The first galaxies or constellations in the universe formed?

Introduction to Galaxies

A huge system comprising billions of stars. Galaxies come as structures that constitute one of the majors of the universe. The galaxy is a huge and well-structured system, getting tightly bound with strong gravitational forces.

It comprises stars, gaseous clouds, interstellar gases, dust particles, plasma, and a considerable amount of dark matter. An ideal galaxy may comprise around 10 million to 1 trillion stars. All these stars are moving around a strong gravitational hub. Earlier, you might have read in different articles how a star is born, how a black hole forms, how an active galaxy becomes a dead galaxy, etc.
In today’s discussion, we shall learn how such massive structures like galaxies are formed.

The Role of Stars in Galaxy Formation

We know that the primary constituents of a galaxy are stars. Billions of stars make a galaxy. The role of stars in the formation of a galaxy is quite significant. Therefore, the exact understanding of how the stars that initiated the galaxy formation in the early universe came into existence is quite essential.

Detailed Discussion: The Big Bang and Star Formation

Since stars are the basic entities for galaxies, let’s initiate ourselves with the star-formation history. The model of Big Bang Theory initiates the universe from a single point of very high density and heat known as singularity.

At the beginning, the universe was homogeneous and isotropic, composed of very highly energized matter with high density, temperature, and pressure. This was cold dark matter now constituting 23% of the total mass of the universe.

The inflation of the universe set almost the same temperature everywhere in space. Tiny fluctuations in the density, which was mostly uniform, created in this period the seeds for further galaxy creation, i.e., the initial star formation-those which were supposed to constitute the main component of galaxies-started.

Because of gravitational forces, dark matter played a special role in attracting matter against the expansion of space and thus helping to create galaxies.

The Formation of Fundamental Particles

After the end of cosmic inflation, quark-gluon plasma filled the Universe. Sometime in depth of that plasma took place the reaction. The temperature of creation at those times was extremely high; however, the universe was lucky enough to manage the gradual cooling during expansion.

At one point, when the temperature of the Universe reached 3000 Kelvin, a so-called cooling-induced phase transition took place-the Universe underwent symmetry breaking. This is when the fundamental particles were created. Quarks and gluons combined into baryons, such as protons and neutrons. These in turn combined to make the first elements, deuterium and helium.

After approximately 380 000 years, the protons and neutrons combined to make nuclei, and electrons combined with these nuclei to create atoms. Mainly hydrogen atoms were created at this time, along with some helium and lithium atoms.

The Birth of Stars: From Gas Clouds to Nuclear Fusion

During this era first gas clouds also known as “nebulae”, began to form . They consisted mainly of hydrogen gas, about 90% of the total composition, with a little fraction helium gas, about 9%, and traces of lithium, oxygen, and other gases that consisted of about 1%.

With a rise in temperature, a gas expands, while with a drop in temperature, it contracts. Consequently, if any part of a hot nebula emits enough heat energy devoid of interference with the external surroundings, that portion starts to lose its heat and thereby contracts.
Part of a gas cloud compared to the rest of the cloud, gravitational pull acted in moving the gas and dust particles closer to each other.

These gas clouds started to clump together, and the gas particles in them moved closer to each other with an increase in their mutual gravitational pull. The increased gravitational pull brought them all together. Due to this coming together, the mass increased and with it the gravitational force grew stronger. They now had the strength to attract more distant gas particles and dust to form a huge gas clump. The friction among the matters of this clump of gas produced a tremendous amount of heat; at such high temperature, the fusion of hydrogen started, which triggered nuclear fusion reactions.

Through these reactions, hydrogen began to synthesize helium and released a tremendous amount of heat and light. Consequently, the first brilliant objects in the universe-stars-came into existence. First starts in the universe appeared roughly 400 million years after the Big Bang.

The Life and Death of the First Star

These stars formed independently in the early universe, huge in both size and mass, because the nebulae themselves from where these stars were formed were huge in nature. The larger the nebula, the more gas and dust it could gather; hence, the star which forms will have a larger mass.

The first stars that formed were a few hundred times more massive than our Sun and formed shortly after the Big Bang. As we know, with increased mass, the internal pressure and density of the star increase. Hence, they burnt out their fuel very fast. That is why all massive stars had very small life spans, lasting only a few million years, that is approximately up to 1–3 million years.

Because the stars formed in the early universe were very massive, their lives were not long since they went out quite quickly, thereby ending in a cataclysmic explosion known as a hypernova. In this blast, the star got destroyed, leaving behind a black hole. This means that the strong shockwave associated with the hypernova caused nearby gas clouds to contract. These then started forming new stars. In this way, over time, many stars came into being in the universe.

The Role of Black Holes in Galaxy Formation

This black hole suddenly developed the drawing process of all nearby stars, interstellar gases, dust, and plasma as soon as it used up all the fuel of the big star and became one. The process initiated pulling them down with its string gravitational pull. Later on, all these surrounding objects collected around the black hole.

A very strong gravitational pull made the Black Hole continuously eat up gas clouds and nearby stars till it grew into a huge object with great mass. The stars present distance away from the black hole were not able to overcome the gravitational pull exerted by it; hence, they started orbiting the black hole in an elliptical path. The objects, combined with the gravitational field of the black hole, formed a structured system called a galaxy.

Supermassive Black Holes at the Center of Galaxies

It can be said that black holes play the central role in forming such a huge, organized structure like a galaxy. Already, we know that at the center of any galaxy, usually there exists a supermassive black hole, around which all the stars in that particular galaxy orbit. The strong gravitational pull of the super-massive black hole in the middle keeps all the stars within the galaxy on track for their orbits.

While super-massive black holes reside in the centers of galaxies, they really are quite massive, and their formation was not all at once. Several intermediate-sized black holes situated in the middle of a recently formed galaxy coalesce to form one super-massive one, scientists theorize. Through millions of years, the growth of a black hole at the center of a galaxy can swallow many stars and gas clouds that, over time, grow this large.

The Oldest Galaxy: GN-Z11

Old stars torn apart in their death throes by the super-massive gravitational field of the black hole at a galaxy center-the shockwaves emanate in an energetic burst. Such shocks compress nearby clouds of gas, which in turn trigger new star birth. Thus, within a galaxy, star birth and death continue. Impossible to be certain, but the oldest galaxy discovered so far is “GN-Z11”, at about 32 billion light-years.

In fact, among those that we have seen so far, it is the oldest galaxy because the light coming from this galaxy has less redshift than other galaxies. Thus we are able to say that “GN-Z11” was probably the first galaxy which formed in the universe.