The universe sings to us in gravitational waves, and we're starting to listen. Michelle Thaller discusses the discovery of gravitational waves and their unusual effects in her latest astronomy podcast.



Surely one of the most profoundly wonderful and strange ideas in modern physics is that empty space, coupled with time itself, is a thing that can be bent and stretched, and even made to ripple like waves on a pond.

More than 100 years ago, Albert Einstein described gravity as a bending of space and time; anything with mass, from an electron to a supermassive black hole, can bend the universe around it, distorting the measurements of our rulers and clocks in the process. And if this mass happens to move around, spacetime responds to that motion, creating waves of gravity. Incredibly, we exist in a matrix of constantly bending and rippling spacetime.

Luckily for us, it takes a huge amount of energy to generate even a tiny distortion, compared to our human scale. These waves are so small that our most advanced detection devices have just barely been able to tease out signals from one of the most violent events the universe has to offer: two merging, massive black holes. In September 2015, twin detectors that make up the Laser Interferometric Gravitational Wave Observatory (LIGO) shook slightly as the waves from a black hole merger 1.3 billion light-years away reached Earth. This event was the first confirmed detection of a gravitational wave, and by the time it passed us by, the ripple was many, many times smaller than the diameter of a single proton. But that was enough for LIGO.

In this episode of Orbital Path, Professor Jana Levin, a theoretical physicist at Columbia University, tells us the remarkable story about how LIGO came to catch those elusive waves for the first time, turning new eyes, or more accurately, new ears, on to the sound of the universe itself.

If we indeed live in a rippling and undulating universe, are there consequences of gravitational waves we can see, even if the waves themselves were not detected? Marco Chiaberge (STScI) thinks he may have seen just that. Using the Hubble Space Telescope, Chiaberge found a very strange galaxy that appears to be hurling a supermassive black hole out of its core.

Bright, active galaxies are usually powered by black holes millions or billions of times the mass of the Sun in their cores, probably the end result of many smaller black holes colliding and merging over huge timescales. It would make sense, then, that these hugely massive objects would rest right in the center, at the center of mass of their galaxies, everything else spinning around them. But in this case, a black hole with the mass of a billion Suns has been sent careening out of its galaxy at over 4 million mph. Can we all just pause for a moment and consider that? What could possibly have the energy to accelerate a billion solar masses to such immense speeds?

Chiaberge thinks gravitational waves might be the answer. If two huge black holes merge in some rare and unbalanced say, the resulting waves might have gone off asymmetrically, like a bullet fired out of a gun. And the black hole got kicked hard by the recoil.

How else do gravitational waves influence the universe around us? What sorts of exotic objects will we find with the next generation of gravitational wave observatories? We have hardly any idea yet. The universe has been singing to us all along, but only in the last two years have we opened our ears to listen.

Orbital Path is produced by PRX and supported by the Alfred P. Sloan Foundation. Don't miss PRX's other science podcasts: Transistor and Outside Magazine.