A scientist asks: Can a black hole fill up?

thisThe article was first published on forcing

Black holes don’t work like a vacuum cleaner that’s always on. And it’s not like a drain in a bathtub or a gluttonous hole in the floor.

But we resort to analogies with something we know when we think about and explain black holes.

Space is beyond our imagination, so understanding something as complex and compact as a black hole can be a challenge.

But that doesn’t mean we shouldn’t try. So, a reader of videnskab.dk Henning wrote to us in the hope of finding out if black holes are really insatiable.

Can a black hole continue to attract matter? Will it not be filled in the end or where will the materials end up? he writes in an email.

To investigate what happens to whatever a black hole attracts, we spoke to Albert Sneben, a doctoral student at the Niels Bohr Institute at the University of Copenhagen.

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He has already solved one of astrophysics’ biggest mysteries about black holes.

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Here, the artist has envisioned a black hole that looks more like a ball than a wormhole. Image: XMM Newton/ESA/NASA

Bullet…black?

First, we must correct the misunderstanding. A black hole is not a hole, but it is shaped like a ball.

The name of this phenomenon probably arose because what ends up in a black hole cannot escape back.

But the question is whether a black hole can really continue to attract matter without any limits.

– Yes, it can, is the short version of Albert Snippen’s answer.

– If you pour cement into a hole, it will eventually fill it up, but a black hole can always attract more material, he explains.

The black hole will gain more and more mass, more gravity, and grow larger.

A bit like an exchange

If matter has been captured by a black hole, the first stop is the so-called accretion disk. Imagine a rotating disk around a black hole, which is spherical.

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When matter is in an accretion disk, many collisions occur. Then the substance heats up and starts to glow.

Matter on its way to the black hole shines brightly, and that light can slow down the process, Sneppen explains.

Does your mind start to get a little fuzzy when you try to imagine it? Fortunately, Sneppen has a metaphor that can help.

– The concept might be a little complicated, but it’s really just about if all of this ends up in the drain in the bathtub, it’s going to be pressed very tightly together and then it’s going to be very bright. This, he explains, makes it difficult for other materials to come down at the same time.

hole in physics

But what happens to everything that ends up in a black hole?

The short answer is we really don’t know.

– It’s almost a philosophical question, because there is the idea that when something falls into a black hole, we lose all contact with the world in which it falls, says Snippen.

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Once matter passes what is called the event horizon, the boundary between the black hole and the outside world, we have no idea what happens to it.

You may have heard that everything in a black hole is squeezed together by gravity? That might be the case, but the researchers don’t know.

Because gravity is so strong that not even light can escape, we’ll never be able to see or measure what’s going on there.

Even if we sacrifice ourselves and take a one-way trip to a black hole, we won’t be able to see it, because there is no way to send the information back.

However, physicists have modeled what such a scenario might look like. They do this by taking the physical laws we know from Earth and adapting them to space.

For example, Einstein’s gravitational equations. If it applied to black holes, it would mean that the material there would forever fall towards a tiny point.

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Albert Snippen does not want to guess:

– What happens when you take us, us suns and stars and mass and put them together in a very small space, is itself indefinite and completely incomprehensible, he says and takes what is by definition an unanswerable question.