We already estimated that there were about 100 billion galaxies in the observable universe, but new research shows that this estimate is at least 10 times too low!
First, what is the observable universe? Well, it is the most distant part of the universe we can see from Earth because, in theory, the light from these objects have had time to reach Earth.
In a new study using surveys taken by the Hubble Space Telescope and other observatories, astronomers came to the surprising conclusion that there are at least 10 times more galaxies in the observable universe than previously thought. This places the universe’s estimated population at, minimally, 2 trillion galaxies!
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?
Most of these newly discovered galaxies were relatively small and faint, with masses similar to those of the satellite galaxies surrounding the Milky Way.
Using deep-space images from the Hubble Space Telescope and other observatories, astronomers converted the images into 3-D, in order to make accurate measurements of the number of galaxies at different epochs in the universe’s history.
In addition, they used new mathematical models, which allowed them to infer the existence of galaxies that the current generation of telescopes cannot observe. This led to the surprising conclusion that in order for the numbers of galaxies we now see and their masses to add up, there must be a further 90% of galaxies in the observable universe that are too faint and too far away to be seen with present-day telescopes.
The myriad small faint galaxies from the early universe merged over time into the larger galaxies we can now observe.
That means that over 90% of the galaxies in the universe have yet to be studied! In the near future, the James Webb Space Telescope will be able to study these ultra-faint galaxies and give us more information about their existence.
So back to the question…Why is the sky dark at night if the universe contains an infinity of stars? Researchers 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.
