universe - Are black holes expanding?

Simple Answer

Large black holes are usually expanding by an incredibly small amount as they suck in more stuff (gases, planets, stars, etc.) through gravity. So they are expanding but not because of our expanding universe.

Exceptions

According to Wikipedia, small black holes might shrink. Stephen Hawking predicts that all black holes have radiation. Small black holes, that suck in less, might emit more energy than they pull in, so they theoretically shrink and close.

Big Asterisk

There are many additional details that could be included in this thread. I think the most important to point out is that fifty years ago black holes were still largely science fiction. So it's a relatively new science. And even if we had been studying them for 200-300 years, they're hard to observe and practically impossible to experiment with. Point being, most black hole knowledge is actually black hole theory.

Observing Black Holes

Here's a relevant Wiki excerpt:

In June 2008, NASA launched the Fermi space telescope, which is
searching for the terminal gamma-ray flashes expected from evaporating
primordial black holes. In the event that speculative large extra
dimension theories are correct, CERN's Large Hadron Collider may be
able to create micro black holes and observe their
evaporation.

Relevant Detail on Black Holes

Black holes were once massive stars. Stars have massive gravity but they don't collapse until they run out of fuel. When they do run out of fuel, they expand then collapse. Big stars have so much gravity that they collapse into a small sphere with gravity so intense that light can't escape it. That is when a black "hole" is born. Really, it's more like a black sphere. It appears to be a hole only because no light escapes. Inside the sphere there could be a hole, but no one knows.

Further Explanation on Black Hole Expansion

Bigger stars have more mass so when they collapse, they have more gravity and the perceived "hole" is bigger. Typically, large galaxies have large black holes at their center and small galaxies have small black holes. Over time, the black hole will pull more matter (gases, planets, asteroids, etc.) into its sphere of blackness. This adds to its mass and slowly increases its gravity. More gravity means a wider radius of black where from which not even light escapes.

Unanswered / Theorized

When does a black hole stop growing and why? That's hard to answer because we have no data about the inside of a black hole. Some people theorize the immense gravity bends space/time to create a wormhole. Many questions about space are being answered in our lifetime by observing and experimenting. Black holes are hard to observe and even harder to experiment with. Most "answers" in our lifetime will be more theory than proven physics.