^2 = 4.4 million metric tons of mass every second. During its 4.5 billion years of life, it has lost 6.2x10^23 metric tons of mass...but its physical mass consists of 2x10^27 metric tons, so it has only lost 0.003 of its mass by radiation.

Gravity is even less efficient than this because the sun is only weakly being accelerated by its planets and the rest of the stars in the Milky Way.

Return to Dr. Odenwald's Gravity page at the Astronomy Cafe Blog.