Population I refers to the newest and most common type of star in the universe. The first ones being less than ten billion years old, with the newest stars being created up to this day. They are metal-rich, meaning they contain a higher proportion of elements heavier than helium compared to the previous two populations. They are primarily found in the disk of galaxies, especially concentrated in the spiral arms, where star formation is still happening. One of the most well-known examples of a population I star is our sun. Despite it being our basic reference for how stars operate, our sun has significantly higher metrics in both temperature and size compared to the typical Population I star; the vast majority of which (possibly more the eighty percent) being small, cold and less luminous bodies known as "Red Dwarves."
The exact dating on the formation of population II stars is something of a mystery, what is known is that they most likely came hundreds of millions of years after the first (more hypothetical) population III stars. Though having some amount metal, they are still from an era in which all, but the most basic elements were a rarity, formed from the materials released by the supernova of population III stars. Though there is variation in color they tend redder color their younger population I counterparts due to lower temperatures and are typically found clustered together in areas of more ancient star formation, such as the galactic bulge at the center of the milky way galaxy. While no remaining population III star has ever been discovered or documented the study of these can give us great insight into the nature of the early universe.
After the rapid creation following the big bang, the universe went into a period known as the "Cosmic Dark Age." Lasting hundreds of millions of years the cosmic cooling that first allowed for the rapid bonding of new particles had frozen the pace of advancement to a cosmic crawl, with nuclear forces having played their part, gravity began to slowly bring together the pieces that were left. Primarily composed of an undetectable substance known as "dark matter" galaxies are collections of stars and the things that orbit them, pulled together into a cosmic superstructure around a center of mass, usually some form of supermassive black hole. The region around this center of mass is known as a galactic nucleus, either being active or not active. Active galactic nuclei are constantly emitting electromagnetic radiation, manifesting in every way from quasars, the single brightest objects in the known universe, to the "little red dots" that have puzzled astronomers observing the early universe. The most widely used system of classification for galaxies is the "Hubble Sequence;" placing galaxies into three main categories based on look. One: Elliptical, having a simple circular to elliptical structure, two, Lenticular with a "disk" structure and three: Spiral, with the well-known spiraling pattern exhibited by the milky way.
Stars are in essence giant nuclear fusion reactors. Most initially use hydrogen as fuel, fusing them to create helium; when the hydrogen begins to run out and if the core has a hot enough temperature, they can fuse the helium into heavier elements, such as carbon or oxygen. Once the star begins to run out of Helium this process, if the star contains to requisite mass and temperature to facilitate it, continues creating heavier and more complex elements after burning through the last ones, topping out around the isotope Iron-56. To move beyond that 56-baryon barrier requires exponentially greater power, the only way to achieve that is a supernova. The release of energy after the death of a star is what allows for the forging of the rest of the naturally forming elements in what is known as "Supernova nucleosynthesis."
The conditions of the early universe were initially rather hostile to the formation of the stagnant entities such as planets, the extreme heat and simplistic elements available led to the creation of the paradoxically much more complex systems of the star first. Only within the cloud of cosmic dust leftover by the supernova of a dead star did the quantities of heavy elements cross the threshold for the creation of the first planets. In these cosmic clouds the few elements able to condense tend to be slowly brought together to form what is known as a "Protoplanetary Disk." This disk will typically rotate a newly formed "Protostar" also formed from pieces of the nebula. These entities will over the course of millions of years condense into their more recognizable planetary and solar forms with the majority of the nebula being expelled out into the universe, possibly to be incorporated into stars elsewhere.
Supernovae are logically as old as the stars that precede them, but the oldest one we have directly observed was just recently discovered by NASA with the James Webb Space Telescope, it being 13 billion years old, dating only around 700 million years after the creation of the universe. When certain stars die, they can release large amounts of energy in a mass explosion. These explosions are split into two categories and numerous subcategories, Type 1 leaving no evidence of hydrogen after the event and type two: leaving some behind. Type 1-A occurs when a small ultra hot star known as a "white dwarf." end up accumulating too much material and experiencing runaway fusion. Type 1-B and C occur when the sheer gravitational force of an ultra-massive star crushes its own core after the stripping of the star's outer layers (Hydrogen in 1-B, Hydrogen and Helium in 1-C.) Type 2 supernova only occur in truly massive stars. After they burn through their first fuel sources (Hydrogen, Helium) they slowly shift to ones that expel less energy (Oxygen, Neon) and finally ones that consume energy (Iron.) This leads to less support for the outside of the star from the core, causing a collapse.
The big bang led to the creation of few, very simple elements. In the earliest "days" the universe was almost entirely Helium and Hydrogen with some trace insignificant amount of lithium and beryllium. These basic gases slowly congregated together as the universe cooled forming a kind of star known as "population III." With no solid or metal contaminates they could grow to supermassive sizes, up to hundreds of times that of the sun. These massive sizes led to greatly decreased lifespan; they would typically only last a couple million years before collapsing. Inside their cores heavier elements, far more complex than the basic few birthed in the seconds after the creation of the universe would begin to form through a process known as "stellar nucleosynthesis."
Black holes are regions of space where gravity becomes so intense that nothing, including light itself can escape, leading to the "black void" look. They are created under exceptional circumstances, when matter is compacted into a dense enough point it can form what is known as a "singularity" a point of near infinite density, enough to create an unescapable gravitational pull within an invisible boundary known as an "event horizon. Traditionally the conditions to create black holes were thought to primally occur via the collapse of stars, though these "Steller mass" black holes still most likely make up the vast majority of black holes in our galaxy, most experiencing a force known as "natal kick" after their creation and being scattered to the edges of the milky way, possibly hundreds of millions existing. Modern scholarship points to a variety of possible origins for differing kinds. "Primordial" black holes could have been some of the first things created in the universe, being born less than a second after the big bang. In the early universe the sheer quantity of newly created matter in the relatively small space could have led to the conditions for collapsing into singularity.
Nucleosynthesis is exactly what it sounds like, the synthesis of atomic nuclei. Big bang Nucleosyntheses was the creation of the first most basic elements in the minutes after the creation of the universe. For a short period of time the universe was cool enough to allow for nuclear binding but warm enough to facilitate rapid nuclear fusion. During this brief window protons and neutrons combined to form the first stable atomic nuclei, primarily and helium and hydrogen (hydrogen nuclei just being the leftover single protons) with small amounts deuterium, and trace lithium. After further cooling this rapid synthesis would cease. While the creation of these first elements would take only minutes, the rest would have to wait a couple hundred million years until the supernova of the first stars.
As the universe cools the quarks start to form into protons and neutrons, a kind of higher order particle known as Hadrons. These were bound by the strong nuclear force, facilitated by fundamental particles known as gluons. Protons formed by two up quarks (each with a positive charge two-thirds of the elementary charge) and one down quark, (with the negative charge of one third that of the elementary charge) making the particle positively charged. Neutrons having the opposite arrangement, two down quarks and one up, making them have no charge. As the cooling continued these particles bound together making the first atomic nuclei, and over hundreds of thousands of years, spaced cooled enough for electrons to begin to orbit these nuclei, creating the first true atoms
