How many galaxies are there in the universe?

Star system, or galaxy, is an "island" of giant stars in the universe, and it is also one of the largest and most beautiful celestial systems in the universe. So far, people have observed about 1000 billion galaxies in the universe. Some are close to us, and their structures can be clearly observed; Some systems are very far away, and the farthest known systems are nearly 20 billion light years away.

According to the Big Bang theory, the first generation of galaxies was formed about one billion years after the Big Bang. At the initial moment of the birth of the universe, there was an explosion of primitive energy. With the expansion and cooling of the universe, gravity began to play a role, and then the young universe entered a short stage called "skyrocketing". With the rapid expansion of the universe, the small fluctuations in the original energy distribution have been greatly amplified from the micro-scale, thus forming some "trenches" along which galaxy clusters are formed.

Photographs of distant young galaxies taken by Hubble Space Telescope contain clusters of galaxies (protogalaxies) in the process of formation.

Individual photos of eighteen emerging clusters of galaxies. Each group is about10 billion light-years away from the earth.

The famous "Hubble Deep Space" photo. It shows more than 1000 young galaxies formed in less than1000 billion years after the formation of the universe.

Hubble deep space picture. The arrow may point to the most distant galaxy discovered so far.

Abel 22 18 Galaxy Group. The photo reflects the phenomenon of "gravitational lens" in the universe.

Two adjacent galaxies NGC 14 10 and NGC 1409 absorb each other due to gravity.

With a brief expansion, the universe returned to the usual expansion speed seen today. In the first second after the birth of the universe, with the continuous expansion and cooling of the universe, a large number of protons, neutrons and electrons condensed from the background energy in the "dense" region. After a hundred seconds, protons and neutrons began to combine to form helium nuclei. In less than two minutes, all the atomic components that make up nature were produced. About 300,000 years later, the universe has cooled to the point where hydrogen and helium nuclei are enough to capture electrons and form atoms. These atoms slowly gather into huge fibrous clouds under the action of gravity. Soon, galaxies formed in it. One billion years after the Big Bang, hydrogen clouds and helium clouds began to gather together under the action of gravity. As the cloud grows, primary galaxies or protogalaxies begin to form. At that time, the universe was very small and the protogalaxies were very close, so the interaction was very strong. As a result, some smaller clouds condense into thinner and larger clouds, while others are swallowed up by neighboring clouds.

At the same time, due to the continuous falling of hydrogen and helium, the protogalaxy gradually became larger. The greater the mass of the protogalaxy, the more gas it attracts. The movement of each cloud cluster and the interaction between them eventually make the protogalaxy start to rotate slowly. These clouds further collapse under the action of gravity, and some clouds with faster rotation form disks; The rest are roughly oval. After getting enough material, these primitive galaxies began to form stars in them. At this time, the appearance of the universe is similar to today. Galaxies gather together in groups, just like islands in our earth's ocean, embedded in the vast space gas cloud. This cluster and intergalactic gas stretch into a fiber structure, which can reach hundreds of millions of light years in length. Such a large-scale cluster of galaxies is spherical in the vast space.

No two galaxies in the universe are exactly the same in shape, and each galaxy has its own unique appearance. However, because galaxies are all formed in a limited range of conditions, they have some common characteristics, which enables people to classify them roughly. Among the various classification systems of galaxies, the classification system proposed by astronomer Hubble in 1925 is the most widely used one. Hubble divides galaxies into three categories according to their shapes: elliptical galaxies, spiral galaxies and irregular galaxies. Elliptic galaxies can be divided into seven types, which are expressed by E0-E7 according to the oblateness of galaxy ellipses from small to large, and the maximum value of 7 is arbitrary. This classification is limited to the shape of galaxies seen from the earth, because the angle of elliptical galaxies in space is difficult to determine. Spiral galaxies are divided into two groups. One group is a rod-like spiral galaxy with a rod-like structure in the center, which is represented by SB. The other is a spiral galaxy without a rod structure, which is denoted by S. These two types of galaxies are subdivided into three subtypes, and the subscripts A, B and C denote the size of the galactic nucleus and the tightness of the spiral arm respectively. Irregular galaxies have no certain shape and contain more dust and gas, which is expressed by Irr. Another lens galaxy, denoted by S0, represents a transitional galaxy between an elliptical galaxy and a spiral galaxy.

NGC4552 belongs to E0 elliptical galaxy. The galaxy is located in Virgo.

NGC4486 is also located in Virgo and belongs to E 1 elliptical galaxy.

NGC4479 belongs to E4 elliptical galaxy and is located in Virgo.

NGC205 elliptical galaxy, belonging to E6 type, is located in Andromeda.

NGC3 1 15, located in sextant, belongs to E7 elliptical galaxy, and some people classify it as S0 type.

NGC3623 is located in Leo and belongs to Sa spiral galaxy.

Sb NGC3627 spiral galaxy is located in Leo.

The spiral galaxy NGC5 194 in Canine constellation belongs to Sc type. On the left is a dwarf galaxy.

NGC335 1, located in Leo, belongs to the SBb-type rod spiral galaxy.

SBc rod spiral galaxy NGC3992 is located in Leo.

The satellite system of the Milky Way is the Large Magellanic Cloud, which is an irregular galaxy.

NGC3034 is an irregular galaxy located in Ursa Major.

Most large galaxies in the universe are spiral galaxies, followed by elliptical galaxies, and irregular galaxies account for the smallest. Spiral galaxies rotate faster, and their disks contain a lot of dust and gas, which gather into a region where stars can form. These areas have developed spiral arms containing many blue stars, so the color of the disk looks blue. However, many ancient stars are densely distributed in its rod-like structure and central nuclear sphere. Compared with spiral galaxies, elliptical galaxies have very slow rotation speed, uniform and symmetrical structure, no spiral arms and little dust and gas. The reason for this is that as early as billions of years ago, when stars formed rapidly, all the dust and gas in elliptical galaxies were consumed. Therefore, new stars cannot be born in these galaxies, so all elliptical galaxies contain old stars.

There are about one billion galaxies in the universe with a supermassive black hole in the center. Such galaxies are called "active galaxies". Quasars also belong to this kind of galaxy.

In addition, there is a dwarf galaxy. Such galaxies are not as bright as big ones, but they are numerous. There are many dwarf galaxies near the Milky Way, more than all other types of galaxies combined. A large number of dwarf galaxies have also been found in nearby galaxy clusters. Some of them are regular in shape, and most of them contain the second group of stars. Irregular dwarf galaxies usually contain bright blue stars.

The shape of galaxies is generally determined at birth, and has remained relatively stable since then, unless there is a collision between galaxies or the gravitational interference of neighboring galaxies.

On a clear night without light interference, if the sky is dark enough, you can see the diffuse light bands in the sky. This band of light is what we see when we look at the Milky Way from the inside. It is a round surface full of stars-a silver disk. There are about 200 billion stars in the Milky Way, but they are too far away to be recognized by the naked eye. Because starlight is mixed with interstellar dust gas, it looks like a band of light shrouded in smoke. The center of the Milky Way lies near Sagittarius.

The Milky Way is a medium-sized star system, and its silver disk is about120,000 light years in diameter. Its silver disk contains a lot of interstellar dust and gas clouds, which gather into a red star-forming area, thus constantly supplementing the spiral arms of galaxies with hot young blue stars, forming many open clusters or clusters of galaxies. There are more than 1200 such open clusters. Around the silver disk is a huge silver halo dotted with stars and globular clusters mainly composed of old stars.

Swan-the Milky Way of Sagittarius.

Bright galactic center (silver core) part.

Brilliant galactic center (silver core) Part II.

Vega, Altair-the Milky Way of Sagittarius.

Skyhawk-the Milky Way of Sagittarius.

Long shield-a galaxy in the direction of Sagittarius.

From our point of view, it is difficult to know exactly the shape of the Milky Way. However, with the development of modern science and technology, the progress of detection means has overcome these obstacles to some extent and revealed some unexpected characteristics of the Milky Way. For a long time, people thought that the Milky Way was a typical spiral galaxy, similar to Andromeda. However, recent observations show that its central nuclear sphere is slightly rod-shaped. This means that the Milky Way galaxy is probably a rod-spinning galaxy. In addition, the Milky Way is a relatively active galaxy, the silver core has strong cosmic ray radiation, and the stars rotate at high speed around an invisible center. This shows that there is a supermassive black hole in the core of the Milky Way.

The Milky Way has two smaller neighbors-large magellanic cloud and small magellanic cloud, both of which belong to irregular galaxies. Because of gravity, the Milky Way constantly absorbs dust and gas from these two small galaxies, making the matter in these two neighbors less and less. It is predicted that after10 billion years, the Milky Way will devour all the materials in these two galaxies, and these two close neighbors will no longer exist.