An international team of astronomers led by University of Nottingham scientist Christopher Conselice has performed an accurate census of the number of galaxies in the observable Universe. They came to the conclusion that the Universe contains at least two trillion galaxies, nearly ten times as many as previously thought.
The image was taken by the NASA/ESA Hubble Space Telescope and covers a portion of the southern field of the Great Observatories Origins Deep Survey (GOODS). This is a large galaxy census, a deep-sky study by several observatories to trace the formation and evolution of galaxies. Image credit: NASA / ESA / Hubble.
Prof. Christopher and his colleagues from Leiden Observatory in the Netherlands and the Universities of Nottingham and Edinburgh in the UK reached this conclusion using images and other data from NASA’s Great Observatories (Spitzer, Hubble, and Chandra), ESA’s Herschel and XMM-Newton space telescopes.
The scientists painstakingly converted the images into 3D, in order to make accurate measurements of the number of galaxies at different times in the Universe’s history.
In addition, they used new mathematical models which allowed them to infer the existence of galaxies which the current generation of telescopes cannot observe.
This led to the surprising realization that in order for the numbers to add up, some 90% of the galaxies in the observable Universe are actually too faint and too far away to be seen — yet.
“This is very surprising as we know that, over the 13.7 billion years of cosmic evolution since the Big Bang, galaxies have been growing through star formation and mergers with other galaxies,” Prof. Christopher said.
“Finding more galaxies in the past implies that significant evolution must have occurred to reduce their number through extensive merging of systems.”
“We are missing the vast majority of galaxies because they are very faint and far away,” he said.
“The number of galaxies in the Universe is a fundamental question in astronomy, and it boggles the mind that over 90% of the galaxies in the cosmos have yet to be studied.”
“Who knows what interesting properties we will find when we study these galaxies with the next generation of telescopes?”
The team’s findings have been accepted for publication in the Astrophysical Journal (arXiv.org preprint).
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Christopher J. Conselice et al. 2016. The Evolution of Galaxy Number Density at z < 8 and its Implications. ApJ, accepted for publication; arXiv: 1607.03909
