SpaghettaBlack Hole Physics / Spaghettification Stretch

Spaghetta does not pull you in. She pulls your feet harder than your head, and that is worse.

Gravity weakens with distance, so near a heavy object the near end of anything is pulled more strongly than the far end. The difference is the tidal acceleration, the first formula on this page: it grows with the mass, with the length of the body, and very steeply, as one over the cube of the distance. Ordinary tides on Earth's oceans are the same effect, from the Moon. Near a black hole, it becomes the stretching astronomers call spaghettification: pulled long along the line toward the hole, squeezed in from the sides.

The second formula, the Schwarzschild radius, sets the size of the event horizon: about 3 kilometres for each solar mass. Now the surprise. Take a black hole of ten solar masses, with a horizon radius of about 30 kilometres. At the horizon, the difference in pull between the head and feet of a two-metre person is about twenty million times Earth's gravity. You would be torn apart long before reaching it.

Take instead the black hole at the centre of our galaxy, about four million solar masses. Its horizon is so large that the tidal stretch there is around a ten-thousandth of Earth's gravity. You would cross the horizon without feeling a thing. Spaghettification would still come, but later, deeper in. The bigger the black hole, the gentler its edge.

Astronomers watch this happen to whole stars. When a star wanders too close to a supermassive black hole, tides tear it apart and part of its gas falls in, flaring for months. Such tidal disruption events are now routinely observed.

Spaghetta is not cruel. She is just steeper than you.