There’s no upper limit to how massive galaxies or black holes can be, but the most massive known star is only ~260 solar masses. Here’s why.
Here in our Universe, the most limiting factor behind the largest structures we see is time. Shortly after the Big Bang, there were no stars, galaxies, or black holes: objects that require significant amounts of mass to accumulate in one place. The Universe, even though it was born with density imperfections on all cosmic scales, only allows signals — even gravitational signals — to propagate through its space at a finite, limited speed: the speed of light. As a result, it takes a long period of time for enough mass to accumulate in order for these structures to emerge:
- tens to hundreds of millions of years for stars and black holes,
- hundreds of millions of years for galaxies,
- around a billion years for galaxy clusters,
- and several billions of years for the filamentary cosmic web.
Now that some 13.8 billion years have passed, we can see what the largest, most massive examples of these different types of objects are. Black holes range from about three solar masses up to tens of billions of…
