SKY FULL OF STARS

By: Karl Putz

“There wouldn’t be a sky full of stars if we were all meant to wish on the same one.” – Frances Clark

There is a lot of news recently about new planets, and the number of them that might be able to harbor life, based on the number of stars and how many of them have planets in the “habitable zone“. In reading about these values, I wondered a really simple question. What is the star creation rate of the universe? In other words, how many stars are born every second in the entire universe? Take a moment and guess. 1,000? 1? 0.001? Even the last value has a star popping into existence every 17 minutes or so, which seems pretty fast to me.

Luckily, we don’t have to guess. The universe is 13.8 billion years old. A year is 31.5 million seconds long. The best estimates for the number of galaxies in the universe is 170 billion. The number of stars per galaxy is 400 billion. So that means the universe has been around for 4*10^17 seconds (a 4 followed by 17 zeros) and contains 7*10^22 stars (7 followed by 22 zeros). If we simply divide the number of stars by the number of seconds we get 156,000 stars created, on average, every single second the universe has existed. That blew my mind.

It means that every night (~12 hours) the universe creates enough stars for each of us (all 7 billion) to wish on our very own.