The observable universe boasts at least 10 times as many galaxies as originally estimated, according to research published on Thursday in The Astrophysical Journal. This means that the cosmic census of galaxies, which has been conventionally pegged at around 100 to 200 billion, may be closer to a whopping two trillion individual galactic systems.
The surprising discovery is the result of a meticulous galactic survey mined from 15 years' worth of deep space observations from the Hubble Space Telescope. An international team led by University of Nottingham astrophysicist Christopher Conselice compiled the Hubble data into a three-dimensional timeline of galactic evolution over the universe's history.
This model reveals that only one in every 10 of the universe's galaxies are nearby enough or bright enough to be detected with the current slate of astronomical observatories. "It boggles the mind that over 90 percent of the galaxies in the universe have yet to be studied," Conselice said in a statement. "Who knows what interesting properties we will find when we observe these galaxies with the next generation of telescopes?"
Description of new research. Video: Hubble/ESA/YouTube
Many of these hidden systems are thought to be around the same scale of the many dwarf galaxies that orbit the Milky Way, rather than a large spiral structure like the Milky Way itself, which explains why they have escaped notice for so long.
But as Conselice hints, we may be on the brink of rooting out these dimmer galaxies with sophisticated new instruments like the James Webb Space Telescope, set for launch in 2018, or the European Extremely Large Telescope, which is scheduled to receive first light in 2024.
In the meantime, astronomers aim to continue reconstructing galactic evolution over the universe's 13.7-billion-year history. In their research, for instance, Conselice and his co-authors determined that the number of galaxies is dwindling over time as these massive star systems merge into ever-larger structures. Two trillion galaxies sounds like a colossal number now, but the galactic population in the universe's infancy was another tenfold higher, according to the team.
"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," Conselice said. "This gives us a verification of the so-called top-down formation of structure in the universe."
There's a great segment in the "The Backbone of Night" episode of Cosmos: A Personal Voyage in which Carl Sagan explains the grandeur of the universe to a classroom of schoolchildren.
"There are, in fact, 100 billion other galaxies, each of which contains something like a 100 billion stars," Sagan said. "Think of how many stars, and planets, and kinds of life there may be in this vast and awesome universe."
With astronomers now proposing that the cosmos is actually ten times more crowded than we imagined, this thought exercise has undoubtedly reached new levels of trippiness. It's a big universe out there, and we've barely scratched the surface.
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