Galaxies have no clear boundaries. Sometimes it is very difficult to do because of the remoteness of the observed cluster of stars.
What is a galaxy?
Translated from Greek, the word "galaxy" means "Milky Way." This is the name of a system of stars interconnected by gravity and their clusters, planets, interstellar gas and dust, dark matter. All these objects move in relation to a certain center of mass.
We can observe our own galaxy in the form of a long elongated strip densely strewn with stars. All other clusters are very remote. Their distances from the Earth are measured in megaparsec (3.2 million light years). Distances to very distant galaxies are measured in units of metagalactic redshift.
In the observed part of the Universe (i.e., the part in which matter managed to reach its present place, in this case of the Earth for all existence), apparently, there are at least 2 trillion. galaxies. Without a telescope, you can see:
- Andromeda nebula observed in our hemisphere;
- large and small Magellanic clouds (observed in the opposite hemisphere);
Galaxy M33.
It is impossible to distinguish them from stars without telescopes. The weight of galaxies exceeds solar by billions, or even trillions of times. Their diameter can exceed 800 thousand light years.
Dark matter is an unsolved problem of the structure of galaxies. It is detected only in the process of gravitational interaction.It is believed that 90% of the mass of the object in question is precisely dark matter.
What is the center of the galaxy?
The physical properties of its center differ significantly from the boundaries and from the surrounding areas of space. For a long time, the nature of the galactic center has been a mystery to scientists.
More recently, scientists have found that in the central region of the galaxy is a black hole. In this space, the attraction is so huge that its surface cannot leave an object moving at the speed of light. The processes of star formation in galaxies continue.
Galaxy borders
In all observed galaxies, clear boundaries are not defined. This means that it is impossible to say exactly where the galaxy ends and intergalactic space begins. Moreover, if in a certain optical range it has any one size, then according to the analysis of observations of interstellar gas it can be several times larger.
Intergalactic space is understood to mean the part of the Universe that is located between galaxies. There is practically no matter in it. Its average density is less than a hydrogen atom per 1 cubic meter. dm. This means that 1 gram of hydrogen atoms is contained in 100 billion cubic kilometers of space. If it was filled with water, it would weigh 100 billion billion tons.
New in defining boundaries
Astronomers working at the University of Cambridge managed to detect the boundaries of the galaxy. They showed that dark matter is unusual in them.
In the galaxy in the constellation Ursa Minor, stars slowly moving around the center were discovered. It turned out that they are fragments of a globular cluster. Their presence is contrary to the prevailing theory that the density of dark matter grows closer to the galactic center. If this were so, then the remnants of the globular cluster would not have been discovered.
Constant observations of this galaxy made it possible to establish its boundaries. This is a surface where there is no dark matter. At the same time, studying the movement of stars leads to the conclusion that such a substance can be far beyond where there are stars.
Since the stars move weakly in the galaxy in question in its remote parts, there is little dark matter in the halo surrounding it. It is possible that part of it “came off” by another closely located galaxy. It is possible that all the stars have ever been thrown off the center under the influence of forces unstudied until today.
This is the first case of reliable detection of the boundaries of the galaxy. Their definition is a mystery to astronomers. Perhaps using the latest technology will help solve this problem.
