This story appeared in the June 2020 issue as "A Universe of Galaxies."Subscribeto Discover magazine for more stories like this.
On the evening of Oct. 4, 1923, near Los Angeles, a young astronomer got into his car and began a motorized trek up to Mount Wilson. There, he arrived at the observatory that housed the 100-inch Hooker Telescope, at the time the largest telescope in the world.
Edwin Hubble was a fourth-year astronomer at Mount Wilson; he enjoyed using the Hooker Telescope because he was interested in, among other things, studying spiral “nebulae.” These mysterious gas clouds were scattered across the sky, and no one understood their nature. In the early days of the 1920s, Hubble had assigned himself the task of figuring them out.
He pointed the great telescope toward his favorite object: the nebula in Andromeda, M31. This spiral-shaped cloud is faintly visible to the naked eye under a clear, moonless sky. He then captured its image on a photographic plate. Hubble was excited by the result. On it, he found a suspected nova, an exploding star. The next night, he photographed M31 again, hoping to catch the nova and record it under better atmospheric stability. The second plate did indeed record the nova, but little did he know, he also had captured a plate that would become legendary in the history of science.
Astronomer Edwin Hubble made an exposure of the “Andromeda Nebula” with the Hooker Telescope at Mount Wilson Observatory near Los Angeles on Oct. 5, 1923. He was initially excited, believing he had recorded a nova, an exploding star. He marked the star, which lies between two tick marks he drew at the top right on the plate, with the letter N. The star turned out to be a Cepheid variable, and Hubble used it to prove that the distance to the Andromeda Galaxy was far greater than astronomers thought. (Credit: Courtesy of the Carnegie Observatories/Cindy Hunt)
His observing time over, he returned to his office to analyze the catch. Suddenly, Hubble made an astonishing realization: The nova was not a nova at all, but a particular type of star that changed its brightness, a Cepheid variable. Checking earlier plates, he was able to confirm that, and he realized that the star’s faintness had incredible implications.
The star, and the nebula that encompassed it, must lie at a distance of a million light-years — three times larger than anyone at the time believed the size of the whole universe to be. Today, thanks to improved measurements, astronomers know the object is 2.5 million light-years away.
Aided in part by earlier work done by Vesto M. Slipher and by his own colleague, Milton Humason, Hubble had at once discovered that the universe was far larger than anyone had believed, and that spiral nebulae like Andromeda were actually distant galaxies. They were whole systems of stars and gas, separated from our own Milky Way by a long hike.
At Arizona’s Lowell Observatory, as early as 1912, Slipher had recorded the apparent velocities of spiral nebulae and, with the work now done by Hubble, it was clear the universe was expanding — the galaxies were flying apart from one another over time. The universe was not only far larger than anyone had previously believed, but it was growing as time went on.
NGC 4565 in Coma Berenices is the brightest and most prominent galaxy in our sky that is oriented perfectly edge-on to our line of sight. We see its disk as a thin, silvery needle. Some 57 million light-years off, it lies in the Virgo Cluster and has a prominent central bulge, suggesting it may be a barred spiral. (Credit: Adam Block)
By 1929, astronomers had put a cosmic picture of the past together. If you traced the histories of many of the galaxies backward in time, it meant that the cosmos began with a small, infinitely dense point at its origin. This research was an extension of work originally done by Belgian astronomer Georges Lemaître. Astronomers understood this cosmic point of origin, later called the Big Bang, as the start of the universe, and, they calculated, it must have occurred billions of years ago. The Big Bang had commenced the expansion that was driving all the galaxies away from each other as time rolls on. The whole universe seemed to be flying apart.
In the 1930s, Hubble began to study and classify galaxies into their various so-called morphological types, the array of structures astronomers saw in photographs. He eventually assembled the types of galaxies he observed into a tuning fork-shaped diagram. It contained spiral galaxies, barred spiral galaxies — spirals containing a linear “bar” of material passing through their centers — lenticular (lens-shaped) galaxies, and elliptical galaxies. He also identified irregular galaxies, clouds of stars and gas that lacked an organized shape. Later on, astronomers would identify peculiar galaxies, systems that appeared to be wracked with explosive or disruptive events. They also identified a class of galaxies called dwarf spheroidals, which seemed to be numerous in the local universe.
By the 1950s, French astronomer Gérard de Vaucouleurs of the University of Texas had expanded Hubble’s classification scheme into a more complex system that took into account many observed properties of galaxies. De Vaucouleurs produced a pseudo-three-dimensional plot showing the galaxies’ relationships, nicknamed the “Cosmic Lemon” due to its shape. De Vaucouleurs included details on bars in galaxies, descriptions of rings of matter visible in them, and an evaluation of how loosely or tightly the spiral arms of a galaxy were wound. He also included evaluative details about the nature of irregular and peculiar galaxies.
The last generation of extragalactic astronomy has moved into far more sophisticated analyses than cataloging. By using the Hubble Space Telescope, astronomers have estimated that some 100 billion galaxies must exist in the cosmos. And the number may be much greater than that. Probably some 2 trillion galaxies existed in the early universe, but it seems clear that galaxies near each other are drawn together by gravity and combine over cosmic time. Despite the universal expansion, then, normal galaxies like the Milky Way are probably made of dozens or more protogalaxies that merged into larger systems. You can see these primitive blobs of matter, bluish protogalaxies, in the early universe within the Hubble Ultra Deep Field pictures.
Our Own Galaxy
Perseus A, also called NGC 1275, is an eruptive galaxy at the core of the Perseus Cluster, which is made up of some 1,000 galaxies about 240 million light-years away. The dominant member of the Perseus Cluster, Perseus A is a Seyfert galaxy with an active nucleus, powered by a 340-million-solar-mass black hole in its core. (Credit: Hubble Legacy Archive, ESA, and NASA)
As astronomers have studied greater numbers of galaxies over the past few decades, they’ve discovered many things, but one that is impossible to ignore is that the universe is incredibly large. If you look at a galaxy in your telescope’s eyepiece tonight, the photons striking your eye have been traveling at the fastest speed there is — 186,000 miles per second (300,000 kilometers per second). Nonetheless, they have taken 2.5 million years at that velocity to reach us from the Andromeda Galaxy. And that object is nearly on our cosmic doorstep. Of course, the knowledge of our own galaxy, in a primitive sense, goes back to antiquity. The name Milky Way comes from the Latin via lactea, which derives from the original idea, the Greek term, galaxías kýklos, “milky circle.” The band of Milky Way visible in our sky, most prominently in the summer and winter evenings, is the unresolved light from billions of stars lying along the plane of our galaxy.
But only in the past few decades have we come to understand that the Milky Way is one of the 100 billion galaxies in the universe, and that its disk stretches some 100,000 light-years across. It contains some 400 billion stars, although we don’t know exactly how many because dwarf stars are faint and difficult to see over long distances. For decades, astronomers believed the Milky Way was a simple spiral galaxy. But studies in this century have shown the Milky Way is a barred spiral, and that our sun and solar system lie some 26,000 light-years from the center, in one of the galaxy’s arms.
The Milky Way consists of a bright disk, a slowly spinning platter of stars and gas that contains most of the stars we see. Our sun orbits the center of the galaxy once every 220 million years, meaning that we’ve rotated around the galactic center about 20 times since the formation of the solar system. Far away, in the center of the galaxy, lies a supermassive black hole containing around 4.3 million times more mass than the sun. In recent times, astronomers have discovered that supermassive black holes in the centers of galaxies are the norm. Nearly all galaxies, except for dwarfs, have them.
The galaxy’s disk is encapsulated by a halo of a small number of stars, along with huge spheres of ancient stars called globular star clusters, and a big envelope of dark matter. Astronomers don’t yet know what dark matter consists of, but they know it is there because of the gravitational influence it has on the visible matter they can observe.
The Local Group
The weirdly distorted elliptical galaxy NGC 474 in Pisces lies at a distance of 100 million light-years. The neighboring spiral galaxy NGC 470 lies just above it. Multiple shells and tidal tails surround NGC 474, caused by interactions with its neighbors and by density waves that propagate through the medium. This mammoth object stretches 250,000 light-years across — two and a half times the diameter of the Milky Way. (Credit: P-A. DUC (CEA, CFHT), ATLAS 3D Collaboration)
The Milky Way is hardly alone in the cosmos. It belongs to a group of at least 54 objects called the Local Group of galaxies, a name Hubble gave to this local cloud of objects as he mapped the nearby cosmos. The primary members of the Local Group are the Milky Way, the Andromeda Galaxy, and the Pinwheel Galaxy (M33). But each of these big three spirals has a cloud of attendant galaxies, too. The Milky Way’s satellites include the Large and Small Magellanic Clouds, visible to the naked eye in the Southern Hemisphere, and many dwarf galaxies. The diameter of the Local Group is about 10 million light-years, some 100 times the diameter of the Milky Way.
And moving outward into the deeper universe, we encounter more examples of those 100 billion galaxies. These majestic islands of stars and gas exist in groups, like our Local Group, but also in larger assemblages called clusters and very large ones called superclusters. Despite the overall expansion of the universe, meaning that most galaxies are moving away from each other as the cosmos grows, gravity keeps smaller numbers of galaxies bound to each other on their journeys. Our Local Group, for example, is a member of the so-called Virgo Cluster of galaxies, named so because its richly populated center lies in the constellation Virgo in our sky.
The Virgo Cluster contains at least 1,500 galaxies and is centered some 54 million light-years from Earth. You can see some of the brightest galaxies near the core of the Virgo Cluster in amateur telescopes, in an array called Markarian’s Chain. This line of galaxies contains supermassive elliptical galaxies such as M84 and M86, and a variety of spiral galaxies, too. For backyard astronomers, this playground of galaxy types is one of the really entrancing areas of the sky, and it is best visible on springtime evenings under clear, moonless conditions.
Most of the Virgo Cluster galaxies contain supermassive black holes in their centers. M87 is quite an example. Whereas the Milky Way’s central black hole weighs in at 4.3 million solar masses, the colossal black hole inside M87 contains an estimated mass of 5 billion to 7 billion suns, some 1,000 times more massive than ours. M87 is one of the largest galaxies in our part of the universe — it is a so-called cD galaxy, short for centrally dominant — and it has “eaten” many of the smaller galaxies that once surrounded it. That’s what massive galaxies do — they consume their neighborhood partners.
One of the greatest edge-on galaxies in the sky, and the one most people say looks like a flying saucer, is the Sombrero Galaxy (M104) in Virgo. It consists of a great rotating disk with a prominent dust lane edging it, consumed by a glowing halo of gas and stars. It lies 43 million light-years away and is about half the size of the Milky Way, sporting a diameter of 49,000 light-years. (Credit: NASA and the Hubble Heritage Team (AURA/STScI))
A cluster containing 1,500 galaxies is one thing, but much larger assemblages of galaxies also exist. The Virgo Cluster itself is a member of the so-called Virgo Supercluster, which holds thousands of galaxies on a scale an order of magnitude larger yet. The Virgo Supercluster holds our Milky Way, the Local Group, the Virgo Cluster, and altogether some 100 galaxy groups and clusters. This amazingly large framework stretches some 110 million light-years across, and is one of about 10 million superclusters that make up the entire cosmos.
Despite the huge number of galaxies existing in the Virgo Supercluster, astronomers now know that most of the space in this volume is essentially empty. The diameters of these great voids range from dozens to hundreds of millions of light-years. Filamentary chains of galaxies wind their way around the dark, empty spaces. On large scales, galaxies in clusters and superclusters are like soap bubbles, with galaxies coating the surfaces and voids lying in between.
The Whirlpool Galaxy in Canes Venatici, another galaxy near the Big Dipper, is also known as M51 and is a top telescope target. An interacting pair of galaxies, the Whirlpool is being passed by a little interloper, NGC 5195, which is drawing material off one of the larger galaxy’s spiral arms. The pair lies 23 million light-years away, and M51’s disk stretches across 60,000 light-years. (Credit: Tony Hallas)
By the end of the 1980s, astronomers had identified the Great Wall, a sheet of galaxies measuring 500 million light-years across. More recently, the Sloan Digital Sky Survey uncovered the Sloan Great Wall, an assemblage of galaxies at least twice the size of the Great Wall, which covers a long dimension of some 1.4 billion light-years.
As astronomers discovered more and more distant galaxies, they found that some large mass seemed to be tugging on the local universe, pulling us in the direction of the southern constellations Triangulum Australe and Norma. Called the Great Attractor, this anomaly, some 200 million light-years away, puzzled astronomers. They eventually discovered that an even larger mass in that direction was pulling us. This mammoth structure, called the Shapley Supercluster, is 650 million light-years away and contains the greatest concentration of galaxies in our local part of the cosmos.
The Big Picture
Elliptical galaxies like M49 in Virgo are huge spheres of stars that float in an ellipsoidal cloud. Althoughtheir diameters are often similar to large spiral galaxies, they can hold vastly more mass because they are shaped like a football rather than a disk. This galaxy lies some 56 million light-years away and is one of the more massive galaxies in the Virgo Cluster. (Credit: NASA/ESA/STScI)
Additional surprising discoveries have occurred, too. In 2014, astronomers identified a new supercluster based on the relative motions of galaxies analyzed in a more sophisticated way than ever before. University of Hawai‘i astronomers concluded that the Laniakea Supercluster exists, and named it after the Hawaiian word for “immense heaven.”
Laniakea, which is also sometimes called the Local Supercluster, contains some 100,000 galaxies, including the Local Group and the Milky Way. This massive cluster and all its members are traveling together through space, but not all of the galaxies within it are gravitationally bound. Some will splinter apart from the rest of the cluster as time rolls on.
The Laniakea Supercluster has four major components — the Virgo Supercluster, the Hydra-Centaurus Supercluster, the Pavo-Indus Supercluster, and the Southern Supercluster.
Altogether, Laniakea contains around 500 galaxy clusters and groups. And surrounding Laniakea in the local universe are other galaxy superclusters — the Shapley Supercluster, the Hercules Supercluster, the Coma Supercluster, and the Perseus-Pisces Supercluster. Each of these structures holds hundreds of galaxy clusters and are linked by the fabriclike web of cosmic structure.
Beginning in the 1980s, astronomers found evidence of structures even larger than superclusters. At first, objects now called Large Quasar Groups (LQG) baffled astronomers.
In 1982, Scottish astronomer Adrian Webster found what would become known as the Webster Large Quasar Group, a collection of five quasars, or actively feeding black holes, stretching over 330 million light-years. Now, nearly two dozen LQGs are known. A structure known as the Huge LQG contains 73 quasars over a diameter of some 4 billion light-years. This massive structure, dismissed by some astronomers, may hold the title as the largest collection of related matter in the cosmos.
Truly, the universe is so big that it’s hard to comprehend. On one hand, the enormity of the universe makes us feel small. Our brief lives happen so quickly, and we wink out, mostly unaware of the incredibly large cosmos around us. But the fact that we are sentient, that we can ponder the stars and galaxies far away from us, makes life in the universe a truly amazing thing. And we’re just starting to get to know the immense world of galaxies.
David J. Eicher is the editor of Astronomy. His 2020 book, Galaxies: Inside the Universe’s Star Cities, is available from My Science Shop.
One such estimate says that there are between 100 and 200 billion galaxies in the observable universe. Other astronomers have tried to estimate the number of 'missed' galaxies in previous studies and come up with a total number of 2 trillion galaxies in the universe.How many galaxies are there and how did astronomers figure this out? ›
This tiny patch of sky was full of galaxies, almost 10,000, of all different sizes and shapes. By multiplying this number by the number of times this tiny patch of sky would fit into the entire sky, astronomers came up with an estimate of between about 100 and 200 billion galaxies.How many galaxies are distributed by astronomers? ›
"So a number like 200 billion [galaxies] is probably it for our observable universe."How many named galaxies are there? ›
There are about 51 galaxies in the Local Group (see list of nearest galaxies for a complete list), on the order of 100,000 in the Local Supercluster, and an estimated 100 billion in all of the observable universe.How many galaxies do astronomers estimate are in the universe according to data from NASA's New Horizons space probe? ›
Subsequent sensitive observations such as Hubble's Ultra Deep Field revealed a myriad of faint galaxies. This led to an estimate that the observable universe contained about 200 billion galaxies.How many galaxies do we estimate there are in the universe? ›
One such estimate says that there are between 100 and 200 billion galaxies in the observable universe. Other astronomers have tried to estimate the number of 'missed' galaxies in previous studies and come up with a total number of 2 trillion galaxies in the universe.How many galaxies do you think there are in the universe? ›
If we made the most straightforward estimate using today's best technology, we'd state there are 170 billion galaxies in our Universe.How much of the universe have we discovered? ›
Scientists estimate that the radius of the universe could be as large as 46.5 billion years, so the distance into space humans can currently observe would represent a little less than one-third of the total distance.How many galaxies and solar systems are there in the universe? ›
With ~2 trillion galaxies within our observable Universe, we can extrapolate our Universe's planetary total.How many known universes are there? ›
There is only one Universe we currently know of, and that is the Universe in which we already live.
- Spiral Galaxies. This stunning view of spiral galaxy M101, also known as the Pinwheel galaxy, was captured by the Hubble Space Telescope. ...
- Elliptical Galaxies. ...
- Lenticular Galaxies. ...
- Irregular Galaxies. ...
- Seyfert Galaxies. ...
The Milky Way Galaxy. Our Sun (a star) and all the planets around it are part of a galaxy known as the Milky Way Galaxy. A galaxy is a large group of stars, gas, and dust bound together by gravity. They come in a variety of shapes and sizes.What are the 3 main galaxies names? ›
There are three general types: elliptical, spiral, and irregular.How many galaxies are estimated to be visible in the Hubble ultra deep field? ›
Called the Hubble Ultra Deep Field (HUDF), the image contains as many as 10,000 galaxies of all shapes, sizes, colors, and ages.How many galaxies are there in the observable universe astronomy quizlet? ›
50 billion to 100 billion galaxies in the observable universe (5 x 1010 to 1011) ... each with 1 billion to 100 billion stars per galaxy (109 to 1011) So, in total, as many as 1011 x 1011 = 1022 stars in the observable universe —and most stars probably have planets!How many galaxies are there in the part of the universe we can observe quizlet? ›
How many galaxies are in our observable universe? Approximately 100 billion galaxies!How many galaxies are in universe 7? ›
There are only four galaxies in Universe 7. Within these galaxies are planets. Planet Earth is in the North Galaxy aka the Milky Way.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.Is there more than one universe? ›
Our universe is but one in an unimaginably massive ocean of universes called … the multiverse. If that concept isn't enough to get your head around, physics describes different kinds of multiverse. The easiest one to comprehend is called the cosmological multiverse.Are there infinite galaxies? ›
Our universe is just a finite number of galaxies rushing away from each other inside this empty infinite space—like a solitary skyrocket exploding and sending out a doomed shower of sparks." But many cosmologists say, no, there are an infinite number of galaxies in our infinite space.
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.How many more years will the Earth last? ›
Earth will interact tidally with the Sun's outer atmosphere, which would decrease Earth's orbital radius. Drag from the chromosphere of the Sun would reduce Earth's orbit. These effects will counterbalance the impact of mass loss by the Sun, and the Sun will likely engulf Earth in about 7.59 billion years.How many trillions of years will universe last? ›
Roughly 1 trillion years from now, the last star will be born. In about 100 trillion years, the last light will go out. The bad news is that the universe is going to die a slow, aching, miserable death. The good news is that we won't be around to see it.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.How many black holes are there in the universe? ›
40,000,000,000,000,000,000. With a new computational approach, SISSA researchers have been able to make the fascinating calculation. Moreover, according to their work, around 1% of the overall ordinary (baryonic) matter is locked up in stellar mass black holes.Will we ever travel to another galaxy? ›
At present, travelling to another galaxy is not possible. However, advances in technology and further research and development may someday make interstellar travel a reality. Even then, travelling between galaxies is not an easy task; the distances are immense, so travel would take an extremely long time.How do astronomers find galaxies? ›
For more-distant galaxies, astronomers rely on the exploding stars known as supernovae. Like Cepheids, the rate at which a certain class of supernovae brighten and fade reveals their true brightness, which then can be used to calculate their distance.Who proved there were many galaxies? ›
Astronomer Edwin Hubble announces that the spiral nebula Andromeda is actually a galaxy and that the Milky Way is just one of many galaxies in the universe.How many galaxies and stars do scientists think there are? ›
Using the Milky Way as our model, we can multiply the number of stars in a typical galaxy (100 billion) by the number of galaxies in the universe (2 trillion).How many galaxies are there in the James Webb Telescope? ›
The seven galaxies confirmed by Webb were first established as candidates for observation using data from the Hubble Space Telescope's Frontier Fields program. The program dedicated Hubble time to observations using gravitational lensing, to observe very distant galaxies in detail.
Among its famous observations is the Hubble Ultra Deep field, the deepest image of the universe ever made at visible and near-infrared wavelengths, and revealed over 10,000 galaxies in a small patch of sky.
Mostly we see stars in the Milky Way galaxy. But, with telescopes, we can even see other galaxies!Who created the universe? ›
According to the Book of Genesis, God created the universe - and all the heavenly bodies, the sun, the moon, and the stars - in six days. But according to contemporary cosmologists the universe began with a great explosion known as the Big Bang, after which the stars and galaxies slowly formed over billions of years.Who is the first galaxy in the universe? ›
Up until the discovery of JADES-GS-z13-0 in 2022 by the James Webb Space Telescope, GN-z11 was the oldest and most distant known galaxy yet identified in the observable universe, having a spectroscopic redshift of z = 10.957, which corresponds to a proper distance of approximately 32 billion light-years (9.8 billion ...Who named the universe? ›
John Herschel developed and popularized a system of naming celestial objects that embraced classical models, avoiding attempts at nationalism and aggrandizement.How many galaxies can be viewed from Earth? ›
The Andromeda Galaxy is the only other (besides the Milky Way) spiral galaxy we can see with the naked eye.How many universes are in the multiverse? ›
The American theoretical physicist and string theorist Brian Greene discussed nine types of multiverses: Quilted. The quilted multiverse works only in an infinite universe. With an infinite amount of space, every possible event will occur an infinite number of times.