Question: How many black holes are there?

Ry Cutter answered on 22 Jun 2020:

We don’t really know!

The problem is, black holes are ‘electromagnetically’ silent. They don’t emit light. The only way we know a black hole is in a place is by looking at how light and other stars act as they pass by the black hole. We can make estimates on the numbers of black holes using statistics though! Let’s define the three types of black hole.
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1.) Supper massive black holes (SMBH): These are HUGE black holes, millions of times heavier than our sun, found in the center of galaxies. We think there are about 100 billion – 1 trillion galaxies in the universe; so, we expect there to be about that many SMBHs
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2.) Stellar mass black holes. As the name suggest they weigh similar amounts to stars. Again, these guys are elusive, we can’t see most of them. So, using the ones we can see in combination with the amount of stars that can become black holes, we estimate there are roughly 10 million – 1 billion stellar mass black holes in the Milky Way… Now assuming our galaxy (the milky way) isn’t special, that means we can multiply the number of galaxies by the number of black holes in our galaxy. oof, that’s a big number! We can say there are between:

1,000,000,000,000,000,000 (18 zeros) and 1,000,000,000,000,000,000,000 (21 zeros)
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3.) The third type of black hole is called a primordial black hole. These are theoretical, so we haven’t actually seen any or know if they are real, but I think they’re cool! They were made at the beginning of the universe when everything was chaotic, so chaotic that gravitational collapse could just happen! There probably aren’t enough to make a dent in the massive numbers we’ve already found though.
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Great Question, I had a lot of fun answering it 😀

Ry