Galileo's Pendulum

The elliptical galaxy M87 is one of the largest in our local Universe, and it harbors a correspondingly massive black hole at its heart. Because of its relative closeness (“only” 54 million light-years distant) and low gas content to obscure its center, M87 is a wonderful natural laboratory for studying supermassive black holes. That its black hole is the source of a huge jet stretching about 5,000 light-years is a bonus. Contrast that with our Milky Way: the galactic center is shrouded in gas from our perspective, and the black hole is relatively quiet (i.e., boring).

Astronomers have also observed fluctuations in the jet from M87’s black hole over several years. One detailed study used the Very Long Baseline Array (VLBA), a string of 10 radio telescopes stretching across the United States and US Virgin Islands. Using many telescopes in tandem — a method known as very long baseline interferometry, or VLBI — allows for very high resolution images, much better than any single telescope can achieve. Taking successive images at three-week intervals, Craig Walker, Chun Ly, Bill Junor, and Phil Hardee created the movie you see below. Even on such a short time span as three weeks, the jet fluctuates in a noticeable way: this is a powerful black hole, pumping out a lot of energy into space.

I wrote about another VLBI observation of M87’s black hole using submillimeter light last fall, which determined the gas near the very center rotates in the same direction as the black hole. That’s an astounding discovery — I can still get excited about it nearly a year later. Now researchers using the Hubble Space Telescope have made a movie of the jet’s fluctuations in visible light. (Why the Hubble team absurdly decided to refer to this as a “slinky” is a question only they can answer.) Each of these measurements reveals more about the structure of the jet, which in turn tells us more about the black hole and environment at the center of M87.

I’ll be teaching a class on black holes for CosmoAcademy this fall, in which I hope you’ll consider enrolling. Black holes are agents of cosmic destruction: they shred stars, crush planets, and through their gravitation pump huge amounts of strong radiation into their environments. From a remove, however, they are also agents of beauty: the light emitted by their action makes them some of the brightest objects in the cosmos, visible across the deep void of space. That coupling of violence and wonder is why I love black holes; I hope you can see why they are wonderful too.