A galaxy is a gravitationally connected system of stars, dust, gas, and dark matter. It is estimated that there are almost 3.9 trillion of them in the Universe. One of them - the Milky Way is our home, it is here that the Sun was created about 4.57 billion years ago and around which our planet was formed.
The Milky Way was formed by the merger of several clumps of matter formed shortly after the Big Bang. Over time, it merged and absorbed other galaxies, increasing in size. It is estimated that almost half of the matter in the Milky Way comes from distant galaxies. The process of absorbing new ones continues constantly, and in about 3.75 billion years the Milky Way will collide with one of the larger galaxies in our cosmic neighborhood - M31 Andromeda.
Its age is estimated at 13.6 ± 0.8 billion years, so it may be only 100 million years younger than the Universe.
Previously, it was believed that it could be part of the Earth's atmosphere or underexposed stars (it was believed that stars shine with light reflected from the Sun) that were in the Earth's shadow.
Only observations made by Edwin Hubble made humanity realize that it is only one of many galaxies.
It is therefore a relatively large galaxy, although some cosmic giants may dwarf it in size. IC 1101 is about 20 times larger than the Milky Way, with a diameter of 2 million light-years.
It is an area spanning 10 million light years and located in the Laniakea supercluster. We do not know its exact location in the Universe because our eyes only see the image of the Visible Universe, which is only a fragment from which we can receive the electromagnetic radiation reaching us.
The number of stars was originally estimated at around 100 million, but recent measurements suggest that this number may be up to four times greater.
It interacts with visible matter only gravitationally and remains invisible and undetectable in any other way. It is estimated that 90 percent of the mass of the Milky Way is dark matter.
The halo consists of old stars and globular clusters, and 90 percent of the material it contains is located within a radius of 100.000 light years from the center of the Milky Way.
Its temperature is from 1 million to 2.5 million degrees Celsius and it extends for hundreds of thousands of light-years from the galactic center to the neighboring satellite galaxies - the Small Magellanic Cloud and the Large Magellanic Cloud, and its mass is almost equal to the mass of the Milky Way itself.
It lasts about 230 - 240 million years. The solar system moves around the center of the Milky Way at an average speed of 230 km/s (828,000 km/h).
It is located on the inner side of the Orion Arm, one of at least four arms of the galaxy. Their exact number is difficult to determine because we are inside the Milky Way and a large part of it is obscured by its internal structures, making precise measurements impossible.
A bright band of stars, gas, and dust runs through the center of the galaxy (forming a bar), with arms emerging from the ends. There are at least four main arms in the Milky Way: Sagittarius, Carboniferous, Perseus, Cross, and several smaller ones: Orion (where the Solar System is located), the Near Three-Kiloparsec Arm, and the Far Three-Kiloparsec Arm.
This region, called Sagittarius A*, is a very bright and compact radio source with a mass of 3.7 million solar masses and a diameter of approximately 44 million kilometers.
This dwarf galaxy is located 42.000 years ago. light years from the center of our galaxy and 25 thousand. light years from the solar system. It was discovered in November 2003 because it is hidden behind the Milky Way's clouds of dust and gas. It contains about 100 million stars and is currently being torn apart by our galaxy's gravity.
All these objects are within the range of the Milky Way's gas halo and are its satellites. The largest of them are the Large Magellanic Cloud, SagDEG, Ursa Major II, and Toucan II.
Unfortunately, it cannot be observed directly in the visible spectrum because it is obscured by clouds of dust and gas. Observations of this region are therefore carried out in the ranges of radio, millimeter waves, infrared, hard X-rays (from 5 to 100 pm), and gamma radiation.