If Spaans is right, black holes grow by feeding on spacetime itself and their quantum feeding habits effectively solve the problem of how the biggest black holes become so massive, so quickly. “Supermassive black holes can acquire a lot of their mass through these quantum contributions over the life time of the universe,” he says.

Here’s some useful background. In 1955, the American theoretical physicist John Wheeler suggested that at very small length scales, virtual particles, including quantum black holes, must constantly jump in and out of existence creating a kind of foamy structure that is very different from the smooth spacetime we see at larger scales.

Nobody has ever observed quantum foam but there is widespread agreement that the fabric of the universe must be made of something like it.

In ordinary circumstances, quantum foam has little impact. However, physicists think it must play an important role in the most extreme circumstances where the universe is being torn apart by the forces acting on it. Black holes are clearly one of these places.

Spaans’ approach is to ask what happens when a black hole meets quantum foam. The answer is straightforward. “Quantum ﬂuctuations in the form of mini black holes can couple to macroscopic black holes and allow the latter to grow exponentially,” he concludes.

He says this kind of growth can easily account for the observed size of relatively young supermassive black holes. And he goes on to predict that this mechanism could allow smaller black holes to grow too. In fact, he suggests these smaller objects, which would be difficult to observe from Earth, could make up a significant fraction of the mysterious dark matter that astronomers believe the universe must contain.

That’s interesting stuff but new ideas are worth little unless they make experimentally testable predictions and Spaans does not disappoint in this respect. He says that this quantum feeding mechanism must apply to the supermassive black hole at the centre of our galaxy and that consequently, it must be growing at the rate of about 10^-3 solar masses per year.

And that ought to be measurable. Spaans says that signals produced by pulsars are particularly sensitive to their local gravitational conditions. So it should be possible to spot the the increasing gravitational field of a growing black hole by studying pulsars that orbit close by.

He points just such a pulsar was discovered earlier this year at the centre of our galaxy and that a long-time monitoring program of its behavior is now in order.

Such a program would take years or even decades to reveal the kind of changes that Spaans predicts. But when it comes to the feeding habits of black holes, knowing what’s on the menu could be priceless information.

Ref:arxiv.org/abs/1309.1067: On Quantum Contributions to Black Hole Growth