Can a galaxy grow larger by swallowing another galaxy like a black hole?

This article is based on answering similar questions from netizens. In fact, all large galaxies grow from small to large in the long-term evolution of the universe, but my understanding is that the growth of galaxies is completely different from the swallowing of celestial bodies by black holes. They are formed by the continuous collision and fusion of galaxies, which cannot be called swallowing.

Let’s talk about the present situation of the Milky Way first.

The Milky Way is the home of our solar system. The sun is just an ordinary yellow dwarf star in the Milky Way, a small or medium-sized star among the 100 to 400 billion stars in the Milky Way. The Milky Way is a flat spiral galaxy that looks a bit like a pinwheel or a discus. Because there is a huge light column in the core, with two huge main spiral wings at both ends, it is also called a barred spiral galaxy.

Previous observations suggested that the disk of the Milky Way is about 100,000 light years in diameter; new observations now suggest that the disk is likely to be 200,000 light years in diameter. This disk is made up of stars, dust, and gas, with a core thickness of only about 10,000 light years, and becomes thinner towards the edge, with an average thickness of about 2,000 light years.

In the past, it was estimated that the mass of the Milky Way is about 200 billion solar masses. Now, including dark matter, it is estimated to be about 3 trillion solar masses, of which dark matter accounts for about 83% to 85%, which means that the visible matter such as stars and interstellar dust accounts for about 450 billion to 510 billion solar masses.

The Milky Way is not a very large galaxy in the universe. The largest galaxy discovered in the universe is IC1101, which is about 1 billion light-years away from us. This is an elliptical galaxy with a diameter of about 6 million light-years. It can accommodate thousands of Milky Ways and has more than 100 trillion stars.

The direct leader of the Milky Way is the superstructure of the celestial body - the Local Group, which is composed of about 50 galaxies of different sizes. In this group, the Milky Way ranks second, second only to the Andromeda Galaxy, the largest galaxy. The remaining galaxies are smaller than the Milky Way, and most of them are dwarf galaxies. These dwarf galaxies are subject to the gravitational constraints of the largest and second largest galaxies and move around them respectively. There are two companion galaxies around the Milky Way, namely the Large Magellanic Cloud and the Small Magellanic Cloud, and more than a dozen satellite dwarf galaxies.

Our home solar system is located on an arm of the Milky Way called Orion, about 26,400 light-years away from the galactic center. The sun, along with eight planets and other small celestial bodies, revolves around the galactic center at an orbital speed of about 217 kilometers per second, completing one circle in about 225 to 250 million years.

Let’s talk about the past and future of the Milky Way.

The Milky Way is 13.6 billion years old, which means it was born not long after the universe was born. Like all galaxies, the Milky Way was much smaller than it is now when it was born. Research suggests that in the past 12 billion years of history, the Milky Way has experienced at least 12 collisions and mergers with different galaxies to become what it is today.

Astronomers study globular clusters to understand how many major collisions have occurred in the Milky Way so far. Because globular clusters are living fossils left over from the early universe, their chemical composition can be used to determine their origins, based on the rule that stars are born at the same time from the same gas. By reconstructing the orbital motion and current shape of globular clusters, it is possible to determine where these clusters came from and how many stars their predecessor galaxies had.

Based on data from the Gaia Space Telescope and the Sloan Digital Sky Survey, scientists have concluded that about 10 billion to 8 billion years ago, a dwarf galaxy called the Gaia Sausage collided with the Milky Way and then merged into the Milky Way, adding at least eight globular clusters, about 50 billion times the mass of the sun, stars, gas, dust and dark matter to the Milky Way.

According to data simulation results, the biggest collision that really changed the Milky Way came from the more distant Kraken galaxy. This collision occurred 11 billion years ago, when the Milky Way was four times smaller than it is now. The incorporation of Kraken added at least 13 globular clusters to the Milky Way.

There are now at least 150 globular clusters in the Milky Way, which are living witnesses of the many collision and merger events that have occurred in the history of the Milky Way.

The merger of galaxies has not stopped yet. At present, the Andromeda Galaxy, the largest galaxy in the Local Group, is rushing towards us (or we can say that we are rushing towards it) at a speed of about 300 kilometers per second. Scientists predict that in the next 3 to 4 billion years, these two large galaxies will collide with each other and merge into a larger elliptical galaxy.

Of course, if the skin is gone, where will the hair be attached? The satellite dwarf galaxies around the two large galaxies will also merge in, that is, the entire Local Group will merge into a large elliptical galaxy. Generally speaking, elliptical galaxies are giants among galaxies in the universe.

If humans are fortunate enough to survive until that day, they may be able to appreciate the magnificent sight of their own huge home.

In the universe, galaxy mergers continue every day

Human observation of the universe has made great progress in the past 30 years, mainly due to the advent of some of the most advanced telescopes such as the Hubble Space Telescope and the Webb Space Telescope. People's vision has extended from the light-year scale of the solar system to 200,000 light-years of the Milky Way, and then to 10 million light-years of the Local Group and 110 million light-years of the Local Supercluster.

The Laniakea Supercluster complex is 520 million light-years away, the Sloan Great Wall structure is 1.37 billion light-years away, the Hercules-Colorado Boreas Wall is over 10 billion light-years away, and so on.

The Hubble Telescope has taken several stunning photos, and the Hubble Extreme Deep Field (XDF) is the most stunning. This photo was taken in a sky area with less than one percent of the field of view of the full moon, and thousands of galaxies were captured through long exposure. The successor Webb Telescope is 100 times more powerful than its predecessor Hubble, and the images obtained by using the infrared field of view are clearer and deeper. In the same sky area of ​​the Hubble Extreme Deep Field, more and clearer galaxies can be seen.

From this, we can conclude that in the observable universe, there are conservatively estimated to be trillions of galaxies, and there may even be more than 10 trillion. Therefore, in the context of the vast universe, the tiny Milky Way is just a small grain of sand, and the sun is not even a speck of dust, let alone the Earth and the humans on it.

In the field of view of these telescopes, people have observed a variety of colorful and diverse galaxies, but they can be roughly divided into three categories, namely elliptical galaxies, spiral galaxies, and irregular galaxies. Various galaxies are variations of these major categories of galaxies.

Among these galaxies, many were found to be in the process of colliding and merging, such as the NGC4676 galaxy discovered by Hubble in the constellation Coma Berenices, commonly known as the Mouse Galaxy, which looks like two mice playing; there is also the Rose Galaxy in the Andromeda constellation 300 million light-years away from Earth, and the NGC3447 galaxy in the Leo constellation 60 million light-years away from us, all of which are galaxies in the collision and merging stage.

The Webb telescope, which was put into service not long ago, has already made many groundbreaking discoveries. It has pushed the galaxies that the Hubble telescope could see 13.4 billion light-years away forward by another 200 million light-years, allowing it to see galaxies 13.6 billion light-years away. This shows that galaxies existed widely only 200 million years after the Big Bang, enriching and revising the original estimates of the Big Bang theory.

Moreover, the Webb telescope has also discovered a number of galaxies that are in the process of collision and merger, such as the ZW96 galaxy located 500 million light years away in the constellation of Phylum; the spectacular HCG92 Hickson Compact Galaxy Group, also known as the Stephen Quintet; the IC1623 galaxy, etc. These larger galaxies that are being formed in the collision show that galaxy collisions in the universe are common, and almost all large galaxies are born in collisions and mergers.

These collision states actually preview the collision scene between the Milky Way and the Andromeda Galaxy in 3 billion years. It can be seen that galaxy collision is not a process of one galaxy swallowing another galaxy, but a process of collision and merger, a process of strong and weak combination or strong and strong combination, and a win-win situation.

This is my opinion, welcome to discuss and comment. Spacetime Communication original copyright, please do not infringe or plagiarize, thank you for your understanding and support.