Uh-oh, You're Going to Need a Bigger Telescope

Astronomers from the University of Nottingham conducted a new survey of the universe’s galaxy population and concluded that previous estimates lowballed the census by a factor of about 20. Using data from Hubble and telescopes around the world, as well as a new mathematical model, they estimate that there are ten times more galaxies in the observable universe than we thought; previous estimates put the number of galaxies in the universe at around 200 billion.

To understand how the researchers accomplished their task, we first need to understand what they mean by the “observable universe.” Because the speed of light is fixed, we can never get a true picture of what the universe looks like right now. As we look farther and farther away, we must necessarily look further back in time as well.

So, in discovering how many galaxies exist in the observable universe, the Nottingham researchers haven’t discovered how many galaxies exist right now, they’ve found out how many galaxies we would be able to see if our instruments were good enough. This may seem like a big caveat, but it’s the only way can observe the far-flung universe. Being able to look back in time has its advantages, however.

To reach their conclusion, the researchers looked at the rate of galaxy mergers throughout the universe. Most galaxies likely started small, and grew through a series of mergers with other galaxies as time went on. Because the researchers could see clusters further and further back in time as they looked deeper, they could compare the concentration of galaxies long ago to more recent times — relatively speaking.

They found that galaxies appear to clump together as time goes by, forming larger structures while also reducing the total number of galaxies present. By running this rate backward, and extrapolating beyond what we can currently see, the researchers concluded that around 90 percent of the galaxies out there are too faint and too far away to view with current telescopes. This is what allowed them to drastically increase our estimation of the number of observable galaxies.