How do scientists estimate the number of stars in the universe?

Question

Asher Cohen · Accepted Answer

Usually by estimating the number of stars in our own galaxy first (around 100 billion) and then estimating the number of galaxies.

There is a lot of estimating that goes in this process. First, an estimate of the number of stars in our part of the galaxy is made.

Then extrapolate this to the rest of the galaxy - current estimate around 100 billion for the Milky way galaxy, but this changes when new information becomes available. Then, estimate the number of galaxies in the known universe and multiple by the average estimated stars in a single galaxy.

But the estimate of the number of galaxies in the universe has changed dramatically with the Hubble space telescope that discovered thousands of galaxies in a region of space that looked fairly dark (see pic). This would cause the star estimate to jump quite a bit. Most of the images in the pic are actual galaxies, with up to a 100 billion stars each, and not just single stars!

Hunter Arthur · Answer

undefined The number of stars in the universe is estimated by scientists using a variety of techniques, such as statistical models and telescope observations, by counting stars within a sample area and extrapolating based on the total observable universe.

Levi Anderson · Answer

undefined Scientists estimate the number of stars in the universe using various methods, including statistical extrapolation, observations, and theoretical models. One common approach involves observing a representative sample of galaxies and then extrapolating the average number of stars per galaxy to estimate the total number of galaxies in the observable universe. Multiplying this by the average number of stars per galaxy provides an estimate of the total number of stars.

Another method involves studying the luminosity function of stars within a galaxy. By measuring the brightness of stars and their distribution across different spectral types, scientists can infer the total number of stars based on the observed luminosity of the galaxy.

Additionally, theoretical models based on cosmological simulations and observations of the cosmic microwave background radiation provide constraints on the total mass and density of matter in the universe. By extrapolating these findings, scientists can estimate the number of stars that could have formed within the observable universe since its inception.

Overall, estimating the number of stars in the universe is a challenging task that relies on a combination of observational data, theoretical models, and statistical techniques. While uncertainties remain, current estimates suggest that there are roughly 100 billion to 200 billion galaxies in the observable universe, each containing millions to trillions of stars, resulting in a total estimate of around 1 trillion to 2 trillion stars.