“Space is big. Really big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist, but that’s just peanuts to space.” – The Hitchhiker’s Guide to the Galaxy
The Universe is indeed big, so massive in scale that our brains can hardly grasp or understand it. And now new findings from the Hubble Space Telescope show that it is even more so than first thought. Previous surveys indicated that the universe contained around 200 billion or so galaxies, which is staggering as it is. But newly updated research now shows the number is actually about 10 times that, or 2 trillion galaxies.
In the mid-1990s, the Hubble Deep Field images provided the first good glimpse into how many galaxies populated the observable universe, and the consensus at the time was about 100-200 billion. With an estimated few hundred billion stars in most galaxies, like ours, it provided a perspective on just how inconsequential our little planet, and even our Solar System, seemed to be.
But now a new research team, led by Christopher Conselice from the University of Nottingham in the UK, has shown that this estimate is at least 10 times too low. Their results will be published soon in the Astrophysical Journal. The new paper is currently available here. Just like in the previous surveys, the team used Hubble images for their work. In order to make an accurate assessment of the number of galaxies at different times in the Universe’s history, they converted the images into 3-D versions. New mathematical models also helped the team to infer the existence of galaxies which cannot be observed by the current generation of telescopes.
The result was a surprise: 90 percent of the galaxies in the observable Universe are still too faint and distant to be seen.
“It boggles the mind that over 90% of the galaxies in the Universe have yet to be studied. Who knows what interesting properties we will find when we observe these galaxies with the next generation of telescopes,” said Conselice.
It’s a well-known aspect of astronomy that the more distant an object is, the further back in time we are seeing it, since it takes that much longer for the light from it to reach us. The team observed galaxies dating more than 13 billion years in the past. This revealed some other interesting results. Galaxies have not been evenly distributed through the Universe’s history. When the Universe was younger, only a few billion years old, there were about 10 times more galaxies per unit volume, but they were smaller than most of the galaxies we see today. The evidence shows that galaxies have tended to clump together over time, creating larger galaxies but fewer of them. The mass of the Universe didn’t change, it was just distributed among smaller, more numerous galaxies than it is now.
“This gives us a verification of the so-called top-down formation of structure in the Universe,” said Conselice. “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,” he added.
As he also noted for the Royal Astronomical Society: “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.”
The findings also help to explain another puzzle, known as Olbers’ paradox: If there are still so many galaxies, why is the sky dark at night? The answer seems to simply be that most galaxies are still too distant and faint to be seen by the human eye, or even telescopes.
We’ve all seen the numerous Hubble photos of space filled with many, many galaxies. It is almost inconceivable to think that we are still only seeing about 10 percent of all the galaxies out there.
As reported on AmericaSpace last year, Hubble had also observed the largest group of faintest and youngest galaxies ever seen. Those galaxies, over 250 of them, are estimated to have formed only 600 million years after the Big Bang.
According to lead author Hatim Atek: “If we took into account only the contributions from bright and massive galaxies, we found that these were insufficient to reionize the Universe. We also needed to add in the contribution of a more abundant population of faint dwarf galaxies.”
In that research, gravitational lensing was used to obtain the images of three galaxy clusters.
“Hubble remains unrivaled in its ability to observe the most distant galaxies. The sheer depth of the Hubble Frontier Field data guarantees a very precise understanding of the cluster magnification effect, allowing us to make discoveries like these,” said study co-author Mathilde Jauzac, from Durham University in the U.K., and the University of KwaZulu-Natal in South Africa.
It should also be noted that, as explained by Phil Plait on Slate, the increased number of galaxies doesn’t mean there are also 10 times as many stars or that the Universe is 10 times larger; the stars are simply distributed among many more galaxies than known before.
It is expected that the James Webb Space Telescope, scheduled to launch in 2018, will be able to view more of these yet-unseen galaxies.
“In the near future, the James Webb Space Telescope will be able to study these ultra-faint galaxies,” Conselice noted in Wired.
Some other interesting facts about Hubble:
- Hubble has made more than 1.2 million observations since its mission began in 1990.
- Astronomers using Hubble data have published more than 12,800 scientific papers, making it one of the most productive scientific instruments ever built.
- Hubble does not travel to stars, planets, or galaxies. It takes pictures of them as it whirls around Earth at about 17,000 mph.
- Hubble has traveled more than 3 billion miles along a circular low Earth orbit currently about 340 miles in altitude.
- Hubble has no thrusters. To change pointing angles, it uses Newton’s third law by spinning its wheels in the opposite direction. It turns at about the speed of a minute hand on a clock, taking 15 minutes to turn 90 degrees.
Hubble has the pointing accuracy of .007 arc seconds, which is like being able to shine a laser beam on a dime 200 miles away.
- Outside the haze of our atmosphere, Hubble can see astronomical objects with an angular size of 0.05 arc seconds, which is like seeing a pair of fireflies in Tokyo from your home in Maryland.
- Hubble has peered back into the very distant past, to locations more than 13.4 billion light years from Earth.
- The Hubble archive contains more than 100 Terabytes, and Hubble science data processing generates about 10 Terabytes of new archive data per year.
- Hubble weighed about 24,000 pounds at launch and currently weighs about 27,000 pounds following the final servicing mission in 2009 (on the order of two full-grown African elephants).
- Hubble’s primary mirror is 2.4 meters (7 feet, 10.5 inches) across.
- Hubble is 13.3 meters (43.5 feet) long (the length of a large school bus).
Hubble was also recently in the news for its new observations of possible water vapor plumes on Jupiter’s ocean moon Europa, showing how it continues to make exciting discoveries both inside and outside of our Solar System.
The late astronomer Carl Sagan is famous for his “billions and billions” quotes. Now it seems even that may be an understatement as we learn just how staggeringly immense the Universe really is.
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