Back in the 1990's, Hubble Deep Field images gave astronomers an unprecedented look into the depths of the universe. What they saw there was nothing short of awe-inspiring: galaxies, billions of them. Every dot of light in their images represented a galaxy, each teeming with stars and, presumably, planets too. By the time everything could be accounted for, estimates put the number of galaxies in the known universe to somewhere between 100 and 200 billion, and that's been the working model ever since.
But a thorough new analysis, made possible with more advanced modern modeling technology, suggests those previous estimates may have been too low — way too low. The numbers of galaxies in the observable universe may need to be counted in trillions, not billions.
The international team of astronomers, led by Christopher Conselice from the University of Nottingham, U.K., found that older estimates were likely 10 times too low, according to a press release. The team reached their conclusion after painstakingly converting all known Deep Field images into 3-D. This also enabled them to make accurate measurements of the number of galaxies at different times in the universe’s history. New mathematical models were also applied, which allowed the team to estimate the number of galaxies that are likely to exist beyond the view of our best telescopes today.
“It boggles the mind that over 90 percent of the galaxies in the Universe have yet to be studied. Who knows what interesting properties we will find when we observe these galaxies with the next generation of telescopes,” said Conselice.
Part of the reason for the large discrepancy between early estimates and the new figures is that we now know galaxies are not evenly distributed throughout the universe’s history. They come in clusters. Earlier models did not take this into account, so the distribution of galaxies appeared to be spread a lot thinner across the cosmos than they actually are. Also, not all galaxies are created equal. Some are larger, brighter. Just because some galaxies are too faint to appear on our images doesn't mean they aren't there.
Furthermore, as the universe has aged, many galaxies have also merged, which is another factor leading to low estimates.
The new findings also offer insight into the so-called Olbers’ paradox, the mystery as to why the night sky is dark despite the fact that it is so widely populated by objects of light. Because the universe has been so dynamic throughout its history — because galaxies are not evenly distributed throughout the cosmos — the dark skies we witness with the human eye when we look up at night can be chalked up this distribution and dynamism.
So, perhaps anti-intuitively, it makes sense that the sky is dark even though there may be 10 times more galaxies out there than ever imagined before.