Published: Fri, October 14, 2016
Research | By Jennifer Evans

Galaxy count may now top 2 trillion across universe

Galaxy count may now top 2 trillion across universe

Scientists' initial estimate was that there are about 100 billion galaxies.

This also helps to solve a problem known as "Olbers" paradox, ' which asks why the sky is dark at night.

In one pocket of the early universe, when the cosmos was just a few billion years old, researchers found ten times the number of galaxies found in a similar portion of the galaxy today.

The team looked more than 13 billion years into the past and found that galaxies are not evenly distributed throughout the universe's history. "This gives us a verification of the so-called top-down formation of structure in the universe", said Professor Christopher Conselice, the study's lead author. The images were converted into 3D, allowing the researchers to make accurate measurements of the number of galaxies at various stages in the universe's history.

Modern explanations suggest the universe is finite, has an age, and is expanding faster and faster, which (according to a discovery by Edwin Hubble in 1929) shifts the light of the most distant stars to colors that human eyes can't see.

Thought the universe was crowded with 100 billion to 200 billion galaxies?

Over the last 15 years, researcher Christopher Conselice has been working with an worldwide team of astronomers to translate telescope images into a 3D map of the visible universe. By running this rate backward, and extrapolating beyond what we can now see, the researchers concluded that around 90 percent of the galaxies out there are too faint and too far away to view with current telescopes. Because the researchers could see clusters further and further back in time as they looked deeper, they could compare the concentration of galaxies long ago to more recent times - relatively speaking. That scenario holds that there were many more galaxies in the young universe but that the number is lower now because many galaxies merged.

Ninety percent of galaxies in the observable universe are too dim and distant to be seen today, according to the new research; ten percent can be seen. "Who knows what interesting properties we will find when we observe these galaxies with the next generation of telescopes", explains Christopher Conselice about the far-reaching implications of the new results.

He added that NASA's James Webb Space Telescope, which is set to launch in 2018, will be able to study these ultra-faint galaxies.

The decreasing number of galaxies as time progresses also contributes to the solution for Olbers' paradox (first formulated in the early 1800s by German astronomer Heinrich Wilhelm Olbers): Why is the sky dark at night if the universe contains an infinity of stars? The team came to the conclusion that there is such an abundance of galaxies that, in principle, every point in the sky contains part of a galaxy. But the light from these stars is invisible to us ― in part because of the continuing expansion of the universe and because the light is absorbed by intergalactic dust and gas.

A very dark section of the night sky photographed by Great Observatories Origins Deep Survey.

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