Galaxies are a celestial system composed of many stars and interstellar dust, which are almost innumerable in the universe, in fact, in the early days, people did not know that there were so many galaxies in the universe where we lived, and they always thought that the Milky Way was the whole universe.
Until later, an astronomer from the United States, Edwin Hubble, when observing the distant Andromeda Nebula, found through the Cepheid variable stars in it that the Andromeda Nebula is actually very far away from us, and its diameter is even larger than the diameter of the Milky Way, so it was confirmed that the Andromeda Nebula is actually a separate galaxy system. That's when we realized that there were other galaxies outside the Milky Way.
Now, with the continuous progress of astronomical observations, we know that the Milky Way is a galaxy with a diameter of about 120,000-160,000 light-years, of which the number of stars is about 200 billion or more, although in our cognition it has become unimaginable to human beings, but the Milky Way is actually just an insignificant galaxy in the universe.
According to an extreme deep-field image taken by hubble released by NASA on September 25, 2012, scientists speculate that there are at least 1 trillion galaxies in our universe and possibly 2 trillion at most. At the same time, their size differences are also different.
For example, the Andromeda Galaxy, the closest large galaxy to Earth, has a diameter of more than 220,000 light-years, at least 1.5 times that of the Milky Way, and has 1 trillion stars. So do you know how small the smallest galaxies known to be found in the entire universe and how big the largest galaxies are?
The smallest known galaxy to be discovered is a dwarf ellipsoidal galaxy near the Milky Way, which is also a satellite galaxy of the Milky Way, which is about 112,000 light-years away from us and is called Segerry 2.
Segret 2 is incredibly small compared to most other galaxies, with the entire galaxy having a mass of only 550,000 times the mass of our Sun! The number of stars is only about 1,000, even less than the stars of the globular cluster, and its diameter is only a short 220 light-years. If we compare Segari 2 to the largest known galaxy, it's like a speck of dust.
The largest known galaxy is located in the Abell Galaxy Group, which is located 1.05 billion light-years away, discovered by the British astronomer William Herschel in 1790, and later included in the indexed star table by Emile Dreher, becoming the 1101st celestial body, so this galaxy was named ic-1101.
Ic-1101 is a giant elliptical galaxy with a diameter of at least 4 million light-years, equivalent to 25 times that of the Milky Way. If we put the Milky Way into it, it means it will take thousands of galaxies to fill it! The leftmost highlight in the image below is the Milky Way!
And ic-1101 is not only unusually large, the number of stars is also extremely amazing, it is estimated that the number of stars inside at least more than 100 trillion, compared to the 200 billion in our galaxy, it is simply pitiful!
So many people may wonder why the IC-1101 galaxy is so huge?
According to astronomers' observations and research, the reason why IC 1101 is so huge may be formed by the merger of many galaxies, because it is formed in the dense center of the galaxy group, so under the action of gravity, it constantly collides and merges with the surrounding galaxies, and finally grows step by step, becoming what we see today.