Although we know the universe is extremely vast and contains a myriad galaxies, a new study posits that we have underestimated the number of those galaxies by a whopping 90 percent. Instead of there being between 100 and 200 billion, there are 2 trillion, and the enormous disparity in the total comes from those galaxies we currently cannot observe.
Phys.org reported this week that an international team of astronomers have determined, after 15 years of galaxy-counting and extrapolating from the data derived from the observable universe, that the universe, by extension, contains t2 trillion galaxies. Christopher Conselice, Professor of Astrophysics at the University of Nottingham, and his team of researchers used pencil beam deep space images obtained by telescopes around the world, including from the NASA Hubble Space Telescope, into 3-D maps. The maps were then used to calculate the density and volume of galaxies in each region of space, thus allowing the researchers to compare between regions. This provided the foundation for the estimate of galaxies that have not been observed.
Estimates of the number of galaxies over the years have depended on images of the observable universe or that part of the cosmos where light reaches the Earth. In the past two decades, astronomers have relied on images taken by the Hubble Space Telescope to obtain a galaxy census.
The most recent, as Medium reported in 2014, estimated that there were between 100 and 200 billion galaxies in the observable universe. This was determined by analyzing 13 images taken over a decade by the Hubble telescope (after it was outfitted with the Advanced Camera for Surveys in 2002) and combining them into one image and labeled the Extreme Deep Field (XDF). In what we know is only a small portion of the sky, the XDF encompassed 5,500 galaxies. Astronomers derived the observable universe galaxy count by multiplying the XDF region of space by the number of like-sized regions it would take to fill the Earth’s sky.
Conselice’s team, along with scientists from the Leiden Observatory at Leiden University in the Netherlands and the Institute for Astronomy at the University of Edinburgh, derived the results of the latest study from counting the number of galaxies in a given epoch (period to time) and determining that there were quite a bit more galaxies in earlier time periods.
The study found that when the universe was young, only a few billion years old, a given volume of space held 10 times the number of galaxies than exists in that same volume of space at present.
Professor Conselice said, “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. Finding more galaxies in the past implies that significant evolution must have occurred to reduce their number through extensive merging of systems.”
He went on, “We are missing the vast majority of galaxies because they are very faint and far away. 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 observable universe stands to get even larger — and the number count of galaxies even more accurate — as technology advances and more sensitive telescopes are deployed. For instance, NASA’s James Webb Space Telescope, which is slated for launch in October 2018, has a mirror nearly three times the size of Hubble and is equipped with four instruments capable of detecting and recording extremely faint signals.
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