We live on the third planet from a medium-sized star, two-thirds of the way from the center of the Milky Way in one of its spiral arms. But what place do we occupy in the universe? At the beginning of the XX century. Vesto Slipher studied the sky at the Lovell Observatory in Flagstaff, Arizona. Its director, Percival Lovell, was interested in finding planets around other stars and believed that the spiral nebulae that were being discovered at that time could be stars with new planetary systems forming around them.
To test this theory, Lovell invited Slipher to study the chemical composition of the spiral nebula using a spectrograph, which decomposes light into a spectrum. Using a 600mm refractor telescope, Slipher collected enough light for the spectrum of just one nebula over two nights. The result puzzled him: all spectra showed a strong red shift.
Only the work of Edwin Hubble at Mount Wilson Observatory has solved the mystery of this redshift. With a 2.5-meter reflector at their disposal, Edwin Hubble and Milton Humason obtained photographs of the neighboring spiral nebula so clear that by 1924 it became possible to split it into separate stars.
In 1929, Hubble showed that the redshift indicates that galaxies are moving away from us at a speed of hundreds of thousands of kilometers per second.
From his observations, Hubble concluded that fainter and therefore probably more distant galaxies show a greater redshift. Therefore, Hubble's law states that the redshift of galaxies increases in proportion to their distance from us. Measuring the redshift allows you to determine the distances in the universe.
Distribution of galaxies
Shortly after Hubble suggested that the universe was expanding, he stated that galaxies were evenly distributed. To prove this, the astronomer photographed many small areas of the sky using the same 2.5-meter reflector. With the exception of an area in the vicinity of the Milky Way, where dust obscured the galaxies, which he called the zone of avoidance, he found about the same number of galaxies everywhere.
Other cosmologists disagreed with Hubble. Harlow Shapley and Adelaide Ames noticed significant irregularities in the distribution of galaxies across the sky. In some areas there were many of them, in others - relatively few. Clyde Tombaugh, who discovered Pluto in 1930, confirmed the Shapley and Ames data and went further, finding in 1937 a cluster of hundreds of galaxies in the constellations Andromeda and Perseus.
Even more was achieved when creating the Palomar sky survey with a 1, 2-meter Schmidt telescope. Using his excellent photographic capabilities, George Abell showed that galaxies form clusters and superclusters.
Local group of galaxies
The Milky Way and the Andromeda galaxy are the largest members of a small group of 30 galaxies called the Local Group of Galaxies. This cluster is part of a supercluster of galaxies, other members of which can be seen in the constellations of Coma and Virgo.
Now there are other superclusters scattered throughout the universe, but are there clusters of superclusters? Recent observations with powerful telescopes give no reason to think so. Superclusters form huge cellular structures in space with vast voids between them. These gigantic expanding formations diverge as the universe expands. The galaxies in the clusters are bound by gravity, but the expansion of the Universe is uncontrollably moving the clusters apart.
A gravitational lens is a massive body (planet, star) or a system of bodies (a galaxy, a cluster of galaxies, a cluster of dark matter) that bends the direction of propagation of electromagnetic radiation with its gravitational field, just as an ordinary lens bends a light beam.
Double quasar In the late 1970s. in the photographs of the Palomar Sky Survey, two identical quasars were found, between which there was a faint but very massive galaxy. The galaxy and quasar illustrated the position of Einstein's general theory of relativity that gravity sources can bend a beam of light. The attraction of the galaxy acts as a lens, refracting the light of a distant quasar in such a way that it “bifurcates”. Even more unusual cases have been discovered. Galaxies can be positioned so that distant objects in the pictures turn into arches and even rings. In one case, a distant quasar appeared in the form of the so-called Einstein's cross, formed from four images.
Video - the structure of the Universe: