Just like the Earth revolves around the Sun, the Solar System revolves around the center of the Milky Way. Despite moving through space at a speed of approximately 828,000 kilometers per hour, our solar system completes a complete revolution around the center of the galaxy after 250 million years. The last time our planet was in this position, dinosaurs appeared and mammals had not yet evolved.

If the center of the Milky Way is a city, we live on its outskirts. Based on this analogy, our solar system is approximately 25,000 to 30,000 lightyears away from the center of the city. Life in the suburbs is pleasant; We live in one of the smaller neighbors of the Orion-Cygnus arm, which is between the larger Perseus and Carina-Sagittarius arms. If we move towards the center of the city, we can find the arms of the Scutum-Centaurus and the arm of Norma.

On a clear night without light pollution, you can see the bright lights of the Milky Way city in the night sky. This milky white spectrum of stars, gas, and dust is a window into the universe around us.

At the heart of the Milky Way is a supermassive black hole called Arc E*. With a mass of over 4 million suns, this black hole sweeps up everything in its vicinity and feeds greedily on the vast source of stellar material around it. In 2022, an image of this black hole was published for the first time.

According to the American Museum of Natural History (AMNH), the name of the Milky Way is derived from its milky white appearance as it stretches across the night sky. In Greek mythology, this milky band appeared because the goddess Hera spread milk across the night sky.

Around the world, the Milky Way is known by different names. For example, in China it is called “Silver River” and in the Kalahari Desert of South Africa it is called “Night Spine”.

The Milky Way has always been difficult to study. Astronomers sometimes compare trying to study the Milky Way to trying to describe the dimensions and structure of a forest while standing among the trees in the forest. From our position on earth, we definitely cannot have complete nobility of the Milky Way; But two space telescopes launched since the 1990s marked the golden age of Milky Way research with their data. Major steps were taken in particular with the launch of the Gaia spacecraft from the European Space Agency in 2013.

Telescopes allowed astronomers to discern the early form and structure of some of the nearest galaxies, But reconstructing the shape and structure of our home galaxy has been a difficult and slow task. This process involves making catalogs of stars, tracking their position in the night sky, and estimating their distance from Earth.

Dutch astronomer Jan Evert, who is sometimes referred to as the Master of the Galactic System, was the first person to notice that the Milky Way was not stationary, but rotating, and estimated the speed of various stars around the center of the Milky Way. The name of the Oort cloud, a region containing trillions of comets far from the Sun, is derived from this astronomer.

Gradually, a complex vision of a seemingly ordinary spiral galaxy emerged. At the center of the Milky Way, there is a supermassive black hole, the Arc E*, with a mass of more than four million suns. This black hole was discovered in 1974 and can be observed with radio telescopes near the constellation Sagittarius.

Everything in the Milky Way revolves in a passage that ends in nothing. Around this point of nothing (black hole), there is a dense region of gas, dust, and stars known as the galactic bulge. About the Milky Way, this bump is shaped like a peanut and its diameter reaches 10,000 light years. This bulge hosts 10 billion stars out of 200 billion stars in the entire galaxy. Most of the stars in this sector are old red giants that were formed in the early stages of the galaxy’s evolution.

On the other side of the bulge, there is a galactic disc whose diameter reaches 100,000 light-years and its thickness reaches 1,000 light-years and hosts most of the stars of the galaxy, including the Sun. The stars in the disk are scattered among clouds of gas and stellar dust. When you look at the sky at night, you can see the view of the edge of this disk towards the center of the galaxy, which is very impressive.

The stars in the disc rotate around the galactic center, forming swirling streams that appear to extend like arms from the galactic bulge. The research on the formation mechanisms of rotating arms still has a long way to go, but the latest studies show that these arms were formed in a short period of 100 million years (of the 13 billion years of the galaxy).

Inside the arms, stars, gas, and dust are compacted in the regions of the galactic disk, and this increase in density leads to the formation of more stars. As a result, the stars inside the galactic disk are younger than the stars in the bulge.

Spiral arms resemble highways of gas and stars that move slowly through the arms. As material passes through the spiral’s dense arms, it compresses and forms more stars. The Milky Way currently has four spiral arms. The two main arms are Bersavush and Kaman-Shahtakhteh, and the local arms and the bow are two smaller arms. Scientists are investigating the exact position and shape of these arms with data from the Gaia spacecraft.

The Milky Way disc is not flat, but curved. This disc moves like a sliding roller while rotating. This slip, especially the massive wobble around the galactic center, is slightly slower than the stars in the disc, taking 600 to 700 million years to complete a full rotation. According to astronomers, this fluctuation could be the result of the collision of the Milky Way with another galaxy in the past.

Globular clusters are located around the galactic disk and bulge, which form a collection of ancient stars, as well as 50 dwarf galaxies that orbit or have collided with the Milky Way. All of these are surrounded by a spherical halo of gas and dust that is twice the size of the disk. According to astronomers, the entire Milky Way galaxy is located in a larger halo of dark matter. Since dark matter does not emit any light, its existence can only be detected by its gravitational effects on the motion of the galaxy’s stars. According to calculations, dark matter makes up 90% of the mass of the Milky Way.

The mass of the Milky Way galaxy with dark matter is equal to 1.5 trillion solar masses. The visible matter inside the galaxy is distributed among 200 billion stars, their planets, and clouds of gas and dust in interstellar space. Astronomers are still not sure how many planets there are in the Milky Way, but considering the discovery of several thousand exoplanets in recent years, we can estimate that there are more than 100 billion planets in the Milky Way. The number of star systems is still a mystery.

The Sun is 26,000 light-years away from the Arc E* black hole at the center of the Milky Way. With a speed of 828 thousand kilometers per hour, our star completes its orbit around the galaxy after approximately 230 million years.

The Sun is located near the edge of the local arm of the Milky Way, which is one of the two small arms of the galaxy. In 2019, using data from the Gaia mission, astronomers discovered that the Sun is moving on a wave of interstellar gas 9,000 light-years long, 400 light-years wide, and oscillating 500 light-years high above and below the galactic disk. The planets of the solar system do not rotate in the plane of the galaxy but have an inclination of 63 degrees. It’s like we’re moving sideways in the galaxy.

The black hole at the center of the Milky Way is called Arc E*. This black hole is often silent and this characteristic makes it difficult to observe. According to the 2008 findings of Reinhard Genzel and Andrea Gass, Arc E* has a mass of approximately 4.3 million Suns. The approximate diameter of this black hole reaches 23.5 million kilometers.

The huge gas disk around the E* arc has extended to a distance of 5-30 light years from the supermassive black hole. This disk is very massive and thin, and its gaseous part provides the necessary materials for the activity of the E-bow. This region also emits X-rays due to the gas feeding of the black hole, as its temperature rises up to 10 million degrees Celsius due to friction within the disk.

Scientists are looking for more information about the supermassive black hole of the Milky Way to understand how it formed and the conditions of its growth. There are two scenarios for the formation of this black hole: in the first scenario, smaller black holes grew and grew bigger by feeding on the gas and dust around them. In the second scenario, several smaller black holes have merged together to form a giant black hole.

In general, scientists are improving models for stellar black holes and intermediate black holes. These objects are formed when giant stars with several times the mass of the Sun collapse after their nuclear fusion stops. Since these stars cannot stop their gravitational collapse, they become a gravitationally powerful mass that can bend time and space around them, so that even light cannot escape.

We gradually learn about the E* arc through images like the first image of a black hole. This image shows the faint halo of hot material surrounding the black hole and its shadow. This image was captured thanks to a huge collection of observatories around the world that formed the Earth-sized telescope called Event Horizon (EHT).

Scientists are continuously collecting data from the Milky Way. However, in the early 20th century, astronomers believed that all the stars in the sky belonged to our galaxy. In the “Great Debate” of 1920, astronomers such as Herbert Curtis and Harlow Shipley discussed the scale of the universe and the prospect of “island worlds” (galaxies).

On one side of the debate, Shipley believed that the Milky Way is much larger than previously estimated and that we are not at the center of it. He also claimed that “spiral nebulae” like Andromeda were part of the Milky Way. On the other side of the argument, Curtis disagreed with Shipley’s claim about the much larger size of the Milky Way, but believed that large island worlds (galaxies) like Andromeda lay outside the Milky Way.

In the following years, astronomers tried to determine the type of our galaxy. According to the best estimates, the Milky Way is a barred spiral galaxy with a bar-like structure running through the center. Astronomers can determine the shape of the Milky Way by looking at the population of its stars as well as their movement across the sky.

We know that the Milky Way is located in the local group of galaxies, which includes more than 30 galaxies, including Andromeda, the Triangular Galaxy, and the Leo I galaxy. It is important to understand the nature of our neighbors because they may be closer than we think. The Milky Way moves towards Andromeda at a speed of more than 400 thousand kilometers per hour. No need to worry though, as our galaxy still has another four billion years to hit Andromeda.

For decades, NASA and other space agencies have been trying to observe distant galaxies in order to see what will happen when Andromeda and the Milky Way collide. In short, there is nothing to worry about, but the interesting thing is that these galaxies evolve after the merger.

For example, in 2022, scientists observed a three-way galactic collision with the Hubble Space Telescope and came to some interesting views about it. The largest galaxy of this group was in a coherent orbit with two other galaxies and due to very high gravity, it absorbed part of their material. This process led to the creation of streams of gas, dust, and other materials that flowed through the larger galaxy and could even be seen from Earth.

Although the Milky Way’s arms will certainly be lost in the process, the stars will be safe because the space between them is so vast. In other words, don’t look for stellar collisions in galactic mergers, because they won’t happen in practice. However, due to the influx of large amounts of material into our galaxy, the birth of stars and the luminosity of our galaxy will increase, and this population increase will continue for years after the collision.

So our solar system might survive because of the low risk of a stellar collision, but we would find ourselves on a different path around the galactic center. One effect of the collision will be to change the constellations we see from Earth, as the stars’ orbits shift and new stars are added to the mix.

The evolution of the Milky Way began when clouds of gas and dust began to collapse due to gravity. The first stars were born from these clouds and today we see them in clusters all over the world. The oval halo was also formed at a short distance following the flat galactic disk. Our galaxy was small in the beginning and grew with the inexorable force of gravity.

Using star position data, astronomers can determine the speed and direction of star movement in space. Because everything in space follows paths, astronomers can reconstruct the paths of stars from billions of years ago. Combining these reconstructed trajectories into a stellar movie can reveal the evolution of galaxies over several epochs.

Evidence suggests that the Milky Way has collided with smaller galaxies during its evolution. In 2018, a group of Dutch astronomers discovered a group of 30,000 stars that were moving in sync and in the opposite direction to the stars in the dataset. This motion pattern was consistent with what scientists had seen in computer simulations of galactic collisions. These stars were different in terms of color and brightness, and this showed that they came from another galaxy.

The remnants of another, younger collision were spotted a year later. The Milky Way has been swallowing up smaller galaxies until today. A galaxy called the Sagittarius (not to be confused with a black hole) orbits close to the Milky Way and has collided with the Milky Way’s disk several times over the past seven billion years. Using data from Gaia, scientists found that these collisions led to periods of intense star formation in the Milky Way, affecting its spiral shape. The research also suggests that our Sun was born during one of these collisions around 4.6 billion years ago.

To photograph the Milky Way we need a dark night sky. As a result, we have to go to places free of light pollution, and photography equipment is needed to record the little light in the sky. Fortunately, the Milky Way is visible in both the northern and southern hemispheres and can be photographed using amateur photography equipment. For this, you need equipment such as a tripod, different types of focus, and different lenses.

The Gaia spacecraft has made three updates to the stellar mass catalog since the beginning of its mission. Astronomers around the world continue to analyze the data in search of new patterns. Data from Gaia currently account for more research papers than the famous Hubble telescope. Gaia will continue its mission to survey stars until at least 2025, and its catalog could occupy astronomers for several decades.

Before Gaia, the largest data set on the positions and distances of stars in the Milky Way came from the Hipparchus mission, named after the ancient Greek astronomer. This astronomer mapped the night sky 150 years before Christ. The Hipparchus spacecraft observed almost 100,000 of the brightest stars near the Sun, while Gaia’s tally is a billion stars.

Although Gaia has observed less than 1 percent of the stars in the galaxy, astronomers can expand on their findings and simulate the behavior of the entire Milky Way galaxy.

• Nearly 90% of the Milky Way is made up of dark matter. Dark matter is invisible, yet its presence can be felt through its gravitational effects on galaxies.
• In the past, astronomers believed that all the stars in the universe were located in the Milky Way. Following the great debate, Edwin Hubble’s observations proved that the Milky Way is just one of billions of galaxies in the universe.
• The oldest star in the Milky Way is called HD 140283. This star, also known as Methuselah, is at least 13.6 billion years old.
• The Milky Way moves in space at a speed of approximately 600 km/s. Finally, our galaxy will collide with the Andromeda galaxy in about 4 billion years.
• If the Milky Way is reduced to less than 100 meters in diameter, the diameter of the solar system will be less than one millimeter.
• Nearly 17 billion exoplanets in the Milky Way are in the life belt of their planetary systems. Our galaxy must have between 100 and 200 billion planets, But the actual number is probably much higher than this estimate.
• Around the galactic disc are spherical halos of old stars and globular clusters. Nearly 90% of other stars are located within 100,000 light years from the center of the galaxy.
• The Milky Way and Andromeda are from the local group of galaxies. These two galaxies are the largest members of this group. 30 other galaxies are in this group.
• The supermassive black hole at the center of the Milky Way is called E*. The mass of this black hole reaches 4 million solar masses.

The Milky Way galaxy is the home of the solar system and the Earth. The Milky Way is named after the bright band that appears across the night sky. Our galaxy is home to more than 200 billion stars and is more than 100,000 light-years across.

Arc E* is the supermassive black hole at the center of the Milky Way with 4 million solar masses. The Milky Way has absorbed smaller galaxies in the past and has reached its current spiral bar shape. Our galaxy will merge with the Andromeda galaxy in the next 4 billion years.