Space
History of the world; From the Big Bang to the creation of the planet Earth
History of the world; From the Big Bang to the creation of the planet Earth
Since its launch in 2021, the James Webb Space Telescope has sent us spectacular images of the universe’s deep field. This telescope revealed fine details like a galaxy with an age of 13.1 billion. Such distant objects may not be visually impressive, appearing as fuzzy red blobs in images, but they can provide a fascinating glimpse into the universe’s infancy.
Space and time are intertwined. Light travels at a constant speed, so the images captured by telescopes like James Webb’s are actually images of the universe from millions or even billions of years ago. The higher the sensitivity and accuracy of a telescope, the more distant objects it can observe and thus display more distant times. As the most powerful telescope ever launched, the James Webb Space Telescope (JWST) is extremely sensitive. This telescope can theoretically see objects within 100 million years since the formation of the universe.
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The first moments
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Initial plasma
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The world becomes transparent
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Cosmic Dark Age
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The first habitable age
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The first lights in the dark
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Blooming cosmos with stars
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Star seeds
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The oldest known star
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The oldest known planet
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The formation of galaxies
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Large-scale structures of the universe
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Collision of galaxies
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Massive black holes
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The formation of the Milky Way disc
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Overcoming dark energy
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The birth of the sun
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The formation of the earth
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The first forms of life
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Extraterrestrial life and alien civilizations
There are still many unknowns about the history of the universe, but telescopes like Webb’s can unravel these mysteries and reveal unprecedented detail.
History of the world
The first moments
The universe was born about 13.8 billion years ago from the Big Bang.
The entire universe was created from an ancient and vast explosion that continues to this day. This spark , called the Big Bang, happened nearly 13.8 billion years ago. The Big Bang is the best hypothesis ever proposed for the existence of the universe. Although there is still no way to directly observe the Big Bang, this theory is well established and has been confirmed by many scientists over the past few decades.
In the first moments of the universe, a fraction of a second after the Big Bang, everything was inside a singularity, which is an infinitesimally small point of space with a very strange and high density that encompasses everything. In a few moments after the birth of the universe, the world was in an era known as Planck’s age. In this era, the whole world was so small that space and time had no meaning. Then, in less than a second, the universe entered a phase known as cosmic inflation, and for a moment, it expanded greatly. The infant universe consisted of a hot soup of subatomic particles and radiation, preventing any kind of structure from forming.
Initial plasma
The universe was initially filled with turbid, hot plasma.
The early universe was a highly viscous place filled with turbid plasma for several thousand years. This murky plasma was a mass of subatomic particles that were too hot to contract into atoms. The lack of transparency of the early world makes it impossible to see the events of that time; However, the early chapters of the universe’s history are of interest to many cosmologists because they represent a stage for the existence of everything.
Scientists believe that the early universe was filled with equal amounts of matter and antimatter, which eventually annihilated each other, leaving only a small amount of matter in the present universe. The question of why one of them was more remains a mystery and physicists are still trying to answer this question.
Eventually, the universe cooled and atoms and then strange molecules began to form. The first molecule that was formed in the world was made of only two elements, hydrogen and helium. These molecules finally made a compound called helium hydride. This chemical reaction actually created a helium compound that looks like it shouldn’t exist.
The world becomes transparent
The world became transparent after 300 thousand years.
On its 300,000 birthday, the world entered an era known as the age of recombination. It was during this period that atoms began to form, although the word “recombination” is a bit of a misnomer because it was during this period that everything was combined together for the first time. As the universe cooled enough, matter began to form atoms, and the universe became transparent for the first time. This transparency allowed the light left over from the Big Bang to spread throughout the universe.
The ancient Big Bang radiation marks the edge of the visible universe and can still be observed. As the universe continues to expand, the light in it is stretched, which astronomers witness in the form of the redshift phenomenon. The older the light of an object, the more it is stretched and moves to the red side of the spectrum like infrared and finally to longer wavelengths.
The initial light of the birth of the world is the most stretched light and the human eye cannot observe it. This light can be seen in all directions today as the cosmic background radiation (CMB). As seen in the image above, some speckled areas show slight fluctuations left over from cosmic inflation. These faint background rays are the last reflections of the birth of the universe.
Cosmic Dark Age
The world had no stars in the dark ages.
With the universe filled with atoms, light was finally able to move freely in open space. However, there was nothing in the universe capable of producing light. In fact, this age of the world is known as the age of cosmic darkness. In this period, the stars were not yet born and the space was full of silence and infinite darkness. The universe was in its infancy and there was nothing but dark matter with neutral helium and hydrogen, But it was in this darkness that the materials of the world gradually joined each other.
Finally, with the formation of the first stars, the world entered an era known as the Bazion, and the first stars shone. They emitted intense ultraviolet light in the dark and eventually removed the electrons from the new atoms; But even though the stars were shining for the first time in the universe, their light could not travel very far. Because the entire space was filled with a fog of hydrogen gas and blocked the light of the first stars. After some time, the starlight traveled further distances and reached us today.
The first habitable age
According to calculations, the first habitable age started in 10-17 million years of the world.
According to human earth standards, any place with liquid water can be classified as habitable. As the early Earth cooled, the surprising truth was revealed that the entire universe was once at a habitable temperature. According to an article published in the International Journal of Astrophysics, this period is called the early habitable age. Based on this hypothesis, the question arises as to what exactly happened in a world where life theoretically existed everywhere. According to calculations, this cosmic age corresponds to the time when the universe was still 10 to 17 million years old.
Of course, scientists have differences in this hypothesis. According to an article in Nature that argues against this idea, life requires a hot-to-cold energy flow and cannot exist in a uniformly warm universe. Furthermore, at this early age it is not known whether the universe had stars or planets, or even oxygen to produce water. However, this hypothesis cannot be completely rejected. The first planets were probably formed in the first few billion years of the universe; So the hypothesis of an early habitable age is little more than a fascinating thought experiment.
History of the world
The first lights in the dark
The first stars of the universe were composed of light elements.
The first stars of the universe were formed from the virgin material left over from the Big Bang and were the cause of the formation of the first heavy elements of the universe. These stars, which lacked elements heavier than helium, are known as population 3 stars (confusingly named stellar populations in the wrong order). Since these stars were responsible for the formation of the heavy elements of the universe, they must have existed at some point in history. These objects are expected to have formed between 100 million and 250 million years after the Big Bang.
According to the models, Population 3 stars were very massive and short-lived by today’s stellar standards. The lifetime of some of these stars reached only 2 million years, which is a long time from the human point of view; But on a stellar scale, it’s like a blink of an eye. When these stars ended their lives, they likely perished in unstable binary supernova explosions, the most violent type of stellar explosion in the universe. Although no stars belonging to this group have been observed so far, perhaps this trend will change with powerful instruments such as the James Webb Space Telescope.
Blooming cosmos with stars
Some stars of the Milky Way date back to 11 to 13 billion years ago.
We live in a season of the world known as the age of star formation. This age is the beginning of the stars shining in the dark and is actually the modern age of the world, in which the cosmic matter turns into stars, planets and galaxies. According to scientists, the era of star formation began approximately one million years after the Big Bang and will continue until the universe is 100 trillion years old. Until the very distant future, the birth, life and death of stars in the universe and the fusion of hydrogen into heavier elements will continue until hydrogen disappears completely.
Although stars are actively forming in the universe, there is a wide range from newly born stars to very old stars. Stars can live for billions of years. Red dwarfs, the smallest and most populous stars in the universe, live so long that their deaths have not been recorded until now because the universe is not old enough. Astronomers have also observed very old stars in the universe, some of which date back to the earliest days of the Milky Way, between 11 and 13 billion years ago. Stars like this have been observed for most of the history of the universe.
Star seeds
Nebulae are breeding grounds for the formation of new stars
By weight, most of Earth is made up of chemical elements heavier than helium, which are made in the cores of stars. This process is known as nucleation. During the lifetime of a star, nuclear reactions combine light elements and produce heavier elements. In this way, elements such as carbon, oxygen, silicon, sulfur and iron are formed in the hearts of stars. When stars run out of fuel, they throw the elements they made back into the universe.
Stars fill the galaxy with elements by their birth and death over billions of years. Carbon, oxygen, and nitrogen are among the most abundant elements made by smaller stars. As these stars die, their outer layers form a stellar nebula. From this example, we can refer to the Southern Ring Nebula, whose image was published by the James Webb telescope.
The life of the biggest stars also ends in a supernova explosion. These explosions not only fill galaxies with heavy elements such as iron, but their shock waves can be the basis for the birth of new stars.
The oldest known star
The oldest star in the universe was formed only 100 million years after the Big Bang
The hunt for the oldest stars in the universe is one of the fascinating fields of astronomy that can help scientists understand the early days of the universe. The oldest star ever discovered is HD 140283. The star is so old that the first estimates of its age are older than the universe itself. However, this effect is an illusion caused by the uncertainty in the estimates. Therefore, measuring the age of a star is not an easy task.
According to another research in the Journal of Astronomy and Astrophysics, the age of HD 140283 was estimated to be almost the same as the age of the universe, i.e. 13.7 billion years. In other words, this star was probably born a hundred million years after the Big Bang, and thus it is one of the first generation of stars that were born in the world. This star is metal-poor, or in other words, has a small number of chemical elements heavier than helium, and thus it is placed in the category of population 2 stars. Such stars are among the oldest objects that have ever shone in the universe. Based on the ratio of chemical elements, these stars are survivors of early stars from the early days of the universe.
The oldest known planet
The oldest planet in the world is nearly 12.7 billion years old.
No one knows exactly when the first planets formed, but they seem to be able to outlive stars. The oldest known planet orbits two dead stars, one of which is a pulsar and the other a white dwarf. Both stars are stellar wrecks that have run out of fuel and have released much of their chemical material into their galaxy. The mentioned pulsar is called PSR B1620 and the planet located in its orbit is known by the nickname Methuselah. This planet, which is a kind of gas giant, is not unlike the planet Jupiter.
According to estimates, the lifespan of Methuselah reaches 12.7 billion years, but this age is not exact. There is no good way to estimate the age of planets, so this estimate is based on other stars in the Methuselah cluster. Globular clusters, such as the Methuselah host cluster, are full of stars that formed at the same time.
According to the research of Science magazine, the existence of the ancient planet Methuselah offers interesting hints about the time of formation of the oldest planets. If the estimates are correct and Methuselah is really 12.7 billion years old, we can say that the planets were formed earlier than we think. In other words, Methuselah may not be the only ancient planet in our galaxy.
The formation of galaxies
Galaxies usually come together in several clusters
When the universe was only 200 million years old, the first galaxies were formed. The discovery initially surprised astronomers because they thought galaxies formed much later. Early galaxies were not similar to today’s massive galaxies. Rather, they were shapeless clouds of irregular gas and dust. These galaxies, accompanied by a wave of star birth, eventually became the massive galaxies that fill the universe today. It seems that the Milky Way galaxy was formed approximately 13.6 billion years ago. Our galaxy was then an unrecognizable mass of stars, not unlike the present spiral.
The oldest galaxy ever discovered was formed 300 million years after the Big Bang. This galaxy is called HD1 and the James Webb telescope played an important role in determining its age. HD1, if confirmed, would be the oldest galaxy ever seen by astronomers and could offer fascinating insights into the formation of the universe’s first galaxies. The formation of galaxies is still a mysterious research field full of unanswered questions. Helping to solve these questions will be one of the main goals of the James Webb telescope.
Large-scale structures of the universe
Galaxies are held together by gravity and form large-scale cosmic structures
Much of the world seems to be an empty void, But the universe has complex structures on very large scales. The universe is covered with an array of dark matter filaments that form a web-like structure. This network of dark matter, called large-scale structure, shapes the universe and causes galaxies to fall into regular patterns. The gravity of the large-scale structure causes both dark and visible matter to lie next to each other. By examining this structure, we can find signs of the youth of the world.
Deep background images, such as the James Webb Telescope image, can reveal how galaxies fit together. These structures are actually the largest visible structures or galaxy strings in the universe, held together by gravity. In addition, the structures are not random but have an order that still fascinates researchers. Galaxies and large galaxy clusters appear to be evenly spaced in the galactic strings, resembling a pearl necklace. There are still many uncertainties about large-scale structures.
Collision of galaxies
Some galaxies collide and form larger galaxies.
Gravity pulls everything in the universe together, and the heavier the mass, the greater this attraction. Galaxies are among the heaviest objects in the universe, whose formation and evolution are still a matter of discussion and their evolution is strongly influenced by their interaction with each other.
Galaxies usually tend to form groups or clusters that come together due to gravity and start interacting when they are close to each other. The gravitational pull of galaxies leads to the creation of lethal forces. In the most dramatic examples, galaxies can collide and their merger may take billions of years.
Galactic collisions can lead to the formation of new stars; Because the change of gravitational forces causes disturbances on huge scales. Some stars are ejected into the dark intergalactic space, while others are trapped by the gravity of supermassive black holes at the center of colliding galaxies. As the galaxies merge, their spiral arms are eventually destroyed, and the two galaxies eventually become one massive elliptical galaxy. In this way, some of the largest galaxies in the universe are formed. Some galaxies also grow by absorbing smaller galaxies. According to some evidence, the Milky Way has experienced such a collision in the past, and its signs can be seen in the form of remnants of galaxies that it has absorbed in the past.
History of the world
Massive black holes
Quasars are caused by the feeding of the black hole from the surrounding matter.
The largest galaxies, such as the Milky Way, have a supermassive black hole at their center; Although how these black holes formed is still a mystery, it is clear that they are very old. The European Space Agency has released an image of an ancient galaxy known as UDFj-39546284, which appears to be a small red dot in the image. This spot is actually the oldest quasar observed by astronomers and dates back to 380 million years after the Big Bang.
Quasars are among the brightest objects in the world, which are created by the feeding of the supermassive black hole at the center of a galaxy from the surrounding material. The big question here is how these black holes have reached these dimensions at a high speed. According to a study published in the journal Nature, supermassive black holes appear to have formed suddenly from turbulent cold gas in the early universe. In the right conditions, black holes were formed with great intensity and suddenly as a result of the collapse of streams of initial materials grew to dimensions exceeding 40,000 times the mass of the Sun.
The formation of the Milky Way disc
In the first 3 billion years of its existence, the Milky Way had no spiral arm.
Today, the Milky Way is a spiral galaxy, but it hasn’t always been this way. The spiral galaxy formed in a galactic disk, but the Milky Way disk formed about ten billion years ago. This means that our galaxy spent its first three billion years without a disk and therefore had no spiral arm.
The disk of a spiral galaxy contains a large part of the material of that galaxy. In such galaxies, star birth often occurs in spiral arms, as stars are formed from vast clouds of gas and dust slowly swirling around the galactic core. How and why spiral arms and disks are formed is still not completely clear, although this phenomenon has been observed frequently in the sky.
Some galactic disks appear to be very old. The oldest galactic disk ever seen is the Wolf disk. This old spiral galaxy dates back to when the universe was only 1.5 billion years old. Of course, due to the distance of this galaxy, we have no information about its new appearance.
Overcoming dark energy
Mysterious dark energy is responsible for accelerating the expansion of the universe.
One of the milestones in world history can be related to dark energy; The mysterious force that controls the expansion of the universe. No one knows exactly what dark energy is, although astronomers can measure its effects. Until a long time ago, the universe was in a tug-of-war between the force of gravity and the repulsive force of dark energy. At some point around 5-6 billion years ago, dark energy won the race. As the universe continued to expand, dark energy overcame gravity and accelerated the expansion of the universe.
The effect of dark energy on the future of the universe is still unclear. Without knowing more about dark energy or how it works, there’s no way to know. Although dark energy appears to make up a large part of the universe, its specifics are still shrouded in mystery. According to a possibility, this energy can be one of the inherent characteristics of space itself.
The birth of the sun
The sun was formed about 4.6 billion years ago from a cloud of gas and dust.
The sun is almost a third of the entire universe. This star was formed about 4.6 billion years ago. With the formation of the sun, the clouds of gas and dust around it formed planets such as Earth and many moons of the solar system.
The sun is one of the population’s 1 stars. Such stars are among the newest stars in the universe and are rich in heavy elements, examples of which can be found on Earth. According to a hypothesis, the shock wave resulting from a supernova was the cause of the formation of the solar system from vast dust clouds. The traces of this supernova exist in the form of radioactive isotopes in the entire solar system; So a star died so we could live.
The formation of the earth
Earth was formed from the joining of asteroids.
According to scientists, the story of the formation of the earth goes back to 4.6 billion years ago. Our planet formed in a disk-like cloud of gas and dust around the primordial Sun. Inside this disk, gas and dust particles of different sizes were rotating at different speeds in the orbit of the sun and in this way, they collided and stuck to each other. Finally, the tiny particles turned into huge rock fragments and objects called asteroids, whose diameters ranged from one to hundreds of kilometers.
Asteroids eventually gained enough gravity to clear their orbits and attract other bodies through collisions, becoming larger bodies several thousand kilometers in diameter and forming planets.
The first forms of life
The first life on earth dates back to 3.7 billion years ago.
Life on Earth is the only life we know of in the entire universe. Life first appeared about 3.7 billion years ago, shortly after the formation of the Earth itself. Thus known life is roughly a quarter of the age of the universe, although the complex life that would eventually become humans is much more recent.
Carbon is an essential element for life and appears to have been unavailable until 1.5 billion years after the Big Bang. For this reason, it is still not possible to estimate with certainty the first form of life in the entire universe. Maybe other parts of the world have different chemistry or different elements than life on Earth.
Extraterrestrial life and alien civilizations
Life in other parts of the world may be chemically different from life on Earth.
To quote the late astronomer Carl Sagan, “We are a way of knowing the world.” Humans are part of the world like the most distant stars or galaxies. In other words, at least a part of the world is capable of thinking and observing other parts. The oldest early humans appeared on earth approximately 2.4 million years ago; This means that humans and our direct ancestors only existed in 0.02% of the entire history of the world. On a cosmic scale, it seems like we were born just yesterday. However, humans may not be the only civilization in the world.
The question about the existence of other civilizations in the galaxy has a long history. Half of all Sun-like stars could host habitable universes; Therefore, there is no shortage for the formation of civilizations. According to a relatively conservative study, there should be at least 36 space civilizations capable of communicating in the Milky Way. According to another research, there are more than 42 thousand civilizations in the Milky Way. Currently, there is no way to find out the existence of these civilizations. With more accurate telescopes, we may be able to find evidence that we are not alone in this infinite universe.
Galaxies; everything you need to know
If you look at the night sky with a telescope, you will see many bright spots, many of which are actually galaxies. Galaxies come in all shapes and sizes, and almost every one contains billions of stars and supermassive black holes at their center.
What is a galaxy?
How did galaxies form?
Types of galaxies
Evolution of galaxies
Collision of galaxies
Active galaxies
The number of galaxies in the universe
Galaxies and dark matter
The strangest galaxies
The closest galaxy to the Milky Way
The Milky Way
Observing galaxies
What is a galaxy?
A galaxy is a collection of millions and even trillions of stars, gas, dust, and dark matter that are held together by gravity. Small galaxies known as dwarf galaxies have only a few hundred million stars, while huge galaxies have up to one hundred trillion stars, all of which revolve around the center of mass of the galaxy. Galaxies come together in groups called galaxy clusters, which range from hundreds to thousands of galaxies.
How did galaxies form?
Astronomers are not sure how galaxies form. After the Big Bang, space was a mixture of two elements, hydrogen and helium. Some astronomers believe that gravity attracted gases and dust towards each other and the first stars were born; Then these stars formed clusters called galaxies. Another group thinks that the mass of galaxies came together before the formation of stars inside them. Almost all large galaxies contain supermassive black holes at their centers.
By examining the past, scientists can simulate how galaxies formed in the early universe and how they grew. Astronomer Edwin Hubble came up with the idea of an expanding universe with his observations. According to the estimates and the speed of expansion, 13.8 billion years have passed since the age of the universe. Although most of the galaxies were formed at the beginning of the universe, the data show that some galaxies were formed in the last few billion years and in the distance from the Big Bang.
Although the Hubble telescope is not able to see the first galaxies; it can track the growth of galaxies on cosmic time scales. Hubble images and other sky maps show that galaxies are located at very different distances from the universe and therefore are in different stages of their growth.
This supercomputer simulation shows the formation of galaxies similar to the Milky Way around 7.13 billion years ago.
Types of galaxies
After discovering the galaxies, Hubble and other researchers studied them more closely. This was very difficult for the 1920s. At that time, recording just one image or galaxy spectrum required a full night of uninterrupted observation. Today, large telescopes and electronic detectors have made this difficult task easier, although observing distant galaxies requires considerable effort.
The first step to understanding the type of crime is to define it. The largest and most complex galaxies usually have one of two basic shapes: they are flat like the Milky Way and have a spiral arm, or they appear elliptical. On the other hand, many smaller galaxies have an irregular shape. The following table lists some of the most famous galaxies and their types:
Spiral galaxies
The Milky Way and Andromeda are both large spiral galaxies. These galaxies have a swollen central halo, a disk, and spiral arms. Interstellar material is scattered between the disks of spiral galaxies. Bright nebulae and hot young stars are located in the spiral arms, showing that stars are still being born. Discs are usually dusty.
Open star clusters can be seen in the arms of the closer spirals, and globular clusters can be seen in the halo. Spiral galaxies are a mix of young and old stars. About two-thirds of nearby spiral galaxies have peanut-shaped, box-shaped stellar bars that orbit the center. The Milky Way also has a bar. Spiral arms start rotating from the end of the rod. In barless and barred spiral galaxies, we see a variety of shapes.
Image of barred spiral galaxy NGC 1300 captured by the Hubble Space Telescope
The diameter of the bright parts of spiral galaxies varies from 20,000 to more than 100,000 light years. New research suggests that galactic material may flow beyond the edge of the galaxy. These materials are cold and thin gases that are difficult to detect in observations.
According to the available data, the mass of the visible parts of spiral galaxies varies between 1 billion and one trillion solar masses. The total luminosity of most spiral galaxies is between 100 million and 100 billion times that of the Sun. The Milky Way and the M31 (Andromeda) galaxies are considered large and massive spiral galaxies. There is also a significant amount of dark matter in and around galaxies; It is possible to find out the existence of dark matter based on the speed of movement of stars in the outer parts of the galaxy.
Vortex non-barred spiral galaxy and its accompanying satellite galaxy
Elliptical galaxy
Elliptical galaxies are composed almost entirely of old stars and are spherical or elliptical in shape (compacted spheres). These galaxies lack a spiral arm. Their light comes from old red stars or population 2 stars. In larger elliptical galaxies, many globular clusters are seen. Nebulae and dust are not prominent in elliptical galaxies, But they have a small amount of interstellar matter.
The degree of width of elliptical galaxies is different from each other. Some of them are nearly spherical systems like flat spiral galaxies. Giant elliptical galaxies are more than a few hundred thousand light-years in diameter and are significantly larger than spiral galaxies. Although the stars rotate independently around the center of the elliptical galaxy, their orbits are not in the same direction as in the spiral galaxy. As a result, elliptical galaxies do not rotate regularly, and for this reason, it is difficult to estimate their dark matter.
The dimensions of elliptical galaxies vary from giant galaxies to dwarf galaxies. Leo I is an example of a dwarf elliptical galaxy. The brightness of this type of dwarf is almost equal to the brightest global clusters. An intermediate galaxy between giant and dwarf systems such as M32 and M110 are the two companion galaxies of Andromeda. Although these galaxies are classified as elliptical dwarfs, they are significantly larger than galaxies like Leo I.
The giant elliptical galaxy ESO 325-G004
Irregular galaxy
Hubble classified the galaxies that do not have a regular shape in the irregular galaxy group. Irregular galaxies usually have less mass and luminosity than spiral galaxies and are disorganized. These galaxies contain young population of 1 star and an old population of 2 stars.
The galaxy NGC 1427A is an example of an irregular galaxy at a distance of 52 million light-years
Two examples of the most well-known irregular galaxies are the Small Magellanic Cloud and the Large Magellanic Cloud, which are located at a distance of slightly more than 160,000 light years and are among the closest extragalactic neighbors. The names of these galaxies are a symbol of Ferdinand Magellan and his crew’s journey around the world. They were the first Europeans to see the Magellanic Cloud in the night sky. Although these two systems are not visible from Europe and the United States, they are easily visible in the night sky from the Southern Hemisphere. The Magellanic Clouds provide astronomers with an excellent opportunity to study nebulae, star clusters, variable stars, and other key galactic objects.
A wide view of the Large Magellanic Cloud
The Small Magellanic Cloud is much less massive than the Large Magellanic Cloud and is six times as long as it is wide. This narrow strip is like an arrow towards our galaxy. The Small Magellanic Cloud has taken its current form due to the gravitational interaction with the Milky Way. A huge string of pebbles resulting from this reaction are stretched in the night sky and can be seen inside the gas clouds that move at a high speed. This set is called the Magellanic string. Based on the interaction of galaxies, the irregular shape of smaller galaxies can be justified.
Evolution of galaxies
Astronomers can relate the differences in the appearance of galaxies to their evolutionary stages. For example, could an elliptical galaxy have evolved into a spiral? Since no simple plan has been found for the evolution of one particular type of galaxy into another, astronomers have come up with another view.
For a while, astronomers thought that all galaxies formed early in the history of the universe and that the difference between them was rooted in the rate of star formation. Elliptical galaxies were galaxies in which all of their stellar material quickly turned into stars. While the process of star formation in spiral galaxies has been slower.
Today we know that at least some galaxies have evolved over billions of years since the beginning of the universe. Galactic collisions and mergers can transform spiral galaxies into elliptical galaxies. Even isolated spiral galaxies with no neighboring galaxies evolve over time, and as the rate of star formation slows down, the spiral arms shrink over time. During the last decades, studying the evolution of galaxies and the universe has become one of the hottest research topics in astronomy.
Collision of galaxies
Despite the great distance, unlike stars, galaxies can approach each other, affect each other, or even collide. When galaxies collide, they actually pass through each other; Their stars do not collide with each other due to their great distance. However, gravitational effects between colliding galaxies can lead to new waves of star formation, supernovae, and even black holes. Collisions change the shape of galaxies, and based on computer models, the result of the collision of spiral galaxies can be an elliptical galaxy.
In the next four billion years, the Milky Way will collide with the Andromeda Galaxy
In the next four billion years, the Milky Way will collide with its spiral neighbor Andromeda. The sun will probably wander, But it does not threaten the earth and the solar system. Andromeda, also known as M31, is 2.5 million light-years away from Earth, but it is moving towards the Milky Way at an incredible speed due to the common gravity between the two galaxies and the dark matter that surrounds them both.
Computer simulations of the Hubble data show that after the two galaxies approach, it will take two billion years for both galaxies to completely merge due to gravity. The Milky Way and Andromeda will form an elliptical galaxy after merging, which is one of the most common examples in the universe. According to the simulations, the solar system will probably move away from the center of the galaxy after the collision.
This firestorm in the sky is the result of the collision of two spiral galaxies that started around a few hundred million years ago. This collision has caused the compression of huge clouds of gas and dust and the beginning of a new wave of star births in the galaxy.
Active galaxies
Some galaxies are classified as active galaxies if they contain an active galactic nucleus (AGN). In these galaxies, instead of stars, gas, and interstellar matter, a significant part of the energy is emitted by the galactic nucleus. There are several types of AGNs; But the nuclei that are in the low brightness spectrum are called Seyfert galaxies, while the nuclei with more brightness than the host galaxy are called quasi-stellar objects or quasars.
AGNs emit radiation across the electromagnetic spectrum and X-ray radio wavelengths. The standard model of the active galactic core is based on the accretion disk that forms around the supermassive black hole in the core of the galaxy.
Active galactic core rays are the result of the gravitational energy of matter falling into the black hole from the disk. AGN luminosity depends on the mass of the supermassive black hole (SMBH) and the rate at which matter is infalling into it.
UGC 6093 is classified as an active galaxy, which means it hosts an active galactic nucleus.
Blazers and quasars
Ballars and quasars are two examples of common AGNs. A quasar is an active galactic nucleus that emits streams of particles outward from the center of the galaxy. The difference between quasars and blazars is their angle. The closest quasar to Earth is Markarian quasar 231 in the constellation Ursa Major. Quasars are so distant that they are thought to be from the early stages of the galaxy.
What is a quasar?
A quasar is only one type of active galactic nucleus, which includes blazars, radio galaxies, and Seyfert galaxies. The full name of a quasar is a quasi-stellar radio object. Quasars are actually supermassive black holes active in the center of galaxies, and they shine more than stars in the galaxy. These objects have an accretion disk of gas and dust and release electromagnetic radiation as matter falls into the quasar. Quasars are disabled after taking the augmentation pill. These objects are usually located in the center of distant galaxies.
All the quasars that have been seen so far are billions of light-years away from Earth, that’s why many scientists believe that these objects are the core of young galaxies. If we can see these objects today, they are probably completely calm, and like any other galaxy, no flow can be seen from them.
Quasar Markarian 231 in the constellation Ursa Major
What is a blazer?
The difference between a quasar, a radio galaxy, and a blazar is in the angle of their flow. If the flow is upward, it is a radio galaxy, if the angle has a slight deviation, the object is a quasar, and if the flow is completely in our direction, the object is a blazar.
The number of galaxies in the universe
It seems impossible to count all the galaxies. One of the problems is instrumental limitation. To achieve the best view, telescopes need a large aperture (the diameter of the main mirror or lens) and must be placed outside the Earth’s atmosphere to avoid distortion.
According to Mario Livio, an astrophysicist at the Space Telescope Science Institute in Baltimore, Maryland, the acceptable range of galaxies varies between 100 billion and 200 billion, although each expert offers several estimates. With the launch of the Jamesob telescope, it is expected that more information about the early galaxies of the universe will be obtained.
Regardless of the tool used, the method of estimating the number of galaxies is the same. The telescope takes pictures of a part of the sky. The total number of galaxies can then be estimated based on the obtained fraction.
Measuring the expansion of the universe shows that the age of the universe is approximately 13.8 billion years. As the age of the universe increases and those galaxies become larger, they become further away from each other. As a result, it becomes more difficult to see them with a telescope. This is where the visible world hypothesis comes into play. According to scientists, in the next one to two trillion years, the galaxies will go beyond the range of the Earth’s vision.
Galaxies also change over time. For example, as we said in the previous section, the Milky Way galaxy will collide with the Andromeda galaxy in the distant future, and both will merge within 4 billion years. The inhabitants of distant galaxies will face the world of darkness.
Galaxies and dark matter
In the late 1970s, astronomer Vera Rubin discovered dark matter. He was studying the rotation of galaxies when he noticed the strange rotation of Andromeda. The speed of the materials at the edge of the galaxy was as high as the materials in its center, and this phenomenon undermined Newton’s and Kepler’s laws. Although much of the mass was concentrated in the center; an invisible mass called dark matter seemed to hold the galaxy together. Rubin soon discovered a huge halo of dark matter in the Andromeda galaxy.
Although almost half a century has passed since this discovery, no one still knows what the nature of dark matter is. However, this strange and invisible matter makes up nearly 84% of the mass of the universe, and its pervasive presence affects stars and galaxies and the density of matter in the early universe.
Some of the best evidence for dark matter comes from the galaxy cluster 1E 0657-556, or the Bullet Cluster. This cluster was formed by the collision of two larger galaxy clusters, the most energetic event since the Big Bang. Because the main parts of the cluster pair, the stars, gas, and dark matter, behaved differently during the collision, scientists were able to study them separately.
The stars of the globular cluster galaxies observed by the Magellan and Hubble telescopes in visible light were not affected by the collision and passed by each other. The hot gas from the collision of the two clusters was observed at X-ray wavelengths by the Chandra X-ray Observatory. This gas contains a large fraction of the normal matter of the cluster pair. Because the gases react electromagnetically with each other, the gas of both clusters has a slower speed than the stars. The third element of this collision, i.e. dark matter, was also discovered indirectly using the gravitational lensing of background objects.
By definition, dark matter does not have any electromagnetic reaction, especially light reaction. This material is dark as its name suggests. As a result, the masses of dark matter of the two clusters passed by each other like stars during the collision and left behind hot gas. If the hot gas was the most massive material of the clusters, the gravitational lensing effect would not be seen. As a result, these observations were the first evidence to prove dark matter.
The strangest galaxies
According to estimates, the universe consists of 100 to 200 billion galaxies. We will certainly face many wonders in such a large collection. From mermaid-like galaxies to galaxies with dead stars. Below we mention some of the strangest galaxies.
Mermaid Galaxy
Located in the constellation of the Southern Triangle, ESO 137-001 looks like a starfish swimming in a sea of stars. This galaxy is a barred spiral galaxy. In addition to the bar, there are twists and trails in this galaxy. These trails are streams of stars that appear to be deflected from the galaxy like the tails of mermaids.
According to NASA, these stars form a tail of gas and dust that flows outward from ESO 137-001. The formation process of this galaxy remains a mystery because the gases inside the tail must be hotter than these for star formation.
Zombie galaxy
The rotation speed of a massive disk galaxy like MACS 2129-1 is twice that of the Milky Way, But it is not as active as that. Hubble’s observations of this distant galaxy show that no new star has been born in this galaxy since 10 billion years ago.
MACS 2129 is also known as a dead galaxy because there are no new stars in this galaxy. According to scientists, such galaxies may have been formed over time due to the merger of smaller galaxies; But the stars in MAC 212901 are not the result of explosive mergers, but were formed in the main disk of the galaxy. The findings of this research show that dead galaxies change their internal structure because they merge with other galaxies over time and their shape changes.
Gay galaxy
Some galaxies are cannibals. The Andromeda Galaxy, Earth’s closest neighbor, has been swallowing other galaxies for the past ten billion years. This galaxy and the Milky Way will collide in about 4.5 billion years, although by then the Sun will reach the end of its life, and life on Earth will become impossible.
Frog floating in space
Three hundred million light years away, a giant frog swims in space. The Frog Galaxy has a tail that is 500,000 light-years long and ten times longer than the Milky Way; But what caused the formation of this strange galaxy? According to researchers in 2018, a cosmic collision is the cause of this strange shape. Two galactic disks are stretched over a smaller dwarf galaxy so that stars are piled up on one side of the head of the galaxy, and on the other side is a long tail.
Brilliant thief
Galaxies are constantly interacting with each other, changing the shape of their neighbors, stealing stars, and doing other mischief. The brightest known galaxy in the universe is one of these thieves. In 2018, scientists reported the observation of the galaxy W2246-0526, which has stolen half of the mass of its three neighboring galaxies.
Little lion cub
Probably the cutest galaxy is the Little Lion Cub in the constellation Ursa Major. This dwarf galaxy has been inactive since the Big Bang, meaning it contains unchanged molecules from moments after the Big Bang explosion, about 8.13 billion years ago. The little galactic lion cub is doomed; Because a spiral galaxy called NGC 3359 is devouring its material. However, it is possible to understand the effects of the molecules of the early universe by examining the flow of its stellar gases.
Blooming galaxy
The galaxy ESO 381-12 appears to be flourishing. This galaxy is located at a distance of 70 million light-years from Earth in the constellation Centaurus. This galaxy is a lenticular type, which is a combination of a spiral galaxy like the Milky Way and an elongated elliptical galaxy. What makes this galaxy strange are the uneven petal-like blooms that extend outward from the main body of the galaxy. Astronomers are not entirely sure what causes these structures, But the blooms may be shock waves from a cosmic collision that set the stage for new tectonics to form.
Beautiful spiral
Messier 83 is a massive spiral galaxy with a bar-shaped center similar to the Milky Way. This galaxy is located at a distance of 15 million light-years from Earth in the constellation of the Serpent. Messier 83 is strange in several ways. It primarily has a dual-core in the center. It seems that two supermassive black holes are located in the center of this galaxy.
Secondly, it is full of supernovae. Astronomers have so far identified six of these stellar explosions and the remnants of more than 300 of them. In this way, track 83 ranks second in terms of the number of supernovae after the galaxy NGC 6946, which has the highest number of recorded supernovae.
Cosmic vermin
This image seems to be of a dandelion rather than a cosmic phenomenon. This image, recorded by the Hubble Space Telescope, belongs to a galaxy called the Bug; Because its light jets prevent it from examining nearby stars.
Eye galaxy
The disk of the spiral galaxy IC 2163 appears to be scanning the sky with a large eye. This eye-like galaxy is actually a huge string of stars and dust. According to astronomers, these eye features only last for a few million years, which is based on the lifespan of galaxies like the blink of an eye.
The researchers found that the characteristic optical gases are moving towards the center of IC 2163 at a speed of 100 km/s and become more disordered and slower as they approach the center of the galaxy. The deceleration causes the gas to gather and compress, which itself provides the basis for the formation of new stars.
Two hearts
Most galaxies probably have a massive black hole in their center, But some of them also have two black holes. One of these galaxies, NGC 7674, is a spiral galaxy centered on two supermassive black holes, one light-year apart. This galaxy probably absorbed its black hole during a merger with another galaxy. The only other known galaxy with two central black holes is the massive galaxy 379+0402.
The galaxy has stopped
If you are a galaxy, you will probably either swallow other galaxies or die. The galaxy NGC 1277 chose the latter. This galaxy, which was first observed in 2018, is 240 million light-years away from Earth. During the last ten billion years, no new stars have been formed in this galaxy and therefore it is considered a dead galaxy.
Astronomers believe that NGC 1277 is so amazing that it is moving at such a high speed to swallow up other galaxies. This galaxy moves in space at a speed of 3.2 million kilometers per hour. NGC 1277 would not be able to form stars without the gas and dust of other galaxies. Some astronomers think that most galaxies look like NGC 1277 and have grown through mergers with other galaxies.
A galaxy on our way
According to scientists, most galaxies are moving away from Earth because space is continuously expanding; But Messier 90 is not like this. This spiral galaxy, which is 60 million light-years away from Earth, is moving in the direction of the Milky Way.
Astronomers can measure the galaxy’s motion because its light is deflected toward the blue end of the light spectrum. Objects moving away from Earth tend to be red, that is, their light emission goes towards the red. Messier 90 is part of a large group of galaxies called the Virgo cluster. This galaxy can be seen in May with a telescope or binoculars in the Northern Hemisphere between the constellations of Virgo and Leo.
The closest galaxy to the Milky Way
Small galaxies like the Large and Small Magellanic Clouds are among the closest galaxies to the Milky Way. Although many small and dwarf galaxies are close to the Milky Way, the Andromeda Galaxy is the closest large spiral galaxy to the Milky Way. The Andromeda Galaxy is the brightest object in the night sky, located 2.5 million light years from Earth; It means the farthest thing that a human can see with the naked eye.
Astronomers sometimes call Andromeda Messier 31 or M31. Andromeda is the 31st object in the famous list analyzed by the French astronomer Charles Messier (1817-1731). Today, amateur astronomers can see these galaxies with telescopes and binoculars. The diameter of Andromeda, like the Milky Way, reaches 100,000 light years.
The Milky Way
The Milky Way galaxy is our home and for this reason, it has the greatest research importance. Looking at the night sky, you can see a band of light that many ancients called a river, lion, or path. This attractive line of light is actually the center of the Milky Way as seen from its outer arms.
Understanding the structure of the Milky Way is a bit challenging. The solar system is located right at the outer edges of one of the arms of the Milky Way. The position of the Sun in the galactic disk surrounded by dust is one of the obstacles to observing the structure of the Milky Way. The Milky Way is a spiral bar with a diameter of 100 thousand light years. If you look at it from above, you will see a central bulge surrounded by four large spiral arms. Spiral galaxies make up two-thirds of the galaxies in the universe.
A barred spiral galaxy, unlike a normal spiral galaxy, contains a bar-like structure in the central part and has two main arms. The Milky Way has two small arms as well as two smaller sequences. One sequence, called the Orion arm, contains the Sun and the Solar System. Orion’s arm is located between the two big arms of Perseus and Sagittarius.
The Milky Way is continuously rotating. Its arms move in space and the sun and the solar system move along with it. The solar system moves through space at an average speed of 828,000 kilometers per hour, and even with this high speed, it takes 230 million years to travel the entire Milky Way.
The arc of the Milky Way in the expanse of the night sky. This composite panorama image was recorded at the Paranal Observatory in northern Chile
The Milky Way is surrounded by a huge halo of hot gas that stretches for hundreds of thousands of light years. This halo of gas is as heavy as all the stars in the Milky Way and is rotating at a high speed like the Milky Way itself. The spiral arms around the center of the galaxy contain large amounts of gas and dust. New stars are continuously formed in these arms. These arms are called galactic disks. The thickness of the galactic disk is only 1000 light years.
In the center of the galaxy is the galactic bulge. The heart of the Milky Way is full of gas, dust, and stars. The gas and dust in this bulge is so thick that you cannot see beyond it. According to the hypotheses, there is a supermassive black hole at the center of the Milky Way, which is billions of times heavier than the Sun. This megamass black hole was initially small, But it grew bigger over time by feeding on the surrounding gas and dust. Although black holes cannot be seen directly, they can be identified based on the traces they leave behind. Most galaxies in the universe contain a black hole at their center.
The solar system is located at a distance of 30 thousand light years from the center of the Milky Way
The Milky Way contains more than 200 billion stars, and there is enough gas and dust in it to give birth to billions more. The solar system is just 30,000 light-years away from the center of the Milky Way and 20 light-years above the galactic plane. Earth and its neighbors are not in the galactic plane and have a 63-degree deviation from it.
More than half of the stars discovered in the Milky Way are older than the Sun, which is 4.5 billion years old. Galaxies like the Milky Way typically undergo star birth explosions about ten billion years ago. At that time, a huge collection of stars were born. The most common stars in the Milky Way are red dwarfs. Cool stars that have one-tenth the mass of the Sun.
Observing galaxies
The Greek philosopher Democritus first proposed that the bright band of the night sky known as the Milky Way contained distant stars. However, Aristotle believed that the Milky Way was created by the burning of some huge stars. Ibn Haytham (1037-965 AD) made the first attempts to observe and measure the parallax of the Milky Way and concluded that since the Milky Way has no parallax, it must be very far from the Earth and does not belong to the Earth’s atmosphere.
Abu Rihan Biruni, an Iranian astronomer (1048-973) believed that the Milky Way is a collection of countless nebula-like stars. Ibn Bajah, an Andalusian astronomer, also believed that the Milky Way consists of many stars that are close to each other and look like a continuous image due to the phenomenon of light refraction.
Related articles: What happens when two galaxies collide?
The actual proof of the Milky Way was presented in 1610; That is when Galileo Galilei used a telescope to examine it and realized that the Milky Way is a combination of many faint stars. In 1750, the English astronomer Thomas Wright, in his work titled The Main Theory or The New Hypothesis of the Universe, correctly pointed out the rotating body containing countless stars that are held together by gravitational forces.
Modern research
In the early 1900s, many astronomers believed that the entire universe was located in the Milky Way galaxy. Others, such as Harlow Shipley, a scientist and head of the Harvard College Observatory, believed that there were spiral-shaped bubbles of gas and dust and called them island worlds.
It was in 1924 that Edwin Hubble first discovered some pulsating stars called Cephasian variables and realized that these stars are outside the range of the Milky Way. These astronomical objects were unique collections of stars far away from the Milky Way.
After measuring the distances, Hubble measured the Doppler effect, which is the stretching of the light of the galaxies due to motion. He discovered that the galaxies around the Milky Way are moving away from us at incredible speeds. The more distant the galaxies, the faster they escape. For this reason, Hubble noticed that the whole universe is expanding, and years later astronomers noticed the increase in the speed of this expansion.
Images recorded by the Hubble Space Telescope
Emerging galactic research
In recent years, astronomers have been tracking galaxies and their evolution with dark matter. Dark matter and dark energy together make up most of the mass and energy of the universe, But it is difficult to prove their existence because it is only possible to identify the traces they leave on other objects.
In 2017, astronomers discovered two massive galaxies from the ancient universe that formed in a sea of dark matter. The large size of these galaxies raised questions as to whether galaxies are getting bigger over time or whether another process is responsible for this phenomenon. Just a few months after the discovery, astronomers found a group of galaxies orbiting in sync in a pattern that can only be described by dark matter.
In 2018, after discovering a galaxy called NGC 1052-DF2, a group of researchers realized that the dark matter of this galaxy is 400 times less than the existing models, which could change the models of galaxy evolution. However, the results of this study are still controversial and under investigation. State-of-the-art galactic periodic maps have allowed scientists to identify galaxies that were difficult to observe in the past and gain more data about the evolution, size, and shape of galaxies.
What if Earth had rings like Saturn?
A ringed planet can make the night sky beautiful. To be honest, Saturn owes 90% of its beauty to its rings, otherwise, the planet itself has no significant atmospheric feature. The earth also has its beauties, But suppose our planet also has rings. Beauty should be in the eyes of the beholder, not in what is being looked at. However, have you ever wondered what would happen to the Earth if it had rings?
Rings are formed by solid objects that come too close to a planet. There is a range called the Roche limit, within which the gravitational forces of the main mass (in this example the Earth) are strong enough to disintegrate a moon. The limit of the method depends on the radius of the initial mass and the density of the two masses, and as a result, it is not a single value.
If we consider the Earth and the Moon based on the definition of the maximum limit, the Moon can approach the Earth up to a distance of 9,500 km in order not to collapse. If we want ice rings, we have to look for icy lunar destruction, which is possible for Saturn, not Earth.
The rings will be visible from different points on the ground, but their angle is different at each point
How to make a ring for the earth?
Suppose you want to give rings to the earth and keep the moon in its place. For example, you are looking for an icy ring like the rings of Saturn. The best way is to have an icy moon with the same density as Enceladus, Saturn’s moon. This moon must come close to the earth at a distance of 5300 km to disintegrate. On the other hand, you don’t need a moon as big as the moon for this. A large comet is enough to make a beautiful ring around the Earth.
However, the loop has a problem. Ice doesn’t last very well in Earth orbit. This is why the objects of the inner solar system are very dry. As a result, it might be better to settle for a stone ring, which is not as bright as the ice rings. However, the moon, which is completely rocky, reflects a tenth of the light it receives, enough to make bright rings.
To make the ring, an asteroid of suitable dimensions can be placed safely close to the Earth. The required raw materials can be found in a small mass and by placing it at the right distance, the desired goal can be reached. In this situation, the lethal forces do their work and over time a beautiful circle is formed. This method works for large and small crimes. Asteroids like Chariklo have rings that can last up to 10 million years.
In this mental experiment, things like the stability of the rings, the dimensions of the particles that make up the ring, and the existence of Shepherd’s moons are very important. Shepherd moons are small bodies that help balance the forces.
Saturn’s rings are not permanent features and will disappear one day
How to save rings?
Rings are not permanent. Saturn’s rings are only 400 million years old and maybe even younger. This time scale may seem very long to humans, but in the span of 4.5 billion years, it covers only 10% of the life of Saturn. As a result, this feature is temporary.
The destruction of rings also happens gradually. Some particles escape, but many fall on the planet itself as rain. The inner part of the rings also creates a permanent meteor shower that lands on the equator.
In Saturn, the gradual deterioration of the rings causes an increase in the temperature of a certain part of the upper atmosphere of this planet. There is a possibility of this happening to the earth as well. The lowest altitude for the rings can reach 1000 km. Particles below this height are quickly pulled down by the very thin atmosphere.
The consequences of the rain of rings are unclear, as we have not faced this issue in reality. Certainly, their continuous effect will be felt on the upper atmosphere, and of course, not only the equatorial regions will be affected by this event, because all parts of the world are connected with each other, and warming in the equator will affect the entire earth.
Looping seems to be a pain. If we want to witness such an event for a rocky planet, it is better to wait for Mars . In less than ten million years, Mars’ moon Phobos will be destroyed by this planet and a ring system will form around it, despite all the dangers and beauty.
What happens when two galaxies collide?
Gravity can make extraordinary things happen. This invisible force has a significant effect on cosmic matter. Gravity is the factor that transforms gas and dust into bright stars, transforms irregular rocks into spherical planets and finally collides galaxies with each other. Sometimes two galaxies, and sometimes more, move towards each other. This movement continues until the galaxies collide with each other. In this situation, the internal materials of the galaxies may collide with each other and combine, and as a result, the slow chaos turns them into a huge galactic ball.
Astronomers have observed such events known as mergers in the past. At the beginning of the encounter, it looks like the galaxies have gathered for a space conference. At the peak of this process, gravity distorts the shape of the galaxies, and at the end, an irregular sphere remains. Then the only sign of the merger is the faint flickering of stellar material around the galaxy.
The image below, taken by the Jumnai Telescope in Hawaii, shows the beginning of a merger in remarkable detail. The two galaxies NGC 4567 above and NGC 4568 below orbit each other, their stars pushing each other and new stars shining until everything merges in about 500 million years and the final shape is a heart in the sky.
Galactic mergers are among the most fanciful events in the universe. Supernovae and black holes definitely have their charms, But galactic mergers have a lot to say. These events also provide good grounds for daydreaming about extraterrestrial life. For example, consider NGC 4568 and NGC 4567, which are full of stars and most of the stars have planets based on the observations obtained; So maybe NGC galaxies are home to other beings; But what does it feel like to be in the middle of a galactic merger? According to Vicente Rodríguez Gómez, an astronomer at the National University of Mexico:
The night view in the merged galaxies will be very promising. The sky is filled with new stars, and the curved streams of stars, gas, and dust drawn across the sky can be clearly seen. The view of this sky will be especially spectacular if you live on the outer edges of the galaxy. In this situation, the night sky is not as crowded as the center of the galaxy.
Now suppose another galaxy merges with your galaxy in the outer domains. In this condition, this galaxy appears bigger and brighter than any other star in the darkness of the night. Even more exciting, you can view this sight almost without worry because the Sun is highly unlikely to collide with another star despite the collision of galaxies. Moya McTyre, astrophysicist and author of ” The Milky Way: A History of Our Galaxy ” says:
Have you ever seen a band of military musicians? Or a performance in which two groups walk through each other? Stars similarly move through galactic mergers, passing by each other like unison musicians. Although there are many stars, space is still infinite and most stars are not in danger of colliding with anything else.
Of course, if your planet is in a remote place, you may face a problem. The pressure from the collision can throw stars from the edges of a galaxy deep into intergalactic space. On the other hand, even though the stars regularly pass by each other, the space between them can be a little irregular. According to Jehan Kartaltep, an astrophysicist at the Rochester Institute of Technology and one of the researchers of the formation of galaxies:
Galaxies have huge clouds of gas and dust, and if they collide, these huge clouds of gas and dust collide with each other.
As a result, the collision process of gas and dust can create hazy masses of gas and dust in the night sky, which eventually collapse due to their own weight and form new stars. Astronomers on Earth can observe these starburst regions in galaxy merger images.
For example, consider the image below of the Hubble Space Telescope. This image shows the antennae galaxies, whose collision began approximately 600 million years ago, and as their spiral structures disappeared, new star clusters were formed, which can be seen as blue spots in the photo.
As the material of the merging galaxies migrates, the galaxies’ massive black holes also move and merge into the center of the new galaxy. In their path, these invisible heavy objects pull visible material such as meteors and stars towards them and possibly swallow some of them. Chiara Mingarelli, an astrophysicist at the University of Connecticut and the Flatiron Center for Computational Astrophysics who studies the fate of supermassive black holes in mergers, says:
When the merger of two galaxies begins, the supermassive black holes at their center are transferred to the center of the new galaxy and eventually merge with each other. In the example of three galaxies colliding, the most likely scenario is that two black holes will meet and form a binary system, and when the third black hole arrives, the less massive black hole may be ejected from the galaxy and eventually become a massive black hole wandering in the universe. .
All the above processes, such as the birth of new stars and the wandering of black holes, occur over millions or even billions of years. As a result, the hypothetical inhabitants of NGC galaxies do not see any changes during their lifetime but only know that they live inside a merger. Hypothetical astronomers of this universe could make classifications through archived observations of previous generations, collecting data for future scientists. Just as astronomers on Earth have calculated the Milky Way’s small mergers and the absorption of other small galaxies, hypothetical astronomers in the NGC could gain data about their galaxy’s past.
The Milky Way is on a collision course with another spiral galaxy called Andromeda. Today, Andromeda is seen as a dot in the night sky, but in five billion years, it will collide with our galaxy. The spiral arms of the Milky Way disappear, as does its supermassive black hole. Andromeda’s central black hole with a mass of 100 million solar masses will swallow our black hole with a mass of 4 million solar masses.
Artistic rendering of the collision between the Milky Way and Andromeda
Although galactic mergers do not lead to noticeable changes in a human lifetime, they are a great opportunity for the astronomers who live inside them. Being alone in an isolated galaxy might be a disadvantage. For example, Earth’s position in the Milky Way prevents astronomers from getting the best vantage points to study the Milky Way. There is also a lot of gas and dust on the way. McTyre says:
We should investigate other spiral galaxies to learn about the behavior and evolution of the galaxy we live in; But if there is another spiral galaxy near us and its angle is such that a large part of it can be seen, it can be studied much easier than our own galaxy.
On the other hand, being an astronomer in the middle of a galactic merger is a bit boring; Because in such conditions, the night sky is very crowded and it is not possible to examine distant objects. According to Rodríguez Gomez: “In such an environment, it is difficult to find a path without light pollution.”
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