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Video explaining light years and looking into the past.

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550-557

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Click on this link to open an article about the timeline and history of the Hubble Telescope

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The 1995 Hubble Photo that Changed Astronomy

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The 1995 Hubble Photo that Changed Astronomy

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This video Explains how the Hubble Deep Field image was created.

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The 1995 Hubble photo that changed astronomy

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This link will take you to a web page that has an article and a video explaining how we can determine how many galaxies are in the universe.

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The wonderful thing about science is that it's constantly searching for new evidence, revising estimates, throwing out theories, and sometimes discovering aspects of the Universe that we never realized existed.

The best science is skeptical of itself, always examining its own theories to find out where they could be wrong, and seriously considering new ideas to see if they better explain the observations and data.

What this means is that whenever I state some conclusion that science has reached, you can't come back a few years later and throw that answer in my face. Science changes, it's not my fault.

I get it, VY Canis Majoris isn't the biggest star any more, it's whatever the biggest star is right now. UY Scuti? That what it is today, but I'm sure it'll be a totally different star when you watch this in a few years.

What I'm saying is, the science changes, numbers update, and we don't need to get concerned when it happens. Change is a good thing. And so, it's with no big surprise that I need to update the estimate for the number of galaxies in the observable Universe. Until a couple of weeks ago, the established count for galaxies was about 200 billion galaxies.

But a new paper published in the Astrophysics Journal revised the estimate for the number of galaxies, by a factor of 10, from 200 billion to 2 trillion. 200 billion, I could wrap my head around, I say billion all the time. But 2 trillion? That's just an incomprehensible number.

Does that throw all the previous estimates for the number of stars up as well? Actually, it doesn't.

The observable Universe measures 13.8 billion light-years in all directions. What this means is that at the very edge of what we can see, is the light left that region 13.8 billion years ago. Furthermore, the expansion of the Universe has carried to those regions 46 billion light-years away.

Does that make sense? The light you're seeing is 13.8 billion light-years old, but now it's 46 billion light-years away. What this means is that the expansion of space has stretched out the light from all the photons trying to reach us.

What might have been visible or ultraviolet radiation in the past, has shifted into infrared, and even microwaves at the very edge of the observable Universe.

Since astronomers know the volume of the observable Universe, and they can calculate the density of the Universe, they know the mass of the entire Universe. 3.4 x 10^54 kilograms including regular matter and dark matter. They also know the ratio of regular matter to dark matter, so they can calculate the total amount of regular mass in the Universe.

In the past, astronomers divided that total mass by the number of galaxies they could see in the original Hubble data and determined there were about 200 billion galaxies.

Now, astronomers used a new technique to estimate the galaxies and it's pretty cool. Astronomers used the Hubble Space Telescope to peer into a seemingly empty part of the sky and identified all the galaxies in it. This is the Hubble Ultra Deep Field, and it's one of the most amazing pictures Hubble has ever captured.

Astronomers painstakingly converted this image of galaxies into a 3-dimensional map of galaxy size and locations. Then, they used their knowledge of galaxy structure closer to home to provide a more accurate estimate of what the galaxies must look like, out there, at the very edge of our observational ability.

For example, the Milky Way is surrounded by about 50 satellite dwarf galaxies, each of which has a fraction of the mass of the Milky Way.

By recognizing which were the larger main galaxies, they could calculate the distribution of smaller, dimmer dwarf galaxies that weren't visible in the Hubble images.

In other words, if the distant Universe is similar to the nearby Universe, and this is one of the principles of modern astronomy, then the distant galaxies have the same structure as nearby galaxies.

It doesn't mean that the Universe is bigger than we thought, or that there are more stars, it just means that the Universe contains more galaxies, which have less stars in them. There are the big main galaxies, and then a smooth distribution curve of smaller and smaller galaxies down to the tiny dwarf galaxies. The total number of stars comes out to be the same number.

The galaxies we can see are just the tip of the galactic iceberg. For every galaxy we can see, there are another 9, smaller fainter galaxies that we can't see.

Of course, we're just a few years away from being able to see these dimmer galaxies. When NASA's James Webb Space Telescope launches in October, 2018, it's going to be carrying a telescope mirror with 25 square meters of collecting surface, compared to Hubble's 4.5 square meters.

Furthermore, James Webb is an infrared telescope, a specialized tool for looking at cooler objects, and galaxies which are billions of light-years away. The kinds of galaxies that Hubble can only hint at, James Webb will be able to see directly.

So, why don't we see galaxies in all directions with our eyeballs? This is actually an old conundrum, proposed by Wilhelm Olbers in the 1700, appropriately named Olber's Paradox. We did a whole article on it, but the basic idea is that if you look in any direction, you'll eventually hit a star. It could be close, like the Sun, or very far away, but whatever the case, it should be stars in all directions. Which means that the entire night sky should be as bright as the surface of a star. Clearly it isn't, but why isn't it?

In fact, with 10 times the number of galaxies, you could restate the paradox and say that in every direction, you should be looking at a galaxy, but that's not what you see.

Except you are. Everywhere you look, in all directions, you're seeing galaxies. It's just that those galaxies are red-shifted from the visible spectrum into the infrared spectrum, so your eyeballs can't perceive them. But they're there.

When you see the sky in microwaves, it does indeed glow in all directions. That's the Cosmic Microwave Background Radiation, shining behind all those galaxies.

It turns out the Universe has 10 times more galaxies than previously estimated - 2 trillion galaxies. Not 10 times the stars or mass, those numbers have stayed the same.

And, once James Webb launches, those numbers will be fine-tuned again to be even more precise. 1.5 trillion? 3.4 trillion? Stay tuned for the better number.

Podcast (audio): Download (Duration: 7:20 - 2.7MB)

Subscribe: Apple Podcasts | Android | RSS

Podcast (video): Download (Duration: 7:22 - 95.2MB)

Subscribe: Apple Podcasts | Android | RSS

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How Many Galaxies Are There in the Universe? - Universe Today

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The wonderful thing about science is that it's constantly searching for new evidence, revising estimates, throwing out theories, and sometimes discovering aspects of the Universe that we never realized existed. The best science is skeptical of itself, always examining its own theories to find out where they could be wrong, and seriously considering new ideas to see if they better explain the observations and data.

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This resource also as a section that explains the answer to the fourth question.

# data[].attributes.attachment_link.readable_text
The wonderful thing about science is that it's constantly searching for new evidence, revising estimates, throwing out theories, and sometimes discovering aspects of the Universe that we never realized existed.

The best science is skeptical of itself, always examining its own theories to find out where they could be wrong, and seriously considering new ideas to see if they better explain the observations and data.

What this means is that whenever I state some conclusion that science has reached, you can't come back a few years later and throw that answer in my face. Science changes, it's not my fault.

I get it, VY Canis Majoris isn't the biggest star any more, it's whatever the biggest star is right now. UY Scuti? That what it is today, but I'm sure it'll be a totally different star when you watch this in a few years.

What I'm saying is, the science changes, numbers update, and we don't need to get concerned when it happens. Change is a good thing. And so, it's with no big surprise that I need to update the estimate for the number of galaxies in the observable Universe. Until a couple of weeks ago, the established count for galaxies was about 200 billion galaxies.

But a new paper published in the Astrophysics Journal revised the estimate for the number of galaxies, by a factor of 10, from 200 billion to 2 trillion. 200 billion, I could wrap my head around, I say billion all the time. But 2 trillion? That's just an incomprehensible number.

Does that throw all the previous estimates for the number of stars up as well? Actually, it doesn't.

The observable Universe measures 13.8 billion light-years in all directions. What this means is that at the very edge of what we can see, is the light left that region 13.8 billion years ago. Furthermore, the expansion of the Universe has carried to those regions 46 billion light-years away.

Does that make sense? The light you're seeing is 13.8 billion light-years old, but now it's 46 billion light-years away. What this means is that the expansion of space has stretched out the light from all the photons trying to reach us.

What might have been visible or ultraviolet radiation in the past, has shifted into infrared, and even microwaves at the very edge of the observable Universe.

Since astronomers know the volume of the observable Universe, and they can calculate the density of the Universe, they know the mass of the entire Universe. 3.4 x 10^54 kilograms including regular matter and dark matter. They also know the ratio of regular matter to dark matter, so they can calculate the total amount of regular mass in the Universe.

In the past, astronomers divided that total mass by the number of galaxies they could see in the original Hubble data and determined there were about 200 billion galaxies.

Now, astronomers used a new technique to estimate the galaxies and it's pretty cool. Astronomers used the Hubble Space Telescope to peer into a seemingly empty part of the sky and identified all the galaxies in it. This is the Hubble Ultra Deep Field, and it's one of the most amazing pictures Hubble has ever captured.

Astronomers painstakingly converted this image of galaxies into a 3-dimensional map of galaxy size and locations. Then, they used their knowledge of galaxy structure closer to home to provide a more accurate estimate of what the galaxies must look like, out there, at the very edge of our observational ability.

For example, the Milky Way is surrounded by about 50 satellite dwarf galaxies, each of which has a fraction of the mass of the Milky Way.

By recognizing which were the larger main galaxies, they could calculate the distribution of smaller, dimmer dwarf galaxies that weren't visible in the Hubble images.

In other words, if the distant Universe is similar to the nearby Universe, and this is one of the principles of modern astronomy, then the distant galaxies have the same structure as nearby galaxies.

It doesn't mean that the Universe is bigger than we thought, or that there are more stars, it just means that the Universe contains more galaxies, which have less stars in them. There are the big main galaxies, and then a smooth distribution curve of smaller and smaller galaxies down to the tiny dwarf galaxies. The total number of stars comes out to be the same number.

The galaxies we can see are just the tip of the galactic iceberg. For every galaxy we can see, there are another 9, smaller fainter galaxies that we can't see.

Of course, we're just a few years away from being able to see these dimmer galaxies. When NASA's James Webb Space Telescope launches in October, 2018, it's going to be carrying a telescope mirror with 25 square meters of collecting surface, compared to Hubble's 4.5 square meters.

Furthermore, James Webb is an infrared telescope, a specialized tool for looking at cooler objects, and galaxies which are billions of light-years away. The kinds of galaxies that Hubble can only hint at, James Webb will be able to see directly.

So, why don't we see galaxies in all directions with our eyeballs? This is actually an old conundrum, proposed by Wilhelm Olbers in the 1700, appropriately named Olber's Paradox. We did a whole article on it, but the basic idea is that if you look in any direction, you'll eventually hit a star. It could be close, like the Sun, or very far away, but whatever the case, it should be stars in all directions. Which means that the entire night sky should be as bright as the surface of a star. Clearly it isn't, but why isn't it?

In fact, with 10 times the number of galaxies, you could restate the paradox and say that in every direction, you should be looking at a galaxy, but that's not what you see.

Except you are. Everywhere you look, in all directions, you're seeing galaxies. It's just that those galaxies are red-shifted from the visible spectrum into the infrared spectrum, so your eyeballs can't perceive them. But they're there.

When you see the sky in microwaves, it does indeed glow in all directions. That's the Cosmic Microwave Background Radiation, shining behind all those galaxies.

It turns out the Universe has 10 times more galaxies than previously estimated - 2 trillion galaxies. Not 10 times the stars or mass, those numbers have stayed the same.

And, once James Webb launches, those numbers will be fine-tuned again to be even more precise. 1.5 trillion? 3.4 trillion? Stay tuned for the better number.

Podcast (audio): Download (Duration: 7:20 - 2.7MB)

Subscribe: Apple Podcasts | Android | RSS

Podcast (video): Download (Duration: 7:22 - 95.2MB)

Subscribe: Apple Podcasts | Android | RSS

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How Many Galaxies Are There in the Universe? - Universe Today

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The wonderful thing about science is that it's constantly searching for new evidence, revising estimates, throwing out theories, and sometimes discovering aspects of the Universe that we never realized existed. The best science is skeptical of itself, always examining its own theories to find out where they could be wrong, and seriously considering new ideas to see if they better explain the observations and data.

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This Is How We Know There Are Two Trillion Galaxies In The Universe

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This Is How We Know There Are Two Trillion Galaxies In The Universe

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Article with a link to a video that discusses how we arrived at the latest estimate of the number of galaxies.

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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.

Just how many galaxies are out there used to be 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 how faint 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 to 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 observatory to take data with. 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 get 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 that 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,

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 are more galaxies 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, two trillion 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 LSST, GMT, and the ELT, we're poised to reveal the hitherto unseen Universe as never before.

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This Is How We Know There Are Two Trillion Galaxies In The Universe

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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.

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Article that discusses the history and use of the Hubble telescope

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Galaxies are vast collections of stars that populate our universe. But how many galaxies are there? Counting them seems like an impossible task. Sheer numbers is one problem - once the count gets into the billions, it takes a while to do the addition. Another problem is the limitation of our instruments. To get the best view, a telescope needs to have a large aperture (the diameter of the main mirror or lens) and be located above the atmosphere to avoid distortion from Earth's air.

Perhaps the most resonant example of this fact is the Hubble eXtreme Deep Field (XDF), an image made by combining 10 years of photographs from the Hubble Space Telescope. The telescope watched a small patch of sky in repeat visits for a total of 50 days, according to NASA. If you held your thumb at arm's length to cover the moon, the XDF area would be about the size of the head of a pin. By collecting faint light over many hours of observation, the XDF revealed thousands of galaxies, both nearby and very distant, making it the deepest image of the universe ever taken at that time. So if that single small spot contains thousands, imagine how many more galaxies could be found in other spots.

While estimates among different experts vary, an acceptable range is between 100 billion and 200 billion galaxies, said Mario Livio, an astrophysicist at the Space Telescope Science Institute in Baltimore, Maryland. The James Webb Space Telescope is expected to reveal even more information about early galaxies in the universe, according to The Astrophysical Journal.

According to Livio, the Hubble Space Telescope has been successful for galaxy counting and estimation. The telescope, launched in 1990, initially had a distortion on its main mirror that was corrected during a shuttle visit in 1993. Hubble also went underwent several upgrades and service visits until the final shuttle mission there in May 2009.

In 1995, astronomers pointed the telescope at what appeared to be an empty region of Ursa Major, and collected 10 days' worth of observations. The result was an estimated 3,000 faint galaxies in a single frame, going as dim as 30th magnitude, according to Weber State University. (For comparison, the North Star or Polaris is at about 2nd magnitude.) This image composite was called the Hubble Deep Field and was the farthest anyone had seen into the universe at the time.

As the Hubble telescope received upgrades to its instruments, astronomers repeated the experiment twice. In 2003 and 2004, scientists created the Hubble Ultra Deep Field, which in a million-second exposure revealed about 10,000 galaxies in a small spot in the constellation Fornax.

In 2012, again using upgraded instruments, scientists used the telescope to look at a portion of the Ultra Deep Field. Even in this narrower field of view, astronomers were able to detect about 5,500 galaxies. Researchers dubbed this the eXtreme Deep Field.

All in all, Hubble reveals an estimated 100 billion galaxies in the universe or so, but this number is likely to increase to about 200 billion as telescope technology in space improves, Livio told Space.com.

Counting stars

Whatever instrument is used, the method of estimating the number of galaxies is the same. You take the portion of sky imaged by the telescope (in this case, Hubble). Then - using the ratio of the sliver of sky to the entire universe - you can determine the number of galaxies in the universe.

"This is assuming that there is no large cosmic variance, that the universe is homogenous," Livio said. "We have good reasons to suspect that is the case. That is the cosmological principle."

The principle dates back to Albert Einstein's theory of general relativity. Einstein said that gravity is a distortion of space and time. With that understanding in hand, several scientists (including Einstein) tried to understand how gravity affected the entire universe.

"The simplest assumption to make is that if you viewed the contents of the universe with sufficiently poor vision, it would appear roughly the same everywhere and in every direction," NASA stated. "That is, the matter in the universe is homogeneous and isotropic when averaged over very large scales. This is called the cosmological principle."

One example of the cosmological principle at work is the cosmic microwave background (CMB), radiation that is a remnant of the early stages of the universe after the Big Bang. Using instruments such as NASA's Wilkinson Microwave Anisotropy Probe, astronomers have found the CMB is virtually identical wherever one looks.

Would the number of galaxies change?

Measurements of the universe's expansion - through watching galaxies race away from us - show that it is about 13.82 billion years old. As the universe gets older and bigger, however, galaxies will recede farther and farther from Earth. This will make them more difficult to see in telescopes.

The universe is expanding faster than the speed of light (which does not violate Einstein's speed limit because the expansion is of the universe itself, rather than of objects traveling through the universe). Also, the universe is accelerating in its expansion.

This is where the concept of the " observable universe" - the universe that we can see - comes into play. In 1 trillion to 2 trillion years, Livio said, this means that there will be galaxies that are beyond what we can see from Earth.

"We can only see light from galaxies whose light had enough time to reach us," Livio said. "It doesn't mean that that's all there is in the universe. Hence, the definition of the observable universe."

Galaxies also change over time. The Milky Way is on a collision course with the nearby Andromeda Galaxy, and both will merge in about 4 billion years. Later on, other galaxies in our Local Group - the galaxies closest to us - will eventually combine. Residents of that future galaxy would have a much darker universe to observe, Livio said.

"Civilizations started then, they would have no evidence that there was a universe with 100 billion galaxies," he said. "They would not see the expansion. They would probably not be able to tell there was a Big Bang."

What about other universes?

As the early universe inflated, there are some theories that say that different "pockets" broke away and formed different universes. These different places could be expanding at different rates, include other types of matter, and have different physical laws than our own universe.

Livio pointed out there could be galaxies in these other universes - if they exist - but we have no way right now of knowing for sure. So the number of galaxies could even be greater than 200 billion, when considering other universes.

In our own cosmos, Livio said, astronomers will be better able to refine the number with the launch of the James Webb Space Telescope (for which his institute will manage the mission operations and science). Hubble is able to peer back at galaxies that formed about 450 million years after the Big Bang. Using the James Webb telescope, astronomers anticipate they can look as far back as 200 million years after the Big Bang.

"The numbers are not going to change much," Livio added, pointing out the first galaxies probably formed not too long before that. "So a number like 200 billion [galaxies] is probably it for our observable universe."

Webb's contributions

While it is interesting to count the number of galaxies in our universe, astronomers are more interested in how galaxies reveal how the universe was formed. According to NASA, galaxies are a representation of how matter in the universe was organized - at least, on the large scale. (Scientists are also interested in particle types and quantum mechanics, on the small side of the spectrum.) Because Webb can look back to the early days of the universe, its information will help scientists better understand the structures of the galaxies around us today.

"By studying some of the earliest galaxies and comparing them to today's galaxies, we may be able to understand their growth and evolution. Webb will also allow scientists to gather data on the types of stars that existed in these very early galaxies," NASA said of Webb's mission.

"Follow-up observations using spectroscopy of hundreds or thousands of galaxies will help researchers understand how elements heavier than hydrogen were formed and built up as galaxy formation proceeded through the ages. These studies will also reveal details about merging galaxies and shed light on the process of galaxy formation itself."

According to NASA, here are some of the key questions Webb will answer about galaxies:

How are galaxies formed?

What gives them their shapes?

How are the chemical elements distributed through the galaxies?

How do the central black holes in galaxies influence their host galaxies?

What happens when small and large galaxies collide or join together?

Scientists are also interested in the role that dark matter plays in the assembly of galaxies. While some of the universe is visible in forms such as galaxies or stars, dark matter is what makes up most of the universe - about 80 percent of it. While dark matter is invisible in wavelengths of light or through emissions of energy, studies of galaxies dating back to the 1950s indicated there was far more mass present in them than what was visible with the naked eye.

"Computer models that scientists have made to understand galaxy formation indicate that galaxies are created when dark matter merges and clumps together," NASA said.

"It [dark matter] can be thought of as the scaffolding of the universe. The visible matter we see collects inside this scaffolding in the form of stars and galaxies. The way dark matter 'clumps' together is that small objects form first, and are drawn together to form larger ones."

Webb's powerful mirrors will allow scientists to look at galaxy formation - including the role of dark matter - up close. While this investigation doesn't directly answer how many galaxies there are in the universe, it does help scientists better understand the processes behind the galaxies we see, which in turn better informs models about galactic populations.

Additional resources

You can see thousands of galaxies, taken in one photograph, in this image taken by NASA's Hubble Space Telescope. To read more about the different types of galaxies, head to NASA's Hubblesite.

Bibliography

"Oases in the dark: galaxies as probes of the Cosmos". Astrophysics and Astronomy Commons (2007). http://sciencejedi.com/professional/talks/ynp_galaxies.pdf

"Galaxy number counts - V. Ultradeep counts: the Herschel and Hubble Deep Fields". Monthly Notices of the Royal Astronomical Society, Volume 323, Issue 4 (2001). https://academic.oup.com/mnras/article/323/4/795/1102609?login=true

"Finding High-redshift Galaxies with JWST". The Astrophysical Journal (2021). https://iopscience.iop.org/article/10.3847/1538-4357/ac2a2f/meta

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How many galaxies are there? Astronomers have an estimate, but accurately counting them depends on several factors.

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Article published by NASA about the current count of galaxies in the universe.

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Hubble Finds 10 Times More Galaxies Than Thought

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The universe suddenly looks a lot more crowded than previously though thanks to a deep sky census by Hubble and major observatories.

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How can the Hubble Space Telescope look back in time?

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How can the Hubble Space Telescope look back in time?

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Article

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Video about the future James Webb telescope and how it will tell us more than Hubble.