Gravity waves from black holes

Image: Genze/NASA

More than a thousand million years before dinosaurs roamed Earth, a ripple in space was spreading through the universe. Traveling at 300,000 kilometers per second, the speed of light, it had covered 95 percent of its journey to Earth when the dinosaurs became extinct.

Spreading in all directions and so getting weaker all the time, it swept past Earth on Sept. 14, 2015. For a tiny fraction of a second, as it passed through us all, we were stretched in one direction and squashed in the other direction and then the reverse, like wobbling jelly.

But the only people who noticed were scientists, who found that 4 kilometer-long laser beams were stretched and squashed by less than a hundred-millionth the size of an atom. The tiny wiggle was detected in Louisiana and a few milliseconds later in Washington state as the ripple in space swept past and continued on its way through the universe. These incredibly sensitive detectors are called Advanced LIGO, for Laser Interferometer Gravitational-wave Observatory.

Most astronomical observatories study light from stars, or radio or other electromagnetic waves. Now we have opened new “eyes” on the sky, not so much seeing as feeling the ripples in space (strictly speaking, in space-time) called gravity waves, from the most cataclysmic events since the Big Bang 13.7 billion years ago.

Einstein’s theory of gravity, known as the theory of general relativity, predicted the existence of these waves a hundred years ago. He did not think they could ever be detected. But then again, he had no idea of the advances we would make in technology. His theory also predicted that stars more massive than the sun could collapse under their own gravity to form black holes, a few kilometers across, with gravity so strong than nothing can escape.

The ripple in space-time that LIGO detected was caused by two black holes, 20 to 30 times the sun’s mass, spiraling around and crashing into each other.  The energy emitted was momentarily more than that of all the stars in all the galaxies in the visible universe.

Since that first detection, probably to be rewarded with this year’s Nobel physics prize, more black hole mergers have been detected, and as more gravity-wave observatories open their “eyes,” our focus, now fuzzy, will sharpen.

Shakespeare wrote, “There are more things in Heaven and Earth, Horatio, than are dreamt of in your philosophy.” Right again, Will.

This is a version of an article that first appeared in Positively Naperville.