How Many Stars?
Written by Fraser Cain
It's a great big Universe out there, with a huge numbers of stars. But how many stars are there, exactly? How many stars are there in the Universe? Of course it's a difficult question to answer, because the Universe is a vast place and our telescopes can't reach every corner to count the number of stars. But we can make some rough estimates.
Almost all the stars in the Universe are collected together into galaxies. They can be small dwarf galaxies, with just 10 million or so stars, or they can be monstrous irregular galaxies with 10 trillion stars or more. Our own Milky Way galaxy seems to contain about 200 billion stars; and we're actually about average number of stars.
So an average galaxy contains between 1011 and 1012 stars. In other words, galaxies, on average have between 100 billion and 1 trillion numbers of stars.
Now, how many galaxies are there? Astronomers estimate that there are approximately 100 billion to 1 trillion galaxies in the Universe. So if you multiply those two numbers together, you get between 1022 and 1024 stars in the Universe. How many stars? There are between 10 sextillion and 1 septillion stars in the Universe. That's a large number of stars.
Of course, the estimates for how many stars there are is still very rough and will need fine tuning. Space agencies are planning to launch new spacecraft to help revise the estimates for how many stars there are in the Universe. ESA's Herschel spacecraft, due for launch in 2009 will look back into the early Universe to calculate the rate of star formation billions of years ago. And this will help astronomers estimate how many stars there are.
We have written many articles about stars on Universe Today. Here's an article about how many stars there are in the Milky Way. And here's an article about the largest structure in the Universe.
Want more information on stars? Here's NASA's World Book on Stars, and more information from NASA's imagine the Universe.
We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?
Filed under: Astronomy
