Illustrated Astronomy/How did we get to this date?
HOW DID WE GET TO THIS DATE?
A very brief history of the Universe
Our Universe was born about 13.7 billion years ago. During the first stages, there was no matter, neither atoms, and in a certain way, all the energy, gravitational and electrical forces were all together. Then, in a matter of seconds, the very first particles formed.
It is almost unlikely to believe that, at that very moment, all the matter of the Universe was made up of hydrogen (75 %), helium (25 %), and a pinch of lithium (less than 0.001 %)[1], and a temperature of hundreds of billions of Celsius degrees.
From that moment, and for the next 380,000 years, the Universe only kept growing and getting colder, without forming any new elements.
DID YOU KNOW THAT…
the antimatter is very alike to the ordinary matter? They have the same mass in general, but they differ in their electric charge signs. For instance, both an electron and a positron (or antielectron) have opposite electrical charges. When the matter and the antimatter bind together, they annihilate each other, generating a vast amount of energy.
· At first, the formed matter and light seemed trapped. The latter collided with the first one, being incapable of travel freely as it does now. The early cosmos was so dense and hot that electrons could not remain attached to the nuclei of the atoms. However, as the Universe continued to expand and the temperature cooled down (3,000 °C approximately), the electrons started to remain next to their nuclei, preventing the light from scattering. This stage is known as Recombination or Surface of the Last Scattering since the atoms merge and, from that very moment (380,000 years after the Big Bang), light can travel freely in the Universe.
The light we detect and see today thanks to the microwave telescopes, it has traveled 13.7 billion years, and it has “cooling down” with the Universe, reaching a temperature of only 2.7 K (-271 °C).
Electrons are not bound to the atomic nuclei, and photons collide continuously with electrons and ions.
The Universe cools down. Electrons start to bind to the nuclei, and photons lose energy
The Universe is neutral, and photons don’t have enough energy to interact with atoms. Photons can finally travel freely
When light could finally escape, there were neither planets nor galaxies, and we had to wait other 200 million years before the first stars formed. During that time, the Universe was completely dark, just like a thick, darkened nocturne fog.
It is more than likely that the first formed stars were much hotter, larger, and brighter than our Sun. They needed fuel to shine, so they used both hydrogen and helium to do it. When they merged, they were creating new elements more complex, such as carbon, nitrogen, oxygen, and iron, at the same time when the Universe was releasing energy and light. These stars had very short lives, and when they died, they massively blew up, which is known as supernovae. Thus, they expelled to the cosmos the new materials they had formed, allowing the new generations of stars had access to tiny quantities of them.
Little by little, the dark Universe started to light up. After two hundred million years, the first galaxies showed up, and from then on, a new transformation began: the large amount of light that stars produce makes electrons split up inside hydrogen atoms, so the Universe is ionized again (as in the beginning), and that’s how it is up to date.
Going forward in time, the Universe continues to expand; new galaxies and stars are formed, some of them explode as supernovae and inject some other materials into the Universe; galaxies merge with each other, grow, and trigger the formation of new stars. That’s how the Milky Way, our Galaxy, arouse, which due to its shape is classified as a spiral type.
Even though it is impossible to define an exact age for our Galaxy, we can say that it is almost as old as the Universe itself. Some of the star groups orbiting the Milky Way (known as globular clusters) are nearly 12.5 billion years old.
About 4.5 billion years ago, a great cloud of gas and dust, located at one of the spiral arms of the Milky Way, started to shrink and got divided into smaller and denser clouds. In so doing, hundreds or even thousands of stars of different sizes were formed. Among them is the Sun, that since then is orbiting around the center of the Galaxy, apart from other hotter stars and many other tinnier and colder ones.
The Sun is part of the more than 200 billion stars that make up the Milky Way. It orbits around 25,000 light-years[2]away from the galactic center, and it travels at a speed of 200km/s. Completing a single orbit (cosmic year), it takes 250 million Earth years.
When the Sun was forming from its cloud, shrinking to be the size it is today, a minor part of this cloud created a disk around the Sun. Such disk originated all the planets in the solar system, from Mercury to Neptune. Every single one of them took remains of the material existing from the Big Bang, or that was once inside a star, and after thousands of millions of years, they condensed into a planet. Also, comets, asteroids, and the rest of the objects that we can find in the Solar System were formed, such as dwarf planets, where Pluto is the most known. Out of the eight planets that the Solar System has, in the third one closest to the Sun, life developed. In the beginning, 3 billion years ago, there were only bacteria, but this was increasing in time and diversifying. And today, as human beings, we can do research and understand how did we get here and amaze at everything that exists.
- ↑ A small amount of beryllium-7 was also formed, but since it was radioactive, it turned out to get discomposed into helium and lithium.
- ↑ A light-year is the distance that light takes during a year traveling in the vacuum, which is the equivalent to 9,461,000,000,000 (or 9.5 trillion approximately). It is important to remember that a light-year is a measurement of distance and not time.