Galileo's Pendulum

Black holes sing in harmony with themselves. The “notes” are flashes of light rather than sound, but black holes born from the death of very massive stars emit bursts as hot matter orbits close to the event horizon. That’s a natural consequence of the in-and-out motion of high-energy particle motion as strong gravity whips them up close to light-speed. As a result, the frequency of the bursts depends on the mass of the black hole, meaning we can work backward from the timing of the flashes to determine how big the black hole is.

Now some astronomers have done the same for an intermediate mass black hole (IMBH) in the galaxy M82, which lies between the stellar-mass objects like Cygnus X-1 and the huge supermassive black holes at the centers of most galaxies. The evidence for the existence of IMBHs has often been ambiguous, though: other researchers have argued the black hole in M82 is stellar-mass. However, if the song of the black hole is to be believed, it’s about 400 times the mass of the Sun — too big to be stellar-mass, but far too small to be supermassive.

For low-mass black holes, the pattern is the juxtaposition of two evenly-timed bursts of light with three flares in the same time interval. Music aficionados recognize this rhythm as a triplet or “hemiola”: the playing of two different musical patterns simultaneously. Another musical metaphor: if we interpret the frequencies as notes instead of rhythms, the ratio of 3 to 2 is known as a “perfect fifth” in harmony, the foundation of any number of chords. Low-mass black holes “sing” in harmony with themselves, though with flashes of light instead of sound.

Do middleweight black holes do the same? [Read more…]

Speaking of black holes! I am teaching a new class on some of the wilder aspects of black hole science next month: black hole thermodynamics, quantum gravitational aspects of the event horizon, Hawking radiation, the holographic principle, firewalls, and the like. Sign up today!