How did the first galaxies form?

How did the first galaxies form?

The universe is filled with over a hundred billion individual galaxies. Most of the stars and planets in the universe are contained in galaxies. They are available in a wide variety of shapes and sizes. Some are spiral, while others are elliptical. Like snowflakes, each galaxy is unique in its own way. Where do these giant collections of stars come from and how did they form?

The first stars

The first stars to form would be blue stars with large masses. NASA

The first stars to form in the universe were nothing like our sun. They were giant massive blue stars that radiated large amounts of energy. All matter in the early universe was primarily in the form of hydrogen and helium. It is unlikely that the first stars had planets, as heavier elements are needed to form worlds, and nothing heavier than lithium has yet existed. Not long after, however, these early stars depleted their hydrogen reserves and scattered their newly formed heavy elements into space. In each star, hydrogen actively merges to form helium. This process, called fusion, is quite simple. First, you have hydrogen nuclei made up of one proton. At sufficiently high temperatures and pressures, these protons can fuse to form deuterium. Upon fusion, a proton will quickly decay into a neutron, and now atomic nuclei are made up of one proton and one neutron. Two deuteriums can then fuse to form one helium nucleus containing two protons and two neutrons. This process is what feeds the stars and also puts the star in equilibrium. The inner force of the star’s gravity is counteracted by the energy of nuclear fusion in the star’s core. Many stars will continue down the periodic table and form different elements through the triple alpha process. Once we have helium nuclei, two can fuse to form beryllium nuclei made up of four protons and four neutrons. Now a beryllium nucleus can fuse with a helium nucleus to give us the element that forms the basis of all life on Earth: carbon. During each step of this process we have a series of by-products that come in the form of small particles, the most remarkable of which is the photon, which turns into the light of the star.

The first stars would be huge, unlike anything we know in the universe today. As a result of their very high masses, the stars would be attracted to each other by their mutual gravity. Inevitably, this gave rise to the first star clusters. Star clusters have an even stronger gravitational pull than just the individual stars, and so they will also attract each other and begin to form the first galaxies. Today we are familiar with many different types of galaxies, from spiral to elliptical. However, the first galaxies would not look like many of the galaxies we can see today, as it takes many millions to billions of years to form their complex shapes. Instead, the first galaxies would look like giant star patches, unlike some of the small irregular galaxies we can see today. In addition, most galaxies would be relatively small and usually contain several million stars or less. However, the early universe was also home to a much larger number of galaxies. Because the early universe was smaller than it is now, the galaxies were much closer together. Many small galaxies will have to collide in order for small galaxies to eventually become giants today.

Colliding galaxies

Hubble made this image of two galaxies merging. NASA

Even small galaxies have a strong gravitational pull, especially compared to stars or clusters alone. As a result, galaxies are attracted to each other by their mutual gravity. Eventually, many of them began to collide and merge, increasing in relative size. During a typical galactic collision, the stars do not actually collide with each other. Although it has happened and is happening, the space between the individual stars is just too big to collide in large quantities. Therefore, perhaps a better description of these events is not as a collision, but rather as a merger. Galaxies can pass through each other several times in a gravitational dance that takes millions of years to unfold. Eventually, they begin to merge. During the fusion process, stars will not normally collide, but stellar nurseries (called nebulae) can do so, given that they are much larger than the stars they create and contain. When this happens, more hydrogen will come together to form a new generation of stars. The rate of star formation in merging galaxies will be very high, and by the end the galaxy will add millions of new stars and may even deplete most of its star-forming material. Most of the galaxies we can see, including the Milky Way, have probably merged with many other galaxies in the past. The merging of gravity and star clusters is the way the first galaxies formed.

Aiden Rempel June 16, 2022 at Science