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.