Star Cluster: Definition, Features and Species

On the night sky in clear weather you can see a lot of small glowing lights - the stars. In fact, their dimensions can be enormous and hundreds, or even thousands, of times the size of the Earth. They can exist separately, but sometimes they form a star cluster.

What are stars?

The star is a massive ball, consisting of gas. It is able to withstand the force of its own gravity. The star mass, as a rule, is greater than the planetary mass. Within them, thermonuclear reactions occur that contribute to the emission of light.

The stars are formed mainly from hydrogen and helium, as well as dust. Their internal temperature can reach millions of Kelvin, although the external one is much smaller. The main characteristics for measuring these gas balls are: mass, radius and luminosity, that is, energy.

With the naked eye, a person can see about six thousand stars (three thousand in each hemisphere). The closest to the Earth we see only in the day is the Sun. It is located at a distance of 150 million kilometers. The star closest to our solar system is called Proxima Centauri.

The birth of stars and clusters

Dust and gas present in unlimited quantities in interstellar space can be compressed under the action of gravitational forces. The denser they contract, the greater the temperature is formed inside. Sealing, the substance accumulates mass, and if it is sufficient to carry out a nuclear reaction, a star will arise.

A gas-dust cloud often forms several stars, which capture each other in the gravitational field and form stellar systems. Thus, there are double, triple and other systems. More than ten stars form a cluster.

Star cluster represents a group of stars of common origin, which are connected with each other by gravity, and move in the field of the galaxy as a single whole. They are divided into spherical and scattered. In addition to stars, clusters can contain gas and dust. Combined by common origin, but not bound by gravity, groups of celestial bodies are called stellar associations.

History of discoveries

People from ancient times watched the night sky. However, for a long time it was believed that the heavenly bodies were evenly distributed in the expanses of the Universe. In the 18th century, the astronomer William Herschel challenged science, saying that in some parts of the stars there was clearly more than in others.

A little earlier, his colleague Charles Messier noted the existence of nebulae in the sky. Watching them through a telescope, Herschel found out that this was not always the case. He saw that sometimes a stellar nebula is a cluster of stars that seem to be spots, if you look at them with the naked eye. He called it "heaps". Later, another name was invented for these phenomena of the galaxy - star clusters.

Herschel managed to describe about two thousand clusters. In the XIX century, astronomers determined that they differ in shape and size. Then, spherical and scattered clusters were isolated. A detailed study of these phenomena began only in the twentieth century.

Scattered Clusters

Between each other, clusters differ in the number of stars and in the form. A scattered star cluster can include ten to several thousand stars. They are young enough, their age can be only a few million years. Such a star cluster does not have clearly defined boundaries, it is usually found in spiral and irregular galaxies.

About 1,100 clusters are found in our galaxy. They do not live long, because their gravitational connection is weak and can easily burst due to passing gas or other clusters near the clouds. The "lost" stars become single.

Clusters are often found on spiral arms and near galactic planes - where the concentration of gas is greater. They have uneven shapeless edges and a dense, well-distinguishable core. Scattered clusters are classified in accordance with the density of placement, differences in the brightness of internal stars, as well as distinctness in comparison with the environment.

Globular Clusters

Unlike the scattered stars, the globular star clusters have a distinct spherical shape. Their stars are connected by gravitation much more closely, and revolve around the galactic center, playing the role of satellites. The age of these clusters is many times greater than the scattered ones, amounting to 10 billion years or more. But in terms of quantity they are much inferior, in our galaxy there are still about 160 globular clusters.

They contain from tens of thousands to a million stars, the concentration of which increases toward the center. They are characterized by the absence of gas and dust, since they formed long ago. All stars of globular clusters are approximately at one stage of development, and so they were formed, as well as scattered, at about the same time.

The high density of stars in the cluster often leads to collisions. As a result, unusual classes of luminaries can be formed. For example, when the members of the binary star system merge, a blue straggling star appears. It is much hotter than other blue stars and clusters. In the course of the collision, another exotic cosmic space may emerge, such as low-mass X-ray binary stars and millisecond pulsars.

Star associations

Unlike clusters, star associations are not connected by a common gravitational field, sometimes it is present, but its forces are too small. They appeared at one time and have a small age, reaching tens of millions of years.

Star associations exceed in size young scattered clusters. They are more rarefied in outer space, and include up to hundreds of stars in their composition. About a dozen of them are hot giants.

A weak gravitational field does not allow stars to stay in association for a long time. For disintegration, they need from several hundred thousand to a million years - by astronomical standards this is negligible. Therefore, stellar associations are called temporal formations.

Known congestions

A total of several thousand star clusters were discovered, some of them visible to the naked eye. The closest to the Earth are the scattered clusters of the Pleiades (Stozhary) and the Hyades, located in the constellation of Taurus. The first contains about 500 stars, without special optics of them only seven are distinguishable. The Hyades are next to Aldebaran and contain about 130 bright and 300 weak-flung participants.

The scattered star cluster in the constellation of Cancer is also one of the nearest. It is called Nursery and contains more than two hundred members. Many characteristics of the Yasley and Hyades coincide, so there is a possibility that they are formed from one gas-dust cloud.

It is easily discernible in binoculars star cluster in the constellation of Veronica's hair in the northern hemisphere. This globular cluster M 53, opened as far back as 1775. It is located at a distance of more than 60,000 light years. The cluster is one of the most remote from the Earth, although it is easily discernible in binoculars. A huge number of globular clusters are located in the constellation Sagittarius.

Conclusion

Star clusters are large groups of stars, united by gravity forces. They number from ten to several million stars, which have a common origin. Basically, ball and scattered clusters are distinguished, differing in shape, composition, size, number of members and age. In addition to these, there are temporary clusters, called stellar associations. Their gravitational connection is too weak, which inevitably leads to the decay and formation of ordinary single stars.