Astrophysicists have revised their estimate of the number of galaxies in the universe upward tenfold by peering just 1 billion light-years deeper into the dark corners of the universe.
The new survey estimates that there are 2 trillion galaxies in the observable universe, up from the estimate of 120 billion made 20 years ago. Upgrades to the Hubble Space Telescope, along with data from other observatories, made the new estimate possible by letting astrophysicists look for galaxies 13 billion light-years away, some 1 billion light-year farther than before.
Here’s Davide Castelvecchi, reporting for Nature:
The team’s count was not too surprising, says astronomer Steven Finkelstein at the University of Texas at Austin, but it’s still helpful to put a number on it. “I don’t know of anyone who has done this before,” he says. [Lead author Christopher] Conselice says that theorists had expected the number to be even higher; he and his collaborators now plan to look into this discrepancy.
There are a number of ways the discrepancy might have crept in. To arrive at their figure, Conselice and his team counted the number of galaxies they could observe using Hubble and the other telescopes and then filled in the blanks using highly educated guesses about the galaxies that are too faint to see. The previous survey in the 1990s faced a similar problem, but the older figure was also skewed because astronomers at the time figured the universe looked the same in all directions, though they had only studied a slice of it known as the Hubble Deep Field image.
The actual number extant today is likely smaller than 2 trillion since many of the galaxies seen by astrophysicists have merged since their light first started its journey to Earth.
Expect the estimate to be revised again in a few years—the James Webb Space Telescope will give us a deeper view of the cosmos after it is launched in 2018.