2 Trillion Galaxies

As if we didn’t feel small and insignificant already, The Guardian reports,

There are a dizzying 2 trillion galaxies in the universe, up to 20 times more than previously thought, astronomers reported on Thursday. The surprising finding, based on 3D modeling of images collected over 20 years by the Hubble Space Telescope, was published in the Astronomical Journal.

Scientists have puzzled over how many galaxies the cosmos harbors at least since US astronomer Edwin Hubble showed in 1924 that Andromeda, a neighboring galaxy, was not part of our own Milky Way. But even in the era of modern astronomy, getting an accurate tally has proven difficult.

To begin with, there is only part of the cosmos where light given off by distant objects has had time to reach Earth. The rest is effectively beyond our reach. And even within this “observable universe”, current technology only allows us to glimpse 10% of what is out there, according to the new findings.

“Using deep space images from Hubble,” the article continues, “Conselice and his team painstakingly converted them into 3D to measure the number of galaxies at different times in the history of the universe. The analysis reached back more than 13bn years – very near the time of the “Big Bang” thought to have given birth to the universe.” These findings have some astounding implications:

The results have clear implications for galaxy formation, and also helps shed light on an ancient astronomical paradox — why is the sky dark at night?

In analyzing the data, a team led by Christopher Conselice of the University of Nottingham, U.K., found that 10 times as many galaxies were packed into a given volume of space in the early universe than found today. Most of these galaxies were relatively small and faint, with masses similar to those of the satellite galaxies surrounding the Milky Way. As they merged to form larger galaxies the population density of galaxies in space dwindled. This means that galaxies are not evenly distributed throughout the universe’s history, the research team reports in a paper to be published in The Astrophysical Journal.

“These results are powerful evidence that a significant galaxy evolution has taken place throughout the universe’s history, which dramatically reduced the number of galaxies through mergers between them — thus reducing their total number. This gives us a verification of the so-called top-down formation of structure in the universe,” explained Conselice.

So why is the sky so dark at night if it is populated with galaxies?:

The team came to the conclusion that indeed there actually is such an abundance of galaxies that, in principle, every patch in the sky contains part of a galaxy. However, starlight from the galaxies is invisible to the human eye and most modern telescopes due to other known factors that reduce visible and ultraviolet light in the universe. Those factors are the reddening of light due to the expansion of space, the universe’s dynamic nature, and the absorption of light by intergalactic dust and gas. All combined, this keeps the night sky dark to our vision.

The universe just gets bigger and stranger.