Scientists have found the largest galaxy. How big is it? It will subvert your imagination

Recently, scientists discovered a giant galaxy in the universe. It may sound scary, but let's share it with you. We can also take this opportunity to popularize some basic knowledge about galaxies.

First, let's understand what a galaxy is. A galaxy is a celestial structure that is ubiquitous in the universe. It is a large system formed by a bunch of stars squeezed together, commonly known as a cosmic island. There are various explanations for the formation of galaxies, and there is no definitive answer. But it is generally believed that galaxies were formed about 1 billion years after the Big Bang. However, the Hubble Telescope has photographed galaxies that were being formed 450 million years after the Big Bang, so the formation time of galaxies should be earlier.

The standard model of modern cosmology holds that the universe was born in an explosion about 13.8 billion years ago. After the Big Bang, the universe has been expanding, and the temperature has gradually cooled down from the initial extreme high temperature until 380,000 years after the Big Bang, when the temperature and density dropped to allow the formation of neutral atoms. The universe that just formed elements only had hydrogen and helium, and a very small amount of lithium. These elements condensed with each other under the action of gravity and gradually formed large nebulae, and the original galaxy was formed in this way.

The nebula clusters of the original galaxies contracted more and more tightly, and on the other hand, they continuously absorbed the surrounding hydrogen and helium, and their mass became larger and larger. Due to the uneven contraction and the mutual movement between the nebula clusters, the original galaxies gradually rotated, and those that rotated faster became disk-shaped or spiral-shaped, and some became elliptical.

As the density of the original galaxy cloud cluster increased, small nebula clusters gradually formed independently inside due to the force of gravity. These small nebula clusters continued to shrink and gradually formed stars.

The main body of the galaxy is stars. After stars are formed, they will absorb the surrounding nebula dust, so the space between stars will become more and more empty.

However, stars and nebulae are only visible matter in the universe. Modern research has found that visible matter only accounts for 4.9% of the universe, and the remaining 95.1% is invisible dark matter and dark energy. Therefore, dark matter and dark energy dominate the universe, and the gravitational force of dark matter is the main force that maintains the shape of galaxies.

Galaxies generally do not exist alone, but always exist in groups under the interaction of gravity. The smallest group is called a galaxy group or cluster, and the larger group is called a supercluster. Even larger groups are called super-superclusters, all the way to huge celestial structures and the observable universe. For example, our Milky Way galaxy is a group formed by more than 50 galaxies, which scientists call the "Local Group."

In this group, the Andromeda Galaxy is the largest, the Milky Way is the second, and the Triangulum Galaxy is the third. The remaining 40 or so dwarf galaxies are relatively small and orbit the largest and second largest galaxies, so they can be regarded as satellite galaxies of the largest and second largest galaxies.

The Local Group is combined with hundreds of galaxy clusters to form a supercluster, of which the Local Group is a very small group. The largest galaxy cluster at the core of the supercluster is the Virgo Cluster, which contains more than 2,500 galaxies. Above the Local Supercluster is the Laniakea Supercluster, which contains more than 100,000 galaxies. I call this level of structure a super-supercluster.

Above this there is an even larger celestial system structure. The entire universe is stacked up layer by layer, all the way to the observable universe radius of 46.5 billion light years.

The large-scale structure of the universe is fibrous or mesh-like, a bit like dried loofah. Young people today probably rarely see loofah, which is the flesh inside the loofah that has grown up and dried and peeled off. In the early years, many rural areas used it to wash pots or make insoles.

The fibrous structure of galaxies is the fiber that makes up the universe of all galaxies, just like the "net" of a "loofah". The holes between the "loofah" are the extremely vacuum space in the universe. Almost all the matter inside has been sucked away by gravity. Even dark matter does not exist, but there is still weak microwave background radiation.

The universe is isotropic, meaning that no matter which direction you look from Earth, the universe looks the same, and the number of galaxies is also about the same. According to scientific observations such as the Hubble Space Telescope, astronomers have calculated that there are at least hundreds of billions to trillions, or even more than 10 trillion, of galaxies in the observable universe.

There are many ways to classify galaxies, which are mainly divided into three categories, namely elliptical galaxies, spiral galaxies, and irregular galaxies. According to Hubble's galaxy classification, E represents elliptical galaxies, S represents spiral galaxies, and Irr represents irregular galaxies.

Elliptical galaxies are classified into E0 to E7. E0 is close to a circle, and then from E1 onwards, it becomes more and more elliptical, and E7 is very thin and long. But no matter from which angle these galaxies are viewed, they have an elliptical appearance and no obvious structure.

Elliptical galaxies are generally older, and because they are very old, they have absorbed more and more cosmic matter, or they are formed by the collision and merger of multiple galaxies. In many galaxy clusters, there is an elliptical galaxy in the core, which is the main gravitational source of the galaxy.

The most typical feature of an elliptical galaxy is that old stars account for the vast majority, and new stars are no longer formed or are formed very rarely.

A spiral galaxy is a discus-shaped disk galaxy with a bulge in the central region and a thinner edge. Several spiral arms extend from the nucleus around the core bulge, extending to the edge of the galaxy in a spiral curve, like a windmill or typhoon structure.

Spiral galaxies are divided into two types: normal spiral galaxies and barred spiral galaxies. Normal spiral galaxies are further divided into three shapes: a, b, and c. Type Sa galaxies have a large central region, and the spiral arms are sparse and tightly coiled; Type Sb galaxies have a smaller central region, and the spiral arms are larger and more spread out; Type Sc galaxies have a bright central region, and the spiral arms are large and loose.

A barred spiral galaxy is a spiral galaxy with a bar-shaped light column in the center. Its spiral arms are different from those of a normal spiral galaxy, which emerge from the core. They appear to emerge from both ends of the bar. About two-thirds of spiral galaxies are barred spiral galaxies. Our Milky Way is a barred spiral galaxy.

Irregular galaxies are irregular in shape, without obvious nuclei and spiral arms, and are represented by Irr. Irregular galaxies account for about 5% of all galaxies. They are relatively small galaxies, generally only 100 million to several billion times the mass of the sun, and rarely up to 10 billion times the mass of the sun. Therefore, this type of galaxy is also called a dwarf galaxy. This type of galaxy is divided into Type I and Type II. Type I has a little spiral; Type II has no rules and is a mess.

In addition, there is another type of galaxy called lens galaxy, denoted by S0. This type of galaxy is a transitional galaxy from an elliptical galaxy to a spiral galaxy or a barred galaxy. As the dark matter in it continues to expand, it has the function of a natural lens, which plays an important magnifying role in astronomers' observation of distant celestial bodies.

The ratio of various galaxies in the universe is roughly: elliptical galaxies account for about 15%, spiral galaxies account for about 80%, and irregular galaxies account for about 5%. This is just a saying, and some studies are inconsistent with this ratio. In addition, there are not many lenticular galaxies discovered so far, so they are not included in the ratio.

So, which is the largest galaxy? In terms of levels, the closest large galaxy to us is the Andromeda Galaxy (M31), which is a spiral galaxy, but unlike our Milky Way, it does not have a bar-shaped light column at its core, so it is a more typical spiral galaxy and the largest galaxy in the Local Group. Its disk diameter is about 220,000 light years, its mass is about 7.1*10^12 solar masses (including dark matter), and the number of stars is about twice that of the Milky Way.

Since many elliptical galaxies are formed by the merger of several galaxies, their huge gravitational force will continue to attract many satellite galaxies to join, and they are very old, so they will grow very large. In the core of our Super Cluster, in the center of the Virgo Cluster, there is a huge elliptical galaxy called M87.

There is a huge black hole at the core of the M87 galaxy, which caused a sensation in 2017. The black hole in the first black hole photo taken by humans has a mass of 6.5 billion solar masses. This galaxy is about 55 million light years away from us, which means that it takes 55 million years for light to reach us. The mass of the entire galaxy is about 2.6*10^12 solar masses, which probably does not include the mass of dark matter, that is, the mass of visible matter. The visible mass of the Milky Way is about 2*10^11 solar masses, which is at least 13 times larger than the mass of the Milky Way.

But this kind of galaxy is still a small one in the universe. As early as 1931, Edwin Hubble, the scientist who discovered the expansion of the universe, discovered a huge elliptical galaxy. This galaxy 1.045 billion light-years away from us was named "IC 1101". It was not until 1991 that scientists measured that the diameter of this galaxy was only 6 million light-years.

However, there is controversy in the scientific community over this estimate. Even based on the least controversial estimate of 2 million light-years, this galaxy is terrifyingly large, more than 10 times the diameter of the Milky Way. It contains at least 100 trillion stars, and the core that emits powerful radio sources is a supermassive black hole with an estimated mass of 40 to 100 billion solar masses.

Just in February of this year, the website of the American magazine "Popular Science" published a report: Scientists at the Leiden Observatory in the Netherlands discovered the largest galaxy ever observed. The scientists called this galaxy "Alcyoneus", which is the name of a giant in ancient Greek mythology.

The research report said that this galaxy is 3 billion light years away from the Earth, with a diameter of 16.3 million light years and a mass of about 240 billion times that of the Milky Way. What does this mean? If the star types of the Alcyoneus galaxy are similar to those of the Milky Way, then according to mass, the Milky Way has 400 billion stars, while the Alcyoneus galaxy has 960 trillion trillion stars.

Oh my god, this is too subversive. There is also a radio source at the core of this galaxy, that is, there is a supermassive black hole, but compared with the mass of the galaxy, this black hole is very ordinary, with a mass of only 400 million times that of the sun, only 1/16 of the M87 black hole, and 1/100~250 of the IC 1101 black hole.

Is this the largest galaxy in the universe? It can be said that it is definitely not, because human beings' current discovery and understanding of the universe is still very shallow. I believe that with the improvement of scientific observation methods, more and larger galaxies will be discovered in the future. What do you think? Welcome to discuss, thank you for reading.

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