The universe — or at least the “observable universe,” the part we're theoretically capable of detecting from Earth — is much more crowded than scientists had thought. Previous estimates, based on the Hubble Deep Field images captured in the mid-1990s, suggested that around 100 billion or 200 billion galaxies swirled within our line of detection. But a new analysis suggests a figure 10 times higher than that: There may be 2 trillion galaxies in the observable universe, 90 percent of which are too faint for our best telescopes to detect.
Led by Christopher Conselice from the University of Nottingham, astronomers used all available data to construct a 3-D map of the universe around us, which allowed them to chart the number of galaxies that existed at different periods in history — the farther away a telescope looks, the further back in time it looks, because we're seeing light that has had to travel longer distances to reach the lens. The team's mathematical models indicate that for the universe to behave as it does, there must be more than a trillion galaxies unaccounted for. Their results are set to be published soon in the Astrophysical Journal.
By looking 13 billion years into the past, Conselice's team also found that there was not an even distribution of galaxies throughout the universe's history. When the universe was young — just millions and billions of years old compared with 13.8 billion years it now has under its belt — it contained 10 times as many galaxies per unit volume. While the mass of the universe didn't change, it was distributed across a greater number of spunky, small galaxies than the layout we see closer to home.
“This gives us a verification of the so-called top-down formation of structure in the universe,” Conselice said in a statement — the idea that the universe started small, creating lots of tiny galaxies that would grow and merge into the behemoths we observe today.
“We are missing the vast majority of galaxies because they are very faint and far away,” he added in another statement. “The number of galaxies in the universe is a fundamental question in astronomy, and it boggles the mind that over 90 percent of the galaxies in the cosmos have yet to be studied. Who knows what interesting properties we will find when we study these galaxies with the next generation of telescopes?”
Conselice estimated to the LA Times that the James Webb Space Telescope, set to launch in 2018, will “more than double” the number of galaxies that humans can observe. But if Conselice's latest findings are correct, that still leaves more than a trillion galaxies well beyond our reach.