As I continue to ponder the spooky character of quantum physics (the 10^-n reality), this May 17, 2017, Space.com article addresses a question at the other end of the cosmic scale (the 10^n reality): How Many Stars Are In The Universe?
So how do astronomers figure out how many stars are in the universe? The first sticky part is trying to define what “universe” means, said David Kornreich, an assistant professor at Ithaca College in New York State. He was the founder of the “Ask An Astronomer” service at Cornell University.
Do a rough back-of-the-envelope calculation (or use the “back of a napkin”) — simple, yes?
- Consider the current model of the observable universe (which “appears to go back in time by about 13.7 billion light-years”).
- Estimate the number of galaxies.
- Estimate the average number of stars in a galaxy.
But each one of those factors is tricky, as discussed in the article. Regardless, even being conservative results in a mind boggling number.
Kornreich used a very rough estimate of 10 trillion galaxies in the universe. Multiplying that by the Milky Way’s estimated 100 billion stars results in a large number indeed: 1,000,000,000,000,000,000,000,000 stars, or a “1” with 24 zeros after it. Kornreich emphasized that number is likely a gross underestimation, as more detailed looks at the universe will show even more galaxies.
So, survey says? Sky surveys are interesting.
Recent estimates of the number of galaxies in the observable universe range from 200 billion (2×1011) to 2 trillion (2×1012) or more, containing more stars than all the grains of sand on planet Earth.