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How many clusters are there in the observable universe?

Answer 1

About 25 Billion .

Be cautious with your definition of a cluster though; based on the context, I assume you are asking about galaxy clusters. Scientists have confirmed that they have observed 25 billion galaxy clusters. This is not to be confused with globular clusters or open clusters.

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Answer 2

Christopher Ales

The exact number of clusters in the observable universe is unknown, but estimates suggest there are tens of millions to hundreds of millions of galaxy clusters.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.