When you gaze up at the night sky, through the veil of stars and the plane of the Milky Way close by, you can’t help but feel small before the grand abyss of the Universe that lies beyond. Even though nearly all of them are invisible to our eyes, our observable Universe, extending tens of billions of light years in all directions, contains a fantastically large number of galaxies within it.
The exact number of galaxies out there has been a mystery, with estimates rising from the thousands to the millions to the billions, all as telescope technology improved. If we made the most straightforward estimate using today’s best technology, we’d state there are 170 billion galaxies in our Universe. But we know more than that, and our modern estimate is even grander: two trillion galaxies. Here’s how we got there.
In an ideal world, we’d simply count them all. We’d point our telescopes at the sky, cover the entire thing, collect every photon emitted our way, and detect every object that was out there, no matter how faint. With arbitrarily good technology and an infinite amount of resources, we’d simply measure everything in the Universe, and that would teach us how many galaxies are out there.
But in practice, that won’t work. Our telescopes are limited in size, which in turn limits how many photons they can collect and the resolutions they can achieve. There’s a trade-off between the faintness of an object you can see and how much of the sky you can take in at once. Some of the Universe is obscured by intervening matter. And the more distant an object is, the fainter it appears; at some point, a source is far enough away that even observing for a century won’t reveal such a galaxy.
So what we can do, instead, is to view a clear portion of the Universe without intervening matter, stars, or galaxies as deeply as possible. The longer you stare at a single patch of sky, the more light you’ll collect and the more you’ll reveal about it. We first did this in the mid-1990s with the Hubble Space Telescope, pointing at a patch of sky that was known to have practically nothing in it, and simply sit on that spot and let the Universe reveal what was present.
It was one of the riskiest strategies of all-time. If it failed, it would have been a waste of over a week of observing time on the newly-corrected Hubble Space Telescope, the most sought-after data collection observatory. But if it succeeded, it promised to reveal a glimpse of the Universe in a way we had never seen before.
We collected data for hundreds of orbits, across a multitude of different wavelengths, hoping to reveal galaxies that were fainter, more distant, and harder to see than any we had detected before. We hoped to learn what the ultra-distant Universe really looked like. And when that first image finally was processed and released, we got a view unlike any other.
Everywhere we looked, in all directions, there were galaxies. Not just a few, but thousands upon thousands of them. The Universe wasn’t empty and it wasn’t dark; it was full of light-emitting sources. As far as we were capable of seeing, stars and galaxies were clumped and clustered everywhere.
But there were other limits. The most distant galaxies are caught up in the expansion of the Universe, causing distant galaxies to redshift past the point where our optical and near-infrared telescopes (like Hubble) could detect them. Finite sizes and observing times meant that only the galaxies above a certain brightness threshold could be seen. And very small, low-mass galaxies, like Segue 3 in our own backyard, would be far too faint and small to resolve.
So we could push past our technological limits from that mid-1990s image, but even so, we could never record all the galaxies. The best attempt we ever made was the Hubble eXtreme Deep Field (XDF), which represented a composite image of ultraviolet, optical, and infrared data. By observing just a tiny patch of sky so small it would take 32 million of them to cover all the possible directions we could look, we accumulated a total of 23 days worth of data.
Stacking everything together into a single image revealed something never-before seen: a total of approximately 5,500 galaxies. This represented the highest density of galaxies ever observed through a narrow, pencil-like beam in space.
You might think, therefore, that we could estimate the number of galaxies in the Universe by taking the number we observed in this image and multiplying it by the number of such images it would take to cover the entire sky.
In fact, you can get a spectacular number by doing so: 5500 multiplied by 32 million comes out to an incredible 176 billion galaxies.
But that’s not an estimate; that’s a lower limit. Nowhere in that estimate do the too-faint, too-small, or too-close-to-another galaxies show up. Nowhere do the galaxies obscured by the neutral gas and dust appear, nor do the galaxies located beyond the redshift capabilities of Hubble. Yet, just as those galaxies exist nearby, they ought to exist in the young, distant Universe as well.
The big ingredient we need to come up with a true estimate, then, is how structure accurately forms in the Universe. If we can run a simulation that starts with:
- the ingredients that make up the Universe,
- the right initial conditions that reflect our reality,
- and the correct laws of physics that describe nature,
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we can simulate how such a Universe evolves. We can simulate when stars form, when gravity pulls matter into large enough collections to create galaxies, and to compare what our simulations predict with the Universe, both near-and-far, that we actually observe.
Perhaps surprisingly, there were more galaxies in the early Universe than there are today. But unsurprisingly, they’re smaller, less massive, and are destined to merge together into the old spirals and ellipticals that dominate the Universe we inhabit at present. The simulations that match best with reality contain dark matter, dark energy, and small, seed fluctuations that will grow, over time, into stars, galaxies, and clusters of galaxies.
Most remarkably, when we look at the simulations that match the observed data the best, we can extract, based on our most advanced understanding, which clumps of structure should equate to a galaxy within our Universe.
When we do exactly that, we get a number that’s not a lower-limit, but rather an estimate for the true number of galaxies contained within our observable Universe. The remarkable answer?
As of today,twotrillion galaxies should exist within our observable Universe.
Yet, that number is so remarkably different from the lower-limit estimate we came up with from the Hubble eXtreme Deep Field image. Two trillion versus 176 billion means that more than 90% of the galaxies within our Universe are beyond the detection capabilities of even humanity’s greatest observatory, even if we look for nearly a month at a time.
Over time, galaxies merged together and grew, but small, faint galaxies still remain today. Even in our own Local Group, we’re still discovering galaxies that contain mere thousands of stars, and the number of galaxies we know of have increased to more than 70. The faintest, smallest, most distant galaxies of all are continuing to go undiscovered, but we know they must be there. For the first time, we can scientifically estimate how many galaxies are out there in the Universe.
The next step in the great cosmic puzzle is to find and characterize as many of them as possible, and understand how the Universe grew up. Led by the James Webb Space Telescope and the next generation of ground-based observatories, including the Vera Rubin Observatory, the Giant Magellan Telescope, and the European Extremely Large Telescope, we’re poised to reveal the hitherto unseen Universe as never before.
Ethan is on vacation. Please enjoy this older article from the Starts With A Bang archives!
It is estimated that there are roughly 200 billion galaxies (2×1011) in the observable universe. Most galaxies are 1,000 to 100,000 parsecs in diameter (approximately 3,000 to 300,000 light years) and are separated by distances on the order of millions of parsecs (or megaparsecs).How many galaxies are there in Milky Way? ›
There are around fifty galaxies in the Milky Way, the largest of which is the Large Magellanic Cloud. This satellite galaxy has a diameter of only 14,000 light-years. The Large Magellanic Cloud may have as many as 10 billion stars within it.How many solar systems are in a galaxy? ›
The Short Answer: Our planetary system is the only one officially called “solar system,” but astronomers have discovered more than 3,200 other stars with planets orbiting them in our galaxy. Our solar system is just one specific planetary system—a star with planets orbiting around it.Which is the biggest galaxy? ›
A spectacular new photo has been released showing the record-holder for largest galaxy in the universe. NGC 6872, also known as the Condor Galaxy, stretches 522,000 light years from tip to tip. The Milky Way is approximately 100,000 light years across.How many universes are in space? ›
We currently have no evidence that multiverses exists, and everything we can see suggests there is just one universe — our own.How many galaxies will collide with the Milky Way? ›
Andromeda–Milky Way collision
Our Milky Way galaxy is destined to collide with our closest large neighbour, the Andromeda galaxy, in about five billion years. Scientists can predict what's going to happen.
But the Andromeda galaxy is a whole separate galaxy, even bigger than our Milky Way. In a dark sky, you can see that it's big on the sky as well, a smudge of distant light larger than a full moon. View at EarthSky Community Photos. | Randy Shetter in California, captured this photo of Andromeda on August 7, 2021.What is beyond the universe? ›
The trite answer is that both space and time were created at the big bang about 14 billion years ago, so there is nothing beyond the universe. However, much of the universe exists beyond the observable universe, which is maybe about 90 billion light years across.What is our universe called? ›
Therefore, our universe is called the cosmos.What universe are we in? ›
The Sun is one among hundreds of billions of stars in the Milky Way galaxy, and most of those stars have their own planets, known as exoplanets. The Milky Way is but one of billions of galaxies in the observable universe — all of them, including our own, are thought to have supermassive black holes at their centers.
The biggest single entity that scientists have identified in the universe is a supercluster of galaxies called the Hercules-Corona Borealis Great Wall. It's so wide that light takes about 10 billion years to move across the entire structure.Is there a star bigger than our galaxy? ›
The largest known star in the universe is UY Scuti. It has an estimated radius of 1.188 billion kilometers. If UY Scuti were the center of our solar system, its photosphere, or outer shell, would reach just past the orbit of Jupiter.How big is the oldest galaxy? ›
|Mass||~1×109 M ☉|
|Size||4,000 ± 2,000 ly (1,200 ± 610 pc)|
|Apparent size (V)||0.6arcsec|
The world as we know it has three dimensions of space—length, width and depth—and one dimension of time. But there's the mind-bending possibility that many more dimensions exist out there. According to string theory, one of the leading physics model of the last half century, the universe operates with 10 dimensions.Who is the creator of this universe? ›
Many religious persons, including many scientists, hold that God created the universe and the various processes driving physical and biological evolution and that these processes then resulted in the creation of galaxies, our solar system, and life on Earth.How many worlds exist? ›
More than 5,000 worlds exist beyond our solar system. There could be billions more | CNN.Will humans ever leave the Milky Way? ›
The technology required to travel between galaxies is far beyond humanity's present capabilities, and currently only the subject of speculation, hypothesis, and science fiction. However, theoretically speaking, there is nothing to conclusively indicate that intergalactic travel is impossible.Is there life on Andromeda galaxy? ›
Can the Andromeda Galaxy support life? Since we can't yet say for certain whether there are any other stars in our own galaxy that host life, it is even harder to say whether there might be life, or at least the conditions for life, in another galaxy.Will Earth be destroyed when Milky Way collides? ›
Our Milky Way galaxy will likely collide with the neighboring Andromeda galaxy four billion years from now. Our Sun will fling into a new region of our galaxy, but our Earth and solar system are in no danger of being destroyed.What is the closest galaxy to Earth? ›
The closest known galaxy to us is the Canis Major Dwarf Galaxy, at 236,000,000,000,000,000 km (25,000 light years) from the Sun. The Sagittarius Dwarf Elliptical Galaxy is the next closest , at 662,000,000,000,000,000 km (70,000 light years) from the Sun.
Proxima Centauri, the closest star to our own, is still 40,208,000,000,000 km away. (Or about 268,770 AU.)
The nearby Andromeda Galaxy, also called M31, is bright enough to be seen by the naked eye on dark, moonless nights. The Andromeda Galaxy is the only other (besides the Milky Way) spiral galaxy we can see with the naked eye.Are there 12 galaxies? ›
It is estimated that there are roughly 200 billion galaxies (2×1011) in the observable universe. Most galaxies are 1,000 to 100,000 parsecs in diameter (approximately 3,000 to 300,000 light years) and are separated by distances on the order of millions of parsecs (or megaparsecs).What is a galaxy vs universe? ›
A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity. The Universe consists of billions of galaxies. For example, The Milky Way Galaxy is just one galaxy in the Universe.How many galaxies can we see from Earth? ›
The Andromeda Galaxy is the only other (besides the Milky Way) spiral galaxy we can see with the naked eye.Which is the biggest planet in the Milky Way? ›
Fifth in line from the Sun, Jupiter is, by far, the largest planet in the solar system – more than twice as massive as all the other planets combined.
Generally, they conclude, life is possible only in the outer regions of large galaxies. (Our own solar system is about 27,000 light-years from the center.)Which galaxy is Earth in? ›
We live on a planet called Earth that is part of our solar system. But where is our solar system? It's a small part of the Milky Way Galaxy.What comes after the universe? ›
The trite answer is that both space and time were created at the big bang about 14 billion years ago, so there is nothing beyond the universe. However, much of the universe exists beyond the observable universe, which is maybe about 90 billion light years across.What is bigger than universe? ›
As it stands, the universe is the largest object that we are aware of. There is nothing larger, and everything we can smell, hear, taste, touch, or see is a part of it.
Because space isn't curved they will never meet or drift away from each other. A flat universe could be infinite: imagine a 2D piece of paper that stretches out forever.Is there a life In The Andromeda Galaxy? ›
Can the Andromeda Galaxy support life? Since we can't yet say for certain whether there are any other stars in our own galaxy that host life, it is even harder to say whether there might be life, or at least the conditions for life, in another galaxy.Is Andromeda moving towards us? ›
The Andromeda Galaxy (M31) is indeed approaching us, by about 300 kilometers (190 miles) per second measured with respect to the Sun. If you subtract the Sun's orbital motion around our galaxy (about 230 km per second toward Cygnus), M31 is still approaching the Milky Way by about 130 km per second.Which planet is the coldest? ›
Uranus holds the record for the coldest temperature ever measured in the Solar System: a very chilly -224℃. The temperature on Neptune is still very cold, of course – usually around -214℃ – but Uranus beats that. The reason why Uranus is so cold is nothing to do with its distance from the Sun.