How many galaxies are in the Universe?
The number of galaxies in the universe is unknown, but it is thought to be somewhere between hundreds of billions and two trillion.
In one study in 2016, astronomers examined the Hubble eXtreme Deep Field (XDF) - a small patch of sky imaged very deeply in ultraviolet, visible and infrared light - and a total of approximately 5,500 galaxies were found. If you scale this number by the number of such images it would take to cover the entire sky, you find that there would be about 176 billion galaxies visible in observations like these. However this is only a lower limit on the number of galaxies in the universe as there may be even more that are too small, too faint, too distant and/or are hidden behind gas and dust. Astronomers used computer simulations to both try and match what is seen with telescopes, and estimate how many more galaxies there may be. In this way they came up with the estimate of two trillion.
A more recent study in 2021 used data from NASA's New Horizon's spacecraft to measure the total light seen in seven patches of sky. According to their analysis, the total number of galaxies contributing to this light is more likely in the hundreds of billions, rather than trillions.
Estimates of the total number of galaxies will continue to be refined as more powerful telescopes study the universe. NASA's JWST observatory, launched December 25, 2021, will be able see even further back and image smaller and fainter distant galaxies. This will lead to a new estimate. Whatever the final number may be, it is worth noting that it will be incredibly large! There are a few hundred billion stars in our Milky Way galaxy so there’s at least one galaxy in the universe for every star in the Milky Way. It's a big universe...