Cosmic census of galaxies updated to 2 trillion

Previous galactic count multiplied by factor of 10

Hubble image

GALAXY BONANZA  The observable universe might be home to roughly 2 trillion galaxies, a new study suggests. In this image from the Hubble Space Telescope, nearly every spot of light is a galaxy.  

NASA, ESA, the GOODS Team, and M. Giavalisco/University of Massachusetts Amherst

Two trillion galaxies. That’s the latest estimate for the number of galaxies that live — or have lived — in the observable universe, researchers report online October 10 at This updated headcount is roughly 10 times greater than previous estimates and suggests that there are a lot more galaxies out there for future telescopes to explore.

Hordes of relatively tiny galaxies, weighing as little as 1 million suns, are responsible for most of this tweak to the cosmic census. Astronomers haven’t directly seen these galaxies yet. Christopher Conselice, an astrophysicist at the University of Nottingham in England, and colleagues combined data from many ground- and space-based telescopes to look at how the number of galaxies in a typical volume of the universe has changed over much of cosmic history. They then calculated how many galaxies have come and gone in the universe.

The galactic population has dwindled over time, as most of those 2 trillion galaxies collided and merged to build larger galaxies such as the Milky Way, the researchers suggest. That’s in line with prevailing ideas about how massive galaxies have been assembled. Seeing many of these remote runts, however, is beyond the ability of even the next generation of telescopes. “We will have to wait at least several decades before even the majority of galaxies have basic imaging,” the researchers write.

Christopher Crockett is an Associate News Editor. He was formerly the astronomy writer from 2014 to 2017, and he has a Ph.D. in astronomy from the University of California, Los Angeles.

More Stories from Science News on Astronomy