Galaxies and metagalaxies
In one of his speeches, A. Einstein said (in 1929): “To be honest, we want to not only find out how it works, but also if possible to achieve the goal of a utopian and daring-looking – to understand why nature is such. “This is the Promethean element of scientific creativity.”
Galaxies have been the subject of cosmogonic research since the 1920s, when their true nature was reliably established, and it turned out that these are not nebulae, i.e. not clouds of gas and dust, which are not far from us, but huge star worlds lying from us at very great distances from us. Discoveries and research in the field of cosmology have clarified in recent decades much of what concerns the background of galaxies and stars, the physical state of discharged matter from which they formed in very distant times. The whole of modern cosmology is based on one fundamental idea – the idea of gravitational instability dating back to Newton. A substance cannot remain uniformly scattered in space, because the mutual attraction of all particles of a substance strives to create in it condensations of various scales and masses. In the early Universe, gravitational instability intensified initially very weak irregularities in the distribution and movement of matter and in a certain era led to the emergence of strong heterogeneities: “pancakes” – proto-clusters. The boundaries of these compaction layers were shock waves, at the fronts of which the initially non-rotational, irrotational motion of matter acquired a vorticity. The disintegration of layers into separate condensations also occurred, apparently, due to gravitational instability, and this gave rise to protogalaxies. Many of them turned out to be rapidly rotating due to the swirling state of the substance from which they were formed. Fragmentation of protogalactic clouds as a result of their gravitational instability led to the appearance of the first stars, and the clouds turned into stellar systems – galaxies. Those of them that had fast rotation acquired a two-component structure because of this — they formed a halo of a more or less spherical shape and a disk in which spiral arms appeared, where the birth of Protogalaxy stars continues, where rotation was still slower or nonexistent, turned into elliptical or irregular galaxies. In parallel with this process, the formation of a large-scale structure of the Universe took place — superclusters of galaxies arose, which, when combined with their edges, formed the likeness of cells or honeycombs; they have been recognized in recent years.
In the years 20-30. XX century Hubble developed the basis for the structural classification of galaxies – giant stellar systems, according to which there are three classes of galaxies:
I. Spiral galaxies – are characterized by two relatively bright branches arranged in a spiral. Branches emerge either from a bright nucleus (such galaxies are denoted by S), or from the ends of a light jumper crossing the nucleus (denoted by SB).
The representative is the M82 galaxy in the constellation B. Dipper, does not have a clear outline and consists mainly of hot blue stars and gas clouds heated by them. M82 is 6.5 million light-years from us. Perhaps, about a million years ago, a powerful explosion occurred in its central part, as a result of which it acquired its current form.
The spiral galaxy M51 in the constellation of the Hounds of the Dogs is one of the most amazing spiral star systems. The distance to them is about 8 million light years. The thickening at the end of the spiral branch is an independent irregular galaxy. Separate bright stars are in our galaxy.
II. Elliptical galaxies (denoted by E) – having the shape of ellipsoids.
Representative – the ring nebula in the constellation Lyra is located at a distance of 2100 light years from us and consists of a luminous gas surrounding a central star. This shell was formed when an aging star dropped its gas cover and they rushed into space. The star shrank and turned into a white dwarf state, comparable in mass with our sun, and in size with the Earth.
III. Irregular (irregular) galaxies (denoted by I) – having irregular shapes.
Representatives – The Big Magellanic Cloud is located at a distance of 165,000 light years and, thus, is the closest galaxy to us in a relatively small size. Next to it is a smaller galaxy – the Small Magellanic Cloud. Both of them are satellites of our galaxy.
According to the degree of raggedness of the branches, spiral galaxies are divided into subtypes a, b, s. In the first of them – the branches are amorphous, in the second – a little ragged, in the third – very ragged, and the core is always dim and small.
In the second half of the 40s of the twentieth century, W. Baade (USA) found that the raggedness of spiral branches and their blueness increase with an increase in the content of hot blue stars, their clusters and diffuse nebulae.