Two Trillion Galaxies, at the Very Least
By HENRY FOUNTAIN OCT. 17, 2016
The scale of the universe, already unfathomable, just became even more so: There are about 10
times as many galaxies as previously thought.
The new number, two trillion galaxies, is the result of work led by Christopher J. Conselice, an
astrophysicist at the University of Nottingham in England, published last week in The
The team analyzed sky surveys by the Hubble Space Telescope and other instruments able to see
far away, and therefore far back, through about 13 billion years of time. The astronomers formed
three-dimensional models to measure the number of galaxies at different times.
Because not even the Hubble or large Earth-based telescopes can see the oldest, faintest galaxies,
they also did some mathematical work to come up with two trillion.
“It’s much bigger than anyone would have guessed,” Dr. Conselice said. “And the real number
could be even higher.”
Previous estimates were that there were perhaps 200 billion galaxies in the observable universe.
One might well ask — what difference does it make? Or put another way, once you get past a
couple of hundred billion galaxies, who’s counting?
But the finding has important implications for understanding how the universe has evolved.
The researchers found that most of the oldest galaxies were low in mass, similar to some of the
small “satellite” galaxies near our own Milky Way, and that there were about 10 times fewer
low-mass galaxies today. That suggests that over billions of years, galaxies have been colliding
and joining together.
The study also suggests how important the more powerful James Webb Space Telescope, set to
be launched in 2018, will be.
“It will be able to study these galaxies that we’re just barely detecting — these lower-mass
galaxies that are really the first galaxies of the universe,” Dr. Conselice said.