A virtual simulation illustrating the collision between a massive galaxy resembling the Milky Way and a smaller dwarf galaxy. Scientists hypothesize that the Milky Way experienced at least one such collision during its creation.
The Koisan people from Black Africa, observing the meandering band of stars and particles that divides the nocturnal heavens, interpreted it as a smoldering fire. Polynesian seafarers perceived a shark devouring clouds in the celestial sphere. The ancient Greeks witnessed a cascade of milk and named this pathway “milky” – galaxias – thus giving rise to the term “galaxy”.
In the 20th century, astronomers ascertained that our shimmering river is merely a fragment of an immense constellation of stars, subsequently penning their own chronicle of the origin of the Galaxy [when it became evident that the Milky Way is not the sole galaxy, the word “Galaxy” with a capital letter was retained as an alternate proper name for the Milky Way]. In a nutshell, the Milky Way came into being approximately 14 billion years ago through the fusion of colossal masses of gas and particles under the influence of gravity. As time elapsed, two distinct structures materialized – initially a vast spherical “halo” and subsequently a dense, luminous disk. Billions of years transpired, and within the disk, our own solar system emerged. And now, gazing skyward during the night [in a region with relatively minimal light pollution / note], we behold a spilled milk – or a ribbed disk stretching across the firmament.
However, over the past couple of years, scientists have completely reworked nearly every significant aspect of the history of the Milky Way. What caused this shift? It can be attributed to the acquisition of higher quality data.
On April 25, 2018, the Gaia spacecraft from Europe released an overwhelming amount of information about the celestial sphere. The most noteworthy aspect of this data was the detailed descriptions of the movements of approximately one billion stars, collected by the spacecraft over the span of a year. Previous studies had only examined the motions of a few thousand stars. These discoveries have breathed new life into what was once a static galaxy. “Gaia has sparked a new revolution,” remarked Federico Sestito, an astronomer at the Strasbourg Astronomical Observatory in France.
Astronomers were quick to retrieve a dynamic star map, leading to a flood of new findings. One remarkable discovery was the presence of incredibly ancient regions within the disk. Additionally, evidence was uncovered indicating that the Milky Way experienced intense collisions during its early, turbulent phase, and there are indications that the galaxy remains in a state of constant, unexpected activity to this day.
The launch of the Gaia satellite in December 2013 completely transformed our comprehension of the Milky Way
Collectively, these findings contribute to a fresh narrative of the tumultuous history of our Galaxy and its ongoing transformation into the future. According to Michael Pietersen, an astronomer at the University of Edinburgh, “Our perspective of the Milky Way has undergone rapid transformation. The Milky Way is now understood to be a dynamic entity, experiencing rapid changes across its entirety.”
The earliest generation of stars
In order to gain insight into the earliest stages of the Galaxy’s formation, astronomers are actively searching for stars that existed during that time period. These stars were composed primarily of hydrogen and helium, which are the most fundamental elements in the universe. Fortunately, the smallest stars from that era had a much slower rate of burning compared to their counterparts, allowing them to continue emitting light to this day.
After numerous years of careful observation, scientists have compiled a list of 42 ancient stars referred to as ultra-metal-poor stars (astronomers use the term “metal” to describe any element heavier than helium). According to the accepted history of the Milky Way, these stars should mainly be found in the halo – the initial part of the Galaxy. On the other hand, the disk – which is believed to have taken around a billion years to form and flatten – should be populated by stars containing heavier elements such as carbon or oxygen.
In late 2017, Sestito made the decision to investigate the movement of this group of metal-poor stars by creating a program that would analyze the data collected from the Gaia project. The goal was to see if the paths these stars took on the celestial sphere could provide insight into the origins of the halo.
Sestito selected 42 ancient stars from the dataset and studied their trajectories. The majority of these stars followed the expected paths within the halo. However, there was a subset – approximately 25% – that appeared to be moving in a different manner. These stars seemed to be confined to the disk plane, which is the youngest part of the Milky Way galaxy. Sestito was taken aback by this discovery and expressed his astonishment, albeit with slightly stronger language. He wondered, “What is happening here?”
Follow-up research has verified that these stars have resided within the disk for an extensive period and are not merely passing through as tourists. Utilizing two recent observations, Sestito and his colleagues have curated a collection of 5000 stars with low metal content. Among this assemblage, a small number have clearly established themselves as permanent inhabitants of the disk. Another team of scientists meticulously examined an additional 500 stars discovered during a separate observation and determined that one out of every ten possesses orbits aligned with the plane of the disk. Additionally, a third team of researchers scrutinized multiple stars with varying metallicities (and consequently varying ages) that orbit within a flat disk. “This represented a wholly novel discovery,” remarked Paola di Matteo, primary author of one of the studies and an astronomer affiliated with the Paris Observatory.
How did these anachronisms come to be? Sestito proposed that certain clusters of ancient gas somehow managed to evade all the metals expelled by supernovae for extended periods of time, after which deceptively old stars formed from this gas. Alternatively, the disk may have begun to take shape at the same time as the halo – 1 billion years ahead of schedule.
To determine which of these hypotheses is more plausible, he reached out to Tobias Buck, a researcher at the Potsdam Astrophysical Institute in Germany specializing in generating digital simulations of galaxies. Previous attempts at such simulations have typically resulted in the halo forming first and the disk forming later, as anticipated. However, these attempts had relatively low resolution.
These computerized simulations depict the formation and development of a galaxy that closely resembles our own Milky Way over a span of 13.8 billion years, spanning from the inception of the Universe to the present day. The distribution of imperceptible dark matter is presented in the left column. The middle column illustrates the temperature of the gas, with blue indicating colder regions and red highlighting hotter areas. The right column showcases the density of stars. Each row corresponds to a specific scale: the top row offers a detailed view of the galactic disk, while the middle row presents a slightly more distant perspective of the halo. The bottom row depicts a panoramic view encompassing the galaxy’s surroundings.
Buck enhanced the quality of the simulations by around 10 times. Each iteration of such a simulation demanded considerable computational capabilities. Despite having access to the Leibniz Supercomputing Center in Germany, he had to execute one simulation on a solitary computer. For one simulation at the Leibniz supercomputer center in Germany, it took approximately three months to complete. He performed this particular simulation six times in total.
Out of these six instances, he achieved a double of the Milky Way in five of them. In two of these simulations, the disk encompassed a substantial quantity of stars with low metal content.
The origin of these ancient stars in the disk is quite fascinating. In simple terms, they can be considered as stellar immigrants. Some of these stars were actually born in clouds that existed long before the formation of the Milky Way. These cloud stars eventually found themselves in orbits that would later become part of the galactic disk. On the other hand, some stars originated from dwarf galaxies that had collided with the Milky Way and ended up in the plane of the forming disk.
According to the findings published by the researchers in November 2020, it appears that the traditional models of galaxy formation were not entirely accurate. While gas clouds do collapse into spherical halos as predicted, the arrival of stars at specific angles can also trigger the formation of the disk. “The theorists weren’t entirely mistaken,” Buck commented. “They simply didn’t have the complete picture.”
The challenges did not stop there. “Gaia” played a role in revealing conclusive proof of devastating collisions. Astronomers had already hypothesized that the Milky Way harbored vibrant life, but Helmer Koppelman, a researcher at Princeton’s Institute for Advanced Study, managed to identify distinct remnants of a massive merger by analyzing the data provided by Gaia.
Koppelman remembers that Gaia’s data from April 2018 was released on a Wednesday, and the rush to download the files almost crashed the project’s website. He analyzed the data on Thursday, and by Friday he realized that he had made a significant discovery. There were countless stars moving in peculiar patterns at the heart of the Milky Way, indicating that they had come from a dwarf galaxy. Koppelman and his colleagues quickly prepared a brief scientific paper by Sunday, and a more comprehensive analysis was completed by June.
It is possible to discover debris resulting from the collision of galaxies in various locations. As much as half of the stars within the inner area of the halo, which has a diameter of 60,000 light-years (with the halo itself having a radius of hundreds of thousands of light-years), may have originated from this particular collision. This event could have contributed to a 10% increase in the total mass of the Milky Way. “This discovery is a game-changer,” stated Koppelman. “I had anticipated the presence of numerous distinct small objects.”
A simulation depicting the development and progression of a galaxy resembling the Milky Way throughout a span of 10 billion years. Many small dwarf galaxies descend into the primary galaxy’s disk and often integrate into it.
The galaxy that collided with our own was given the name Gaia-Enceladus by our team, in honor of the Greek goddess Gaia and her son Enceladus from Titan. Interestingly, another team also discovered this galaxy independently and named it “Sausage” due to its distinctive shape in certain orbital maps.
Clues of potential mergers can also be detected within globular star clusters. Diederik Kruijssen, a scientist at the University of Heidelberg in Germany, utilized simulations of galaxies to train a neural network that closely examined these clusters. By running the network, he was able to analyze the clusters’ age, composition, and orbital patterns. Using this data, the neural network successfully reconstructed the past collisions that gave rise to the galaxies. Kruijssen then applied this newfound information to actual data from the Milky Way. The program accurately recreated both well-known events, such as the collision with Gaia-Enceladus, and a more ancient and significant merger that the team of researchers named Kraken.
In August, Kruijssen’s team released a compilation of the Milky Way’s mergers with dwarf galaxies that gave rise to it. The scientists also made projections for an additional 10 previous collisions, which they expected to confirm with the help of independent observers. “We haven’t discovered those 10 collisions yet,” Kruijssen stated, “but we will.”
These mergers have led some astronomers to propose that the halo might be composed almost entirely of immigrant stars. Models from the 60s and 70s had predicted that the majority of stars in the Milky Way formed locally. However, as time progresses, an increasing number of stars are turning out to be extragalactic. According to Di Matteo, astronomers may no longer need to assume that numerous, or any, stars were born locally.
A quietly growing galaxy
The history of the Milky Way has been relatively calm recently, but newcomers continue to be drawn to it nonetheless. Astronomy enthusiasts in the southern hemisphere have the opportunity to witness a pair of dwarf galaxies, known as the Large and Small Magellanic Clouds, with the naked eye. For many years, these two galaxies have been seen as loyal companions to our own, similar to the moons of the Milky Way.
However, a series of observations conducted by the Hubble Telescope between 2006 and 2013 have revealed that they bear a closer resemblance to meteorites hurtling towards us. Nitya Kallivayalil, an astronomer from the University of Virginia, has calculated that they are actually moving directly towards us at a speed of approximately 300 km/s – nearly twice as fast as previously believed.
The view of Mount Bromo, an active volcano in Java National Park in Indonesia, is enhanced by the presence of the Great and Small Magellanic Clouds in the night sky.
After analyzing the data a few years later, Jorge Peñarrubia and his team from Edinburgh’s Royal Observatory made a surprising discovery – the high-speed clouds were much more massive than previously believed, potentially weighing 10 times more.
“We were constantly surprised by our findings,” remarked Peñarrubia.
Several research groups had predicted that these unexpectedly heavy dwarf galaxies could be exerting a gravitational force on parts of the Milky Way, and this year, Peñarrubia and Peterson joined forces to search for evidence supporting this hypothesis.
One of the challenges in studying the movement of galaxies is that the Milky Way is a vast collection of stars, making it difficult for astronomers to observe the larger picture. To overcome this, Peñarrubia and Peterson dedicated much of their time during the quarantine to finding a way to account for the movements of the Earth and Sun, as well as to average out the motion of the stellar halo. This allowed them to establish a stationary background against which they could analyze the outer boundary of the halo.
Through this calibration process, they made an interesting discovery: the Earth, Sun, and the surrounding disk are all moving in the same direction. However, they are not heading towards the current position of the Large Magellanic Cloud, but rather towards where it was one billion years ago. Pietersen explained that this is because the Galaxy is a slow-moving entity with delayed reactions. Their findings were recently published in the journal Nature Astronomy.
The motion of the disk in relation to the halo disrupts the basic assumption of equilibrium in the Milky Way. It has the ability to rotate and shift in space, but most astronomers have assumed that over billions of years, the mature disk and halo have established a stable configuration.
Peñarrubia and Petersen’s analysis disproves this assumption. Even after 14 billion years, mergers continue to shape the overall structure of the Galaxy. This represents the latest revelation in our understanding of the processes occurring in the vast milky stream suspended in our sky.
“We now require a new model to describe the future and history of the Milky Way that we believed we already understood,” stated Pietersen.
The most recent information provided by the Gaia spacecraft has caused scientists to completely reconsider the origins and development of our galaxy. As a result, they are now also considering the future of the Milky Way in a different light.
When Khoisan hunter-gatherers from sub-Saharan Africa gazed up at the meandering path of stars and dust that adorned the night sky, they perceived it as the glowing remnants of a campfire. Polynesian sailors saw it as a shark devouring clouds. And the ancient Greeks saw it as a flowing stream of milk, known as gala (γάλα), which eventually led to the modern term galaxy.
During the 20th century, scientists in the field of astronomy made a groundbreaking discovery. They found out that our Milky Way, which was previously thought to be the only river of silver in the universe, is actually just a small part of an expansive cluster of stars. This led them to create their own narrative about the origins of our galaxy. According to their findings, the Milky Way came into existence approximately 14 billion years ago when massive clouds of gas and dust were drawn together by the powerful force of gravity. As time passed, two distinct structures began to take shape: first, a colossal spherical “halo,” and then a concentrated, luminous disk. It was billions of years later that our solar system formed within this disk. Today, when we gaze up at the night sky, we can observe what appears to be “spilled milk” – a side view of that immense, radiant disk.
However, in the past couple of years, researchers have managed to rewrite almost every significant chapter of the Milky Way’s history. What caused this shift? The answer lies in the availability of superior data that has allowed for more accurate analysis.
On April 25, 2018, Gaia, the European space observatory, released an unprecedented amount of information regarding stars. It is crucial to acknowledge that Gaia’s data provides an intricate description of around 1 billion stars (as mentioned by an expert in December). Previous research had only uncovered the movement patterns of a few thousand stars. The latest data has sparked a renewed fascination with our Milky Way galaxy. “Gaia has initiated a revolutionary shift,” Federico Sestito, an astronomer at the Strasbourg Astronomical Observatory in France, elucidated to Quanta Magazine.
Astronomers were quick to access a dynamic star map created by the Gaia observatory, leading to a series of exciting discoveries: certain regions of the Milky Way were found to be older than previously believed, offering evidence of dramatic collisions that influenced the turbulent early years of our Galaxy. Additionally, signs of ongoing and unexpected changes in the Galaxy were uncovered. These findings have fundamentally transformed our understanding of the Milky Way. “Our perception of the Milky Way has undergone a rapid and significant shift,” remarked Michael Petersen, an astronomer at the University of Edinburgh.
To catch a glimpse of the earliest moments in the history of the Galaxy, astronomers have been on the lookout for stars that have been present since the very beginning of the formation of the Milky Way. These stars were made up of nothing but hydrogen and helium – the pure building blocks of the universe. Luckily, stars that are not rich in metals can survive for a very long time, which means that many of them still exist and continue to shine.
After many years of extensive research, scientists have identified a total of 42 of these ancient stars, which are referred to as ultra metal-poor stars (in the field of astronomy, any element heavier than helium is considered to be a metal). Based on the accepted history of the Milky Way, these stars should be scattered throughout the galaxy’s halo, which is the first part of the galaxy to take shape. In contrast, stars in the disk, which took around a billion years longer to form, should contain higher levels of heavy elements like carbon and oxygen.
In 2017, Sestito made the decision to examine the movement of the metal-depleted swarm by developing code to analyze the forthcoming Gaia results. His goal was to gain insight into the origin of the “halo”.
Since the publication of the Gaia catalog data, Sestito has isolated 42 ancient stars from the complete data set and monitored their motion. He discovered that the majority of these stars traversed through the outer halo. However, a portion of the stars (approximately one in four) did not. Instead, they remained in the disk, which is the youngest area of the Milky Way. Sestito was taken aback by this finding.
Further research has confirmed that these stars are permanent inhabitants of the disk, not just visitors. After analyzing the data, Sestito and his team have compiled a library of approximately 5,000 low-metal stars. Among them, several hundred are believed to be a permanent part of the Galaxy’s disk. Another study examined around 500 stars and discovered that about one in ten of them have orbits similar to the Sun’s orbit. A third group of researchers observed stars with varying metal content and ages orbiting a flat disk. According to Paola Di Matteo, an astronomer at the Paris Observatory, “This is a completely novel finding.”
What is the origin of these anachronisms? Sestito proposed that the pockets of ancient, untainted hydrogen gas might have evaded the presence of metals expelled by supernovae over the course of the galaxy’s existence and subsequently collided to give rise to stars that would appear older. Another hypothesis posits that the formation of the disk may have commenced concurrently with the halo, nearly 1 billion years prior to the initially estimated timeline.
In order to determine which version was the most likely, he reached out to Tobias Buck, a researcher at the Leibniz Institute for Astrophysics in Potsdam, Germany, who has expertise in modeling the populations of galaxies. As anticipated, Tobias’s previous attempts to unravel the enigma of our Galaxy’s appearance generally resulted in the conclusion that a halo materialized first, followed by a disk. However, these endeavors involved modeling with relatively limited spatial resolution. At the behest of Sestito, Buck enhanced the modeling precision by a factor of approximately 10.
How did these ancient, low-metallicity stars end up in the disk? To put it simply, they were star immigrants. Some of them were born in clouds prior to the formation of our Galaxy. These clouds then randomly sent some of their stars into orbits that eventually became part of the galactic disk. Other stars originated from small “dwarf” galaxies that interacted with the Galaxy and became part of the developing disk.
The findings, which the team published in November, indicate that traditional models of galaxy formation were incomplete. As anticipated, gas clouds condense into spherical halos. However, stars falling at right angles can also form a disk. “The theorists were not mistaken,” Buck explained. “They simply lacked observational data.”
The restive younger generation
The challenges do not cease there. By utilizing the Gaia observatory, astronomers have discovered conclusive proof of colossal collisions in the past. Astronomers had previously presumed that the Milky Way had a tumultuous early existence, however, Helmer Koppelman, an astronomer presently working at the Institute for Advanced Study in Princeton, utilized Gaia data to identify specific remnants from one of the largest mergers. In every direction, he observed a substantial number of halo stars oscillating within the center of the Milky Way in a peculiar manner – a hint that they originated from the same dwarf galaxy. Galactic remnants were present throughout. It is possible that approximately half of all the stars in the halo (which extends hundreds of thousands of light-years in all directions) originated from this singular collision, which might have augmented the mass of our galaxy by 10%. “This discovery completely altered my perspective,” remarked Koppelman. – “I was anticipating numerous minor collisions.”
The team decided to call the small galaxy that merged with our Galaxy Gaia-Enceladus, taking inspiration from the Greek goddess Gaia and her titan son Enceladus. Around the same time, another independent team from the University of Cambridge identified a similarly small galaxy and named it Gaia Sausage due to its distinctive shape on maps.
When the Milky Way and Gaia-Enceladus collided approximately 10 billion years ago, it is believed that the thin disk of our galaxy sustained significant damage. Astronomers are still debating the reasons behind the division of our galactic disk into two parts: a thin disk and a thicker bulge, where stars move in an oscillating motion as they orbit the center of the Galaxy. According to Di Matteo’s research, it is suggested that Gaia-Enceladus caused a major disruption, effectively inflating the disk during the collision. “The initial ancient disk formed relatively quickly, and then we believe Gaia-Enceladus essentially shattered it,” explained Koppelman.
In August, Kruijssen’s team released a potential timeline for the merger of our Galaxy (the Milky Way) and the dwarf galaxies that gave rise to it. They also proposed the existence of 10 additional previous collisions, which they anticipate will be verified by independent observations. “We haven’t discovered the other 10 yet,” Kruijssen stated, “but we certainly will.”
These conjectures have prompted some astronomers to suggest that the galaxy’s halo might be primarily comprised of immigrant stars. Models from the 1960s and 1970s indicated that the majority of stars in the Milky Way halo would have formed through non-collision processes. However, as more and more stars were identified as originating from other galaxies, these models came under scrutiny.
Does the movement have no end?
Our Milky Way galaxy has not experienced much activity in recent history, but there are concerns about new collisions with neighboring galaxies. People who observe the night sky in the Southern Hemisphere can see two small galaxies known as the Large and Small Magellanic Clouds with their naked eye. Astronomers have long believed that these galaxies are stable companions that orbit our galaxy. However, a series of observations made by the Hubble Space Telescope between 2006 and 2013 showed that they are more similar to falling meteorites. Nithya Kallivayalil, an astronomer at the University of Virginia, discovered that these hot clouds are moving upwards at a speed of about 330 kilometers per second, which is almost twice as fast as expected. When a team of scientists led by Jorge Peñarrubia, an astronomer at the Royal Observatory of Edinburgh, examined the data a few years later, they concluded that these fast-moving clouds must be much larger than previously believed, possibly ten times larger. “It was one surprise after another,” said Peñarrubia.
There has been speculation among different groups that powerful dwarfs could be responsible for dragging parts of the Milky Way with them. This year, Peñarrubia and Petersen have come together to validate these findings. The challenge in studying our Galaxy, the Milky Way, is that it is a vast collection of stars where we are just small components. In order to address this, Peñarrubia and Petersen focused on accounting for the Earth’s and Sun’s motion, as well as the motion of the halo stars, in order to establish a stationary background using the outer boundary of the halo.
By calibrating the data in this manner, the researchers discovered that the Earth, Sun, and the rest of the disk they are on are all moving in the same direction. These findings have recently been published in Nature Astronomy.
The interaction between the galactic disk and the halo challenges a fundamental assumption: that the Milky Way is a stable entity. Peñarrubia and Petersen’s analysis demonstrates that the belief in a steady Galaxy may not hold true. Even after 14 billion years since the initial Galactic merger, our own Milky Way continues to evolve. This realization represents a significant shift in our understanding of the Galactics as a dynamic system. “All of our previous notions about the future and history of the Milky Way,” remarked Petersen, “must be completely reconsidered.
Astronomy has always captivated me, and I have delved into various sources of knowledge on the subject, including books, documentaries, and articles. Today, I will discuss the origins of our galaxy, the different names it has been known by throughout history, and the various galaxies that exist in the vast Universe.
Origin and Former Names of Our Galaxy
Throughout history, our galaxy has been known by various names before becoming universally referred to as the “Milky Way”. Each nation had its own unique way of describing the distinct patterns and shapes seen in the sky:
- The Bulgarians referred to it as “The Way of Sinners”.
- The Turks named it “The Road to Mecca”.
- Many Indian tribes called it the “Heavenly River of Spirits”.
- Ancient China knew it as the “Star River”.
- In India, it was known as the Silver River.
Allow me to provide you with the available information regarding its inception. Approximately 14.5 billion years ago, a colossal spinning mass of gases, referred to as a proto-galaxy, materialized. This proto-galaxy consisted predominantly of hydrogen (80%) and helium (20%). Over the course of billions of years, it contracted due to its own gravitational pull and, upon reaching its density threshold, fragmented into numerous pieces. Consequently, this event initiated the formation of the initial stars, including the star that illuminates our own solar system – the Sun.
Galaxy Classification
The classification of galaxies is quite extensive. For convenience, three main groups are usually distinguished:
Now I will discuss each type separately.
Spiral galaxies are characterized by the presence of old stars in the central part, while new stars are located in the outer edge. The disk of spiral galaxies is composed of interstellar dust and they have a spiral shape. Our Milky Way belongs to this type of galaxy.
Elliptical galaxies, on the other hand, have a spheroid or lens-like shape and do not have spiral arms. It is believed that they are formed from the merging of spiral galaxies.
The formations that do not have a distinct structure and appear irregular in shape represent a disordered collection of stars. They are highly uncommon in the Universe, and the nearest ones to us are the Small and Large Magellanic Clouds.
During summer nights, when the darkness envelops the surroundings and the sky is devoid of clouds, I often attempt to locate the faintly visible band of light encircling the celestial sphere. It resembles a trail of milk accidentally spilled by someone’s hand. This trail is the celestial path known as the Milky Way in ancient times.
Understanding the Formation of Our Galaxy
Our galaxy, known as the Milky Way, is a vast stellar system that takes on the shape of a spiral with a dense core. Through the lens of a telescope, the Milky Way appears as a scattered collection of starry particles, while to the naked eye it presents itself as a luminous expanse in the night sky. The positioning of the Sun on the outskirts of the Galaxy grants us the opportunity to witness this phenomenon. When our line of sight aligns with the galactic plane, the distant stars blend together, creating the radiant glow that we refer to as the Milky Way.
Understanding our Galaxy
In ancient times, people held the belief that this vast expanse of stars was the celestial pathway traversed by angels as they ascended to the heavens. Our Galaxy, also known as the Milky Way, encompasses all the stars that illuminate the night sky, including our own Sun. In total, there are more than 100 billion stars within its boundaries. The Milky Way, along with three neighboring galaxies, is part of a larger assemblage known as the Local Group. This cluster consists of several dozen member galaxies, with only three being visible to the naked eye.
Interstellar Collisions
The gravitational forces between galaxies result in galactic collisions. However, the vast distances between the stars within a galaxy prevent them from annihilating each other. Currently, our galaxy is on a trajectory that poses a threat of bringing it closer to the Andromeda galaxy. This collision is projected to occur in approximately 5 billion years, leading to the formation of a new and unique galaxy. The scale of our galaxy is immense, exemplified by the fact that if I were to send a message to a creature residing in the center of our expansive galaxy, I would not receive a response until 60,000 years later! This astounding beauty also serves as inspiration for artists, who have observed that our Sun is merely a minuscule star within one of the galactic spirals.
From my earliest days, I have been captivated by the celestial expanse above. I could spend endless hours gazing upon it. During my school years, I eagerly absorbed every word my astronomy teacher spoke. The names of stars, comets, and galaxies all seemed like enchanting tales. Many of these names were bestowed by ancient scientists, and the true meaning behind them has been lost to time, leaving only myths and legends. And one such name is that of our own galaxy, “the Milky Way.” This name remains mysterious to many and has sparked countless speculations.
What is the significance of the Milky Way?
One of the most well-known myths is the story of how Zeus placed the infant Hercules at the breast of his sleeping wife, Hera, in order to make him a demigod. However, Hera woke up and pushed the baby away, causing her milk to spill and create the “milky way” in the sky. Additionally, in ancient times, it was believed that the soul would travel along this “milky way” after death to reach another world. There is also a legend that suggests this pathway was used by beings from outer space to come to Earth. In my opinion, the name “Milky Way” comes from its resemblance to a luminous white path and its connection to the Greek word “galaxy,” which means a milky celestial object.
Everything we observe in the sky, such as the sun, the stars, and our planet, is part of our Milky Way galaxy. In reality, there exist numerous galaxies, encompassing a vast number of stars, and not all of them have designated monikers.
The Characteristics of Our Galaxy
I recall from my astronomy course that our galaxy possesses a spiral shape, resembling a spiral itself, and our solar system is situated on the outer edge of this spiral. Moreover, we are in constant motion. In summary, we can assert that our galaxy comprises:
- The Milky Way galaxy has a central core that houses a black hole;
- There are spiral arms in the galaxy that contain various celestial bodies such as stars and planets. These arms are in constant motion around the central core;
- There is also a cloud of gas and clusters of stars surrounding the Milky Way, known as the “halo”.
Researchers have also proposed that our galaxy has acted as a “cannibal,” consuming other galaxies. Additionally, they speculate that this phenomenon may occur again in the future if our galaxy comes into proximity with another galaxy, unless it becomes “eaten” by itself. However, this event is projected to take place billions of years from now, so there is no immediate cause for concern.
Scientists have discovered the embryonic center from which the Milky Way originated, with an age surpassing 90% of the age of the Universe. The detailed examination of this recently found entity will provide valuable insights into the history of our celestial abode’s formation, according to Anatoly Glyantsev, a science columnist for Forbes.
A group of scientists has uncovered thousands of exceedingly ancient stars deep within the Milky Way. These stars are estimated to be over 12.5 billion years old, nearly equivalent to the age of the universe (13.8 billion years). The researchers propose that these stars represent remnants of a primordial galaxy that served as the foundation for the Milky Way’s existence.
Mergers and acquisitions
Our immense galaxy did not achieve its current form all at once. Numerous small star systems were drawn together and collided, merging into the magnificent Milky Way. By examining the paths and chemical makeup of stars, scientists strive to uncover their origins and reconstruct the history of our Galaxy. This area of study is commonly referred to as galactic archaeology.
Throughout the past 11 billion years, at least five neighboring galaxies have collided and combined with our own galaxy. However, this process began much earlier. Recently, a team of scientists from Germany, the UK, the US, and China uncovered a primordial galaxy nucleus that occupied the position of the Milky Way within the first billion years of the universe’s existence.
The astronomers utilized up-to-date data collected by the Gaia orbiting telescope. With a price tag of approximately € 1 billion, this instrument has provided us with the most comprehensive stellar catalog ever compiled, containing 1.8 billion stars. Gaia has successfully determined the coordinates, trajectory, and spectrum of a significant number of these stars, enabling us to infer their chemical composition and, subsequently, their age.
Indications of Aging
Virtually all atoms that emerged following the occurrence of the Big Bang consisted of the most basic chemical elements, hydrogen and helium. The remaining elements of the periodic table, with a few exceptions, were created through the actions of stars. Novel elements were generated within the thermonuclear furnaces of celestial bodies, in supernova explosions, and through the collisions of neutron stars. When burnt-out stars perished, they dispersed their matter throughout the cosmos. From this material, new stars were formed. The oldest stars can be identified for a simple reason – they are notably deficient in elements heavier than helium.
The origin of the celestial river
The researchers conducted a study utilizing data collected from Gaia’s archives, focusing on 1.5 million prominent stars located in the central region of the Milky Way. Among these stars, approximately 70,000 displayed a metallicity [M/H] less than -1, including 20,000 with [M/H] less than -1.5, and around 4000 with [M/H] less than -2. These specific stars are estimated to have an age exceeding 12.5 billion years.
While this figure is not a groundbreaking record, it is worth noting that the Milky Way is home to individual stars that are over 13 billion years old. However, it remains unclear whether these ancient stars originated within our galaxy or were introduced through the absorption of other galaxies.
The numerous stars identified by Gaia, however, are likely part of the ancient nucleus of the Milky Way. Several pieces of evidence support this hypothesis. Firstly, nearly all of these celestial bodies are situated within a 16,000 light-year radius from the Galaxy’s center, with the majority falling within 9,000 light-years (representing the initial 18% of the Milky Way’s total radius). Secondly, the intricate composition of these stars suggests that they formed within the heart of a massive system. It is reasonable to believe that this system is the protogalactic embryo of the Milky Way. Lastly, these stars move harmoniously in nearly circular orbits. In contrast, remnants from destroyed and assimilated extraterrestrial galaxies typically follow elongated elliptical trajectories.
The authors do not assert that the star system they uncovered was part of the initial collision that initiated the formation of the Milky Way. Reconstructing the history of the Galaxy prior to such a progenitor is exceedingly difficult. The first instances of “mergers and acquisitions” occurred too far in the past, and the participants were too small in mass to leave behind evidence of these cataclysmic events. Nevertheless, the structure identified by the authors has persisted as a cohesive entity for over 90% of the Universe’s age, and the majority of the Milky Way’s present-day mass has accumulated around it as a central core. Thus, it could be aptly referred to as the root or source of the Milky Way.
Astronomers stress that the current discovery should only mark the start of investigating this source. “Gaia” is a remarkable telescope, but it has only scratched the surface in its monumental task of surveying 1.8 billion stars. What we truly require are targeted observations of the Galactic core, which can yield valuable insights into the ancient history of our celestial abode.
A multitude of individuals hold aspirations of exploring the great unknown. However, this boundary exists not just on our planet but also in the vastness of space. Where exactly does this demarcation lie, distinguishing our habitat from the uncharted territory beyond? The answer lies within the realm of space exploration. After all, not everyone possesses knowledge regarding the specific galaxy that houses planet Earth.
The appearance of our star cluster
Ever since we were young, gazing up at the night sky and observing the mesmerizing constellation of stars, we have always pondered over the true form and structure of the Milky Way in the vast expanse of outer space.
As per the study of celestial objects, our incredible star cluster belongs to the spiral category. In the cosmos, there are approximately 55% of all star formations that fall into this classification. They resemble a spiral dish with sleeves.
At the heart of our galaxy lies a keystone that will vanish as resources are depleted. Additionally, astronomers have identified a massive black hole and a slightly smaller one in the central region of the Milky Way.
There is a stellar halo encircling the disk.
Astronomers propose that a vast quantity of dark matter exists in the unilluminated region of the corona.
The concentration of stars is higher near the center compared to the outskirts.
When gazing up at the night sky, the only visible portion of the Milky Way is a strip of stars. This is due to the fact that our solar system is located within the galactic disk. In other words, humanity can only witness a fraction of the vast expanse of stars that make up our galaxy.
It should be noted that our world is merely a component of cosmic expanse.
The main characteristics of our galaxy
A lot of individuals in school were intrigued by the moniker of our star cluster. The origin of the name of this galactic system has attracted their attention.
The genesis of our galaxy’s name can be traced back to an ancient Greek myth involving the notorious Chronos, known for his insatiable appetite for devouring his own offspring. Faced with desperation, Rhea, the mother of Zeus, devised a clever plan to save her final child. She cunningly presented the titan with a package containing a stone, fooling him into thinking it was Zeus.
Chronos clasped it within his grasp and returned it to the mother for nourishing the infant. Rhea’s lactation descended upon the stone and transfigured into the celestial phenomenon known as the Milky Way. In due course, Zeus overcame his progenitor and ascended as the supreme deity of Olympus, joined by his divine brethren and siblings.
The gravitationally bound system has the capacity to assimilate smaller siblings as well. Over time, the larger neighboring galaxy Andromeda will likewise undertake the same process with the Milky Way.
The process of absorption is currently taking place in the Sagittarius dwarf star system.
In the coming years, a similar destiny awaits our satellites – the Large Magellanic Cloud and the Small Magellanic Cloud.
Our galaxy is already in the process of breaking down their structure, transforming them into clouds consisting of celestial bodies and gases.
Here is a visual representation of the formation of our galaxy:
Characteristics and Parameters of the Milky Way
Astronomers and astrophysicists have conducted numerous observations and calculations to determine the size of our galaxy, the Milky Way. These measurements have been carried out using modern telescopes, resulting in periodic adjustments to the estimated size.
Based on the most recent data, the composition of the Milky Way galaxy is characterized by the following attributes:
- The thickness of the galaxy is estimated to be around 1000 light years in the disk section, and about 3000 light years in the spheroidal compression of stars near the center.
- The diameter of the disk is estimated to be up to 200 thousand light years.
The mass of the celestial body originates from the enigmatic dark matter in the surrounding halo. Thus, the estimated mass of our domain amounts to 1.5×1011 solar masses.
Discovered by Japanese researchers, a supermassive dark matter weighing 4.3 billion solar masses resides in the center of our galaxy. Additionally, there is a black hole located 190 sv years away from the core of our star cluster, measuring 100,000 solar masses.
Exploring the Composition and Structure of the Milky Way
A group of researchers has delved into the intricacies of our galactic abode.
The following elements were disclosed:
The Sagittarius Pleiad hosts the galactic core, which emits a frigid radiance reaching temperatures of up to 10 million degrees Celsius. Positioned at the forefront is a conglomerate of ancient, obsolete celestial bodies journeying in an elongated trajectory.
The core of our galaxy contains a region with an incredibly strong gravitational force, capable of pulling in even light. Revolving around this massive black hole is a slightly smaller companion.
It’s a fascinating fact that the luminaries are arranged more densely around the nucleus than towards the outer edge. Additionally, celestial bodies in close proximity are more influenced by the gravitational pull of black holes, resulting in unique trajectories within the Universe.
Scientists have recently discovered a cluster of ancient red stars at the center of the Milky Way galaxy.
These stars are surrounded by a ring of gas that contains molecular hydrogen.
This unique region of the galaxy has been observed to have the highest rate of star formation, which may be attributed to the interaction of gas in the creation of new stars.
Our galaxy’s disk is comprised of various elements, including constellations, as well as nebulae made up of dust and gas.
The disk is adorned with spiral arms, each adorned with a unique name, that extend in various directions.
The Milky Way, our galaxy, formed on the outer edge of the Orion arm. The vast sphere of stars that make up our galactic community stretches out 8 light-years into space. This stunning halo is also known as the Corona.
The Galaxy consists of various celestial bodies:
- ancient stars that are not very massive anymore;
- small astronomical objects;
- clusters of stars;
- heated gas.
The celestial objects within the Corona exhibit a gradual movement in an elongated circular path. Simultaneously, numerous entities travel at varying velocities and along diverse trajectories.
Based on a particular hypothesis about the genesis of the galaxy, our star cluster was separated from small formations surrounding the cosmic object approximately 12 billion cosmic years ago. These formations have now become a cluster of dying stars.
Dimensions
The size of the system is determined by the number of the largest stars and nitrogen-containing dust particles within it.
Each star in our galaxy has its own orbiting bodies – planets. Scientists have estimated that there are between 10 to 99 billion planetary systems in our galaxy based on their calculations.
When it comes to posing a challenging query, such as determining the number of planets in the galaxy, it is important to acknowledge that the answer will only be an approximation. At present, specialists have estimated the count to range from 800 billion to 3,200 billion.
The total count of stars in our galactic abode
When gazing at the nocturnal heavens, astronomers are perpetually intrigued by the sheer number of celestial bodies encompassed within our gravitationally linked domain.
Currently, the worth has been determined to be 400 billion. Positioned at the core, there exists a nebula that serves as the birthplace for youthful celestial entities.
The system is surrounded by a spherical halo that encompasses the stars of the Milky Way, whose formation is reaching its completion. These celestial entities boast an age of up to 14 billion years, coinciding with the age of our galaxy. The Commonwealth of Luminaries comprises approximately 100 billion diminutive structures.
The energy distribution in the Cosmos:
Brightness
When observing the night sky from Earth’s surface, one cannot help but be amazed by the luminous strip that spans across the expanse of space, known as the Milky Way.
The Milky Way galaxy is a luminous society of stars. The galaxy’s emission relies on the brightness of its individual components.
Their emission consists of light in two distinct bands:
An astronomical entity consists of up to 230 immense celestial objects. As per classification, Wolf-Rayet stars are the most massive and brightest celestial bodies, possessing a surface temperature exceeding 50 thousand degrees Celsius, a mass approximately equivalent to 10 solar masses, and a radius ranging from 10 to 15 solar radii.
Thus, in the NGS 3603 region, a star with a mass of 116 solar masses has been identified, making it the largest star in the galaxy.
Additionally, the illumination is formed in the foundation of the celestial dwelling through obscure particles of ebony substance. This occurrence has been referred to as the surplus of the cosmic foundation.
The Position in the Cosmos
Our planet is a constituent of the solar system and is located within the Orion arm.
The core is located 2800 light years away from the planetary system. Throughout its existence, our sun has completed no more than 30 orbits, with each orbit taking 200 million light years to complete.
Discover our galaxy within the Local Group, which is part of the Virgo Supercluster. This vast region also encompasses two major and forty smaller communities of celestial bodies. Andromeda and Triangle are the Milky Way’s closest companions.
Furthermore, as per recent findings from scientists, our galaxy was formed on the fringes of the colossal super-cluster Panicle. This super-cluster, known as “vast heavens” in Hawaiian, serves as our cosmic abode.
The immense cluster spans over 520 light-years across. The gravitational pull of the gathering influences the formation of surrounding structures. Every stellar system is drawn towards its center, commonly referred to as the “great attractor.”
Simultaneously, Laniakea is a component of the elemental cluster of the Pisces-Keith Universe super-systems.
The dimensions of this cluster measure 1 billion light-years in length and 150 million light-years in width.
In 1987, an astronomer from the University of Hawaii Astronomy first discovered this galactic filament.
The Formation of Our Galaxy
In order to comprehend the mechanisms by which our galaxy, the Milky Way, came into existence, it is imperative to unravel the fundamental principles governing its formation and evolution.
As per the given explanation, the composition of our galaxy includes:
Every single object within a star cluster demonstrates movement in relation to the central point of gravity. A portion of the disk system rotates at a quicker pace, while the halo exhibits a subtle motion.
Our galaxy is orbited by clusters of stars, and the Milky Way can contain as many as a million stars.
In addition, there are hazy areas of faraway galaxies surrounding our group of stars.
An adjacent celestial object is the Andromeda Nebula.
The galaxy formed through the gravitational binding of smaller systems, which contain millions of stars. The southern part of the planet provides examples of these smaller star systems.
The Large and Small Magellanic Clouds are the names given to these galaxies. Because of the universe’s expansion, all objects are moving apart from one another, though this does not rule out the possibility of their crossing paths.
Exploring the origins and destiny of our galaxy
Understanding the universe’s vast collection of stars has intrigued humanity since ancient times. Various civilizations, as they observed the night sky, bestowed different names upon the luminous, milky band that traverses the heavens.
The name given to our galaxy is the Milky Way, which originated from the ancient Greeks. It is also commonly known as the Silver River in Chinese culture, while the Arabs refer to it as the Straw Road.
Throughout history, inquisitive individuals have attempted to quantify the luminous celestial objects, including the number of stars within the Milky Way galaxy. It wasn’t until the 20th century that astronomers extensively investigated the nature of the Milky Way and formulated a hypothesis regarding the galaxy’s genesis.
The formation stages were highlighted in the following manner:
- Approximately 14 billion years ago, due to the force of gravity, particles of dust and gas merged together;
- A few billion years later, two components emerged: initially a halo composed of the first stars, followed by a dense luminous disk;
- After billions of years, the solar system materialized on the outskirts of one of the spiral arms.
In the year 2018, new information regarding our celestial abode was released by astronomers at the European Observatory. Additionally, a dynamic celestial chart was made available, aiding in the uncovering of numerous revelations pertaining to the genesis of the Milky Way galaxy.
In the examination of celestial paths and their chemical examination, researchers have discovered numerous remnants that emerged in outer space when the Milky Way assimilated various dwarf systems. Furthermore, it has been determined that clusters of celestial objects within the Corona of our astronomical entity are part of a previously assimilated larger gravitationally-bound system.
There is a hypothesis suggesting that a star cluster had a collision with the celestial objects under discussion about 10 billion years ago. At that point in time, the proportion between our galaxy and the incoming fleet of celestial bodies was 4:1, with our part of the Universe being only four times bigger.
It was given the name Gaia-Enceland by astronomers. Following the collision, our cluster of stars experienced a series of transformations: the shape of the disk became more flat, and a new inner layer of the Corona was formed.
Scientists also acknowledge the truth that in approximately 4 billion years, our galaxy will intersect with its bigger counterpart, Andromeda. During their observations of the celestial sky, astronomers have observed the convergence of various galaxies.
In 1789, it was discovered that astronomical objects in the constellation Raven were being absorbed. Currently, one can witness the formation of new stars in that area. This is because the collision of systems disrupted the stellar gas.
The biggest members of our cluster are separated by a distance of 2.5 million light years, however, they are connected by the force of gravity. Andromeda is larger in size by nearly two times, but its mass is smaller due to its more ancient existence. As per the theory of galactic convergence, in 3 billion light years, the star clusters will draw closer to one another, and within 2 billion years, they will merge to form a new super system.
When it comes to the precision of the affiliation of stellar civilizations, contemporary science is still unable to ensure that the stellar clusters will merge and not scatter across the cosmos. However, it should be noted that Andromeda has been observed to be moving towards us at a velocity of 120 kilometers per second.
The amalgamation of significant gravitational-stellar conglomerates will likely take place at a leisurely pace, potentially resulting in no discernible ramifications for our celestial neighborhood.
Astrophysical researchers predict potential outcomes:
- the expulsion of our solar system from the newly formed structure;
- transforming into a nomadic element between galaxies.
The state of the Earth during that era will be determined by the evolution of the Sun. If the collision occurs no later than 4 billion light years from now, our planet will serve as a shield for humanity against cosmic radiation. However, as time passes, the Sun will transform into a red giant, obliterating the neighboring planets and eventually dying out. At that point, civilization will be forced to find refuge on other planets located at the outer edges of the solar system.
Fascinating footage on the formation of our galaxy
To gain a deeper understanding of the galaxy that our civilization inhabits, it is essential to view a captivating video detailing the origins and evolution of the Milky Way.
