" A large number of 'rogue' supermassive black holes are wandering the universe." Are they like landmines?

No, they are not like landmines.  They aren't all black either, rather the gravity beyond the event horizon is so strong that not even light can escape (or time).  Matter at or nearing the event horizon still emits light.

Remember, we don't know a lot about black holes.  It wasn't until recently the we even "saw" one.  I think that as we continue to study black holes, we'll come to find that they're an essential component to the universe (much like hurricanes are on earth).   It's Quite possible that black holes actually throw matter back out into space.  Like a giant recycler.  ??  

Apparently there are two types of "black holes":
i) Countless black holes that are the remnants of massive stars.
ii) Supermassive black holes that lie at the center of virtually all large galaxies.
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"[...] black holes [...] appear to exist on two radically different size scales. On the one end, there are the countless black holes that are the remnants of massive stars. Peppered throughout the Universe, these "stellar mass" black holes are generally 10 to 24 times as massive as the Sun. Astronomers spot them when another star draws near enough for some of the matter surrounding it to be snared by the black hole's gravity, churning out x-rays in the process. Most stellar black holes, however, are very difficult to detect. Judging from the number of stars large enough to produce such black holes, however, scientists estimate that there are as many as ten million to a billion such black holes in the Milky Way alone.

On the other end of the size spectrum are the giants known as "supermassive" black holes, which are millions, if not billions, of times as massive as the Sun. Astronomers believe that supermassive black holes lie at the center of virtually all large galaxies, even our own Milky Way. Astronomers can detect them by watching for their effects on nearby stars and gas. [...]

Historically, astronomers have long believed that no mid-sized black holes exist.  However, recent evidence from Chandra, XMM-Newton and Hubble strengthens the case that mid-size black holes do exist. One possible mechanism for the formation of supermassive black holes involves a chain reaction of collisions of stars in compact star clusters that results in the buildup of extremely massive stars, which then collapse to form intermediate-mass black holes. The star clusters then sink to the center of the galaxy, where the intermediate-mass black holes merge to form a supermassive black hole."

Extract source:
https://science.nasa.gov/astrophysics/focus-areas/black-holes

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What is a "black hole"?
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"A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying.

Because no light can get out, people can't see black holes. They are invisible. Space telescopes with special tools can help find black holes. The special tools can see how stars that are very close to black holes act differently than other stars. [...]

How Do Black Holes Form?

Scientists think the smallest black holes formed when the universe began.

Stellar black holes are made when the center of a very big star falls in upon itself, or collapses. When this happens, it causes a supernova. A supernova is an exploding star that blasts part of the star into space.

Scientists think supermassive black holes were made at the same time as the galaxy they are in.

If Black Holes Are "Black," How Do Scientists Know They Are There?

A black hole can not be seen because strong gravity pulls all of the light into the middle of the black hole. But scientists can see how the strong gravity affects the stars and gas around the black hole. Scientists can study stars to find out if they are flying around, or orbiting, a black hole.

When a black hole and a star are close together, high-energy light is made. This kind of light can not be seen with human eyes. Scientists use satellites and telescopes in space to see the high-energy light."

Extract source:
https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html

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This post was edited by Robert at August 25, 2021 2:49 AM MDT