How Many Stars Are There?
Whenever we look up at the clear night sky, we can see a lot of stars. From here on Earth, if you happen to be in an area without light pollution, you can see over 10,000 individual stars. That may seem like a lot, but it represents less than 1% of all stars in our galaxy alone. The Milky Way is home to about 100 billion stars, and the Milky Way itself is just one of trillions of potentially other galaxies. Is it possible to estimate the number of stars in the universe?
Estimating the Number of Stars
If you try to count the stars one by one, it won’t take you long to lose track. Even if you try to count all the stars in the Milky Way, it will take years before you are done. Counting the number of stars in the universe would take millions upon millions of years, so counting them individually would be completely impossible. Instead, astronomers found a way to estimate the number of stars. Since most stars are in galaxies, estimating the number of galaxies in the universe is a good first step in estimating the number of stars in the universe. However, estimates of the number of galaxies vary significantly, and range from as low as 100 billion to as high as 10 trillion. In 2016, a study of Hubble images gave an estimate of two trillion galaxies, which is generally the number used to estimate the number of stars. Furthermore, astronomers assumed that the Milky Way is a fairly typical galaxy, and the number of stars it contains is the average number of stars contained in a given galaxy. With 100 billion stars in the Milky Way and two trillion galaxies in the observable universe, we simply multiply 100 billion by two trillion. Thus, the number of stars in the universe is estimated at 200 billion trillion. To get an idea of how big that number is, here’s the whole thing: 200,000,000,000,000,000,000,000,000.00.
Problem With Estimate
There are some real problems with estimating the number of stars in the universe. First, we can only estimate the number of stars in the observable universe. The universe itself extends far beyond what we can actually see, and beyond our cosmic horizon, there may be more galaxies and more stars. When we estimate the number of stars in the universe, it represents only the region of the universe that we can physically see. Furthermore, the universe could be infinitely large, in which case there could be an infinite number of stars throughout the cosmos.
The second problem is the assumption that the Milky Way is a typical galaxy. Galaxies vary widely in the number of stars they contain, with some containing far fewer stars than the Milky Way and some containing much more. Also, the number of stars in the Milky Way is estimated based on the mass of our galaxy, which is about 100 billion solar masses. This means that the total number of stars in the Milky Way is equivalent to 100 billion solar masses. If our galaxy only contained stars like the sun, it would contain 100 billion stars. However, most stars are low-mass stars called red dwarfs, so the number of stars in our galaxy likely exceeds 100 billion.
A third problem is the fact that the number of galaxies in the observable universe is currently unknown, and the number two trillion is likely very small. There are possibly trillions of more galaxies in the observable universe. When we take all of this into account, the actual number of stars likely far exceeds the estimated 200 billion trillion.
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