Tilt a Black Hole and Watch What Happens

A new simulation published in yesterday's Science shows how black holes govern their surroundings.

Black hole tilt
A new simulation shows how a black hole dominates its surroundings.
Ralf Kaeler (KIPAC) and Jonathan McKinney (UMD)
Black holes are simple creatures. No matter what they gobble down, be it a star, a gas cloud, or the kitchen sink, they can still only be described by two* properties: mass and spin. But these simple creatures live in complex worlds. The matter they feed on creates a complicated “atmosphere” of hot, swirling gas and crackling magnetic fields. A study published in yesterday’s Science shows just how a spinning black hole interacts with its tangled surroundings, and its (totally cool) video is below.

Theorist Jonathan McKinney (Stanford University and University of Maryland) and his colleagues ran a three-dimensional simulation that takes all the complexity of spacetime curvature and magnetic fields into account. With the physics in place, their goal was to watch what happens to a black hole’s neighborhood when the spinning black hole tilts on its side.

In a normal, feeding black hole, the gas and occasional torn-up star that make up a black hole’s diet swirl into a disk before falling into the gaping hole. Two jets fly out at relativistic speeds along the black hole’s poles, created by the interaction between the disk’s magnetic field and the black hole’s spin. The end result looks like a spinning top with a thick central disk; the top’s long handle and spindle represent the relativistic jets.

But what happens when gas suddenly comes from a new source such as a stray gas cloud? From another perspective, it’s as though the spinning black hole suddenly tilts on its side. Does our spinning top come apart, or does the black hole somehow manage to drag the disk and jets back into alignment?

The answer is in the video below. In the first half, the black hole contentedly feeds on matter, surrounding itself with a thick, swirling disk (yellow). Two jets (blue) shoot out along the black hole’s poles. At 0:30, the black hole tilts. Suddenly the two jets disappear, then appear again along the black hole’s new spin axis. As the jets ram into the gas disk, they force the disk to align along the new spin axis, too. Black holes may be simple, but they’re powerful too and ultimately, they dominate their surroundings.

*Hypothetically, they could have charge too, but black holes remain neutral, gobbling negative charge along with the positive.

2 thoughts on “Tilt a Black Hole and Watch What Happens

  1. Monica YoungMonica Young

    That’s a great question, Charles! Jonathan McKinney, the lead author of the Science article, says that the total time of the simulation would scale with the mass of the black hole. So for example, if you had a stellar mass black hole, like say GRS 1915+105, weighing about 10 Suns, the simulation covers 2 seconds. For a black hole with the mass of 4 million Suns, such as Milky Way’s central black hole (known to astronomers as Sgr A*), the time scale would be 7 days. And for a truly massive black hole such as the one lurking in M87, which weighs 6 billion Suns, the simulation covers 28 years.

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