The proposals put forward by the majority of astronomers are that the formation of Galaxies occurred following a cosmic “big bang”, which took place some 10 to 20 billion years ago, and led to the beginning of the universe. Immediately after this explosion, within milliseconds, gases in the form of a mass of fog started to join together, disintegrate and condense, under gravitational force, leading to the formation of the building blocks of the galaxies.
Scientists are of different opinions, regarding the formation of the galaxies. According to certain scientists, initially, tiny clusters of around 1 million stars, called globular clusters were formed and in due course, they combined together as galaxies. The opinions of the rest were that the formation of galaxies took place at the beginning.
Following the Big Bang, subatomic particles and radiations together created the Universe. The succeeding events were under debate – was it the tiny particles that gradually joined together and slowly formed stars, then a cluster of stars leads to the formation of galaxies? Or was it the universe that combined together, forming massive tufts of matter that in the long run, split up into galaxies.
The Anatomy of a Galaxy
A configuration of stars, stellar remnants, dust, interstellar gas and dark matter, bound together forms a galaxy. The Galaxy is the derivation of the Greek galaxies, apparently “milky”, this is referred to the Milky Way.
Sizes of Galaxies
The variation in the sizes of the Galaxies differs from some thousands (103) stars to giant size measuring one hundred trillion (1014) stars, each cluster of star orbits around their galaxy’s mass center. It is believed that several galaxies possess black holes, where the center is active. The mass of the central black hole of the Milky Way, called Sagittarius A*, is 4 million times bigger than the Sun.
For instance, the age old and the farthermost galaxy EGSY8p7 which has a light traveling distance of 13.2 billion light-years from the Earth, was noticed on July 2015, and it has existed for 570 million years, following the Big Bang. Earlier, in May 2015, the furthermost galaxy EGS-zs8-1 ever known, approximated, possessing a light traveling distance of 13.1 billion light-years away and that it possessed 15% of the Milky way’s mass.
We exist in more or less the inaccessible arm of the Milky Way.
The main classification of the Galaxies is: elliptical galaxies, spiral galaxies and irregular galaxies.
The Spiral Galaxies, have a flat disk, whose center is protruding and with spiral arms all around. The galaxy disc comprises of planets, stars, gas and dust – all these circles in an orderly manner about the center of the galaxy.
The rotating speed of hundreds of km, per second is likely to lead the matter contained in the disk to have a characteristic spiral form, similar to a cosmic pin wheel. The form of certain spiral galaxies is still more fascinating, because of which they achieve explanatory names, like sombrero galaxies.
The age old stars remain within the protruding center of the galactic disk. Several newly formed stars acquire the spiral form, moreover their disks are encircled with a halo, and scientists consider them wealthy possessing strange dark matter.
Differently speaking, the Milky Way, which is our galaxy, is peculiar: it possesses 100’s of billions of stars, dust and sufficient gas for the formation of billions of stars more, to a minimum of 10 times the dark matter, more than the sum of the gas and stars combined. All of these stay in position, by the gravitational forces acting on them.
The Milky Way acquires a spiral form with 2/3rd of its galaxies that are known. A great amount of energy, and at times, glowing flames are created at the center. Referring to the enormous gravity, it is supposed to possess, the explanation of the energy that is given out and the movement of the stars, all put together made the astronomers arrive at the conclusion that the central portion of the Milky Way is a marvelous gigantic black hole.
There are chances for the Milky Way owned by us to merge, some day, with the Andromeda galaxy- that is only 2 million light-years distant from us and that is visible to our naked eye from The Northern Hemisphere of the Earth.
These processes between galaxies, are supposed to evolve from a division of the evolutions of nature, wherein galaxies that are not in the regular form, gets transformed into different forms, whereby spiral galaxies ultimately according to the conviction of scientists, change into elliptical galaxies
Elliptical galaxies are elliptical in shape as implied by their name. Normally, they are round in shape, however, they elongate along an axis longer than the rest. At times they appear approximating a round shape, and at times stretched in the form of a cigar
In the Elliptical galaxies, we find several age old stars, nearly one trillion in numbers, however, along with much interstellar matter and dust particles. Their stars circulate about the center of the galaxy, similar to that of the disk of the spiral galaxies, however, in better random directions. Some of the recent stars are believed to acquire elliptical shape galaxies.
The giant elliptical galaxies are the universe’s biggest ones acknowledged. They are expected to have a length of 2 million light-years. There are possibilities for the elliptical galaxies which are tiny, to double the dwarfed elliptical galaxies.
This variety is exhibited in the Hubble Ultra Deep Field (HUDF). Hubble in his investigation, observed a small patch of sky (1/10th the moon’s diameter) within 1 million second (11.6 days) and identified about 10,000 galaxies, comprising of different shapes, sizes and colors. Viewing from the ground, we observe just a little in this patch; they are in the constellation Fornax (Fornax, in the southern sky, is a constellation)
Irregular galaxies are those that are neither elliptical nor spiral in shape. They become visibly irregular in shape, without a definite shape, since they are mostly surrounded by the gravitational forces of the nearby galaxies.
Certain galaxies arise in isolation in pairs; however, they are mostly divisions of bigger union, called clusters, groups and super clusters.
Galaxies in these clusters mostly mingle together and perhaps merge between them in an active cosmic dance of interrelated gravity. This merging leads to the flow of gases along the galactic center; it may activate phenomena such as rapid star formation
The forms of the galaxies are prejudiced by their nearby ones, galaxies frequently collide. The Milky Way, by its own collides with their neighbor, the Andromeda galaxy. Hubble identification brings out the fact that despite Andromeda galaxy and the Milky Way being of equal age, the stars in Andromeda’s halo are comparatively of less age than those of the Milky Way. Based on this identification along with other proofs, astronomers deduce that Andromeda had earlier jammed into a minimum of one or more galaxies.
100 years earlier, Einstein established his theory of General Relativity, substituting the Newton’s notion of time and absolute space with lively material – space, time – that besides relying on the matter-and-energy it contained, may contract or expand according to the universal characteristics. Theorists, such as Willem de Sitter, Alexander Friedman and Georges Lemaitre dealt with several mathematical problems and their results, however, Edwin Hubble was the only one along with his 100-inch telescope on the top of Mt Wilson, who revealed to us the Universe the way we come to know of it at present.
Having a glance of the galaxies at a distance – the spirals (and elliptical latter) in the middle of the night sky – Hubble for the first time, succeeded in inferring that the Universe was expanding, and also succeeded in calculating its rate of expansion. His conclusion was the farther the galaxy appeared to us, it appeared to move at a greater speed from us.