Milky Way

Our galaxy, called the Milky Way because it looks like a jet of milk in the night sky, has long been a great unknown. In 1610, the Italian astronomer Galileo Galilei was the first to point a telescope at the night sky and noticed that a faint whitish belt consisted of many thousands of stars, which seemed to touch each other. In time, astronomers realized that all these stars, as well as the Sun, were part of a huge whole - the Milky Way galaxy.

The diameter of the Milky Way is between 100,000 and 180,000 light-years. Its age is difficult to determine, but it is estimated at approximately 13.6 billion years. The Milky Way belongs to a cluster of about thirty galaxies and after the Andromeda galaxy (the largest galaxy closest to us, approximately 2.5 million light-years away) is the largest in the entire group. Until the end of the 1920s, the Andromeda galaxy was thought to be part of our galaxy, until the American astronomer Edwin Hubble proved that it was a separate system.

It is not possible to determine exactly which type of galaxy the Milky Way belongs to. It is a spiral galaxy and, according to Hubble's division, belongs to the type Sb or Sc (spiral galaxy with a smaller core and more open branches), but recent research shows that the Milky Way has an obstacle (or at least something that looks like an obstacle in structure) in the central region . According to that, the Milky Way belongs to the type SB (spiral barbed galaxy), ie. in some intermediate type SBb or Sbc (between a normal spiral galaxy and a spiral galaxy with a bar).

The composition of the Milky Way

The Milky Way, which is estimated to contain between 100 billion and 400 billion stars, has four spiral branches that revolve around its core. In Sagittarius branch, which is located between the Orion branch and the center of the Milky Way, there is one of the brightest stars in that galaxy, Eta Pramca. There are young stars and nebulae in Perseus' branch, the main outer branch of the Milky Way. In the Orion branch, which stretches between Perseus and Sagittarius, is the solar system, at a distance of 26,000 light-years from the center of the galaxy. The Orion branch is a real factory for the production of stars, where billions of new stars can be formed from gaseous interstellar matter. It also contains the remains of former stars.

The brightest part of the Milky Way in photographs taken with optical lenses (which record visible light) is located in the constellation Sagittarius. The bright band in the night sky, which most likely extends towards the center of the galaxy, consists of so many stars that it is impossible to count them. In some cases, the stars are obscured by a thick cloud of dust, which makes some parts of the Milky Way very dark (dark areas in the night sky).

The speed of rotation of different parts of the Milky Way depends on the distance of these parts from the center of the galaxy. Most stars are concentrated in the space between the center of our galaxy and its periphery. There, the speed of rotation is much higher due to the attractive effect of billions of stars on objects located in that space. The speed of rotation decreases with increasing distance from the center of the galaxy.

Central region of the Milky Way

Seen from Earth, the center of the Milky Way is in the constellation Sagittarius. So far, no image has been made of the very center of our galaxy due to gas clouds and interstellar dust that are around it. However, the center can be seen through telescopes that record infrared light, radio waves or X-rays because they can pass through matter that blocks visible light. The central axis, which contains ancient stars about 12 billion years old, shows intense activity in the interior, where there are two gas clouds: Sagittarius A and Sagittarius B. These gas clouds are associated with strong activity at the center of our galaxy and hide the heart of the Milky Way. In the center of the Milky Way, there is the largest concentration of stars, old, red and orange giants, whose diameters are larger than 100 to 200 times larger than the Sun. Many astronomers assume that there is a massive black hole in the center of the Milky Way surrounded by a large layer of cosmic dust. Namely, the center of our galaxy is surrounded by a strong magnetic field, which probably originates from a rotating black hole.

Moving away from the center, you come across young, blue stars. In addition to individual stars, which are impossible to count, the Milky Way also abounds in a large number of star clusters, nebulae and multiple star systems. It is estimated that there are about 200 compacted star clusters in it, and so far over 150 have been discovered. The most beautiful such star cluster is the Hercules cluster in the constellation Hercules, about 23,000 light-years away. Nebulae, which represent perhaps the most beautiful phenomenon in the sky, are divided into light and dark, and the difference in brightness depends on the position of the star that illuminates them. The best example of a light nebula is the Great Orion Nebula, which can be seen with the naked eye, and for the dark nebula Horsehead NGC 2024, which is located near the star Zeta Orion in the constellation Orion.

Milky Way satellites

The Milky Way, like other galaxies, has its satellites, which are:

1) Small Magellanic Cloud - seen only from the southern hemisphere, and is a small irregular galaxy designated NGC 292. It orbits the Milky Way at a distance of 210,000 light-years, making it the third closest galaxy, after the Large Magellanic Cloud and the Dwarf Elliptical galaxies.

2) Large Magellanic Cloud - also seen only from the southern hemisphere, and is a small irregular galaxy that orbits the Milky Way at a distance of 179,000 light-years. Until 1994, when the Dwarf Elliptical Galaxy was discovered, it was thought to be the closest galaxy to us. Like the Little Magellanic Cloud, this galaxy is full of interesting objects, such as diffuse nebulae, dense and scattered star clusters, planetary nebulae.

3) Dwarf elliptical galaxy - that galaxy in the constellation Sagittarius represents the closest galaxy to us, which is located at a distance of 80,000 light years. A team of astronomers from Johns Hopkins University discovered in February 1998 that the galaxy had been orbiting the Milky Way for about a billion years.

Basic data of the Milky Way galaxy

• Age: 13.6 billion years

• Diameter: 100,000 - 180,000 light years

• Center diameter: 10,000 light years

• Mass: 0.8–1.5 × 1012 solar masses

• Number of stars: 100 billion - 400 billion

• Distance of the Sun from the center of the galaxy: 26,000 light years

• Sun orbital time around the center of the galaxy: 225 million years