Star formation usually begins with huge molecular clouds that are mostly made up of hydrogen and some other molecules.
When an area in a molecular cloud is affected by external disturbances or internal instabilities, the density of that region begins to increase, causing the molecular cloud to collapse.
Collapse of molecular clouds
This collapse can be achieved by gravitational action and increased pressure inside the cloud.
The collapse of molecular clouds is one of the key processes in star formation.
It usually involves the action of gravity and an increase in pressure inside the cloud.
The gravitational pull of the gas and dust in the molecular cloud causes the matter inside the cloud to attract each other and gradually gather together.
Gravity is the main driving force behind the collapse of molecular clouds. The magnitude of the gravitational force depends on the mass distribution and density distribution of matter within the molecular cloud.
When a certain region of the molecular cloud begins to collapse, the density of the gas within that region increases, resulting in an increase in internal pressure.
The increase in pressure can resist the effects of gravity, but as the collapse continues, the rate at which the pressure increases often does not counteract the effects of gravity.
Under the dominance of gravity, the matter in the molecular cloud gradually gathers towards the center, forming an increasingly dense core.
This process is similar to free fall, where matter collapses towards the core at an increasing rate.
During the collapse of the molecular cloud, the spin and angular momentum of the original molecular cloud also affect the way it collapses.
Spin can lead to the formation of rotating molecular cloud cores, while the conservation nature of angular momentum can lead to the formation of disk-like structures such as protoplanetary disks.
The primitive molecular cloud may have some spin, which means the overall rotation of the cloud.
The presence of spin causes the matter inside the molecular cloud to collapse in a rotational manner.
A rotating molecular cloud core can form a rotating protostar, or a rotating structure such as a planetary disk during formation.
During the collapse of the molecular cloud, the angular momentum is conserved.
When the radius of the molecular cloud decreases, the rotational velocity increases due to the conservation of angular momentum.
This can lead to the formation of a rotating disk-like structure called a protoplanetary disk inside the molecular cloud. Protoplanetary disks are an important environment for the formation of planets and moons.
The magnetic field present in the molecular cloud can also affect the way it collapses and the angular momentum distribution.
The magnetic field can inhibit or promote the collapse of the molecular cloud through the binding of magnetic field lines and the action of magnetic field moments.
The presence of a magnetic field can lead to the rotation of matter inside the molecular cloud and the formation of a magnetic field drag.
During the collapse of the molecular cloud, there is a coupling relationship between the spin and angular momentum.
The spin can transfer angular momentum to the matter inside the molecular cloud through the action of magnetic fields and centrifugal forces.
This spin angular momentum coupling process can affect the rate and direction of molecular cloud collapse.
During the collapse of the molecular cloud, some astrophysical processes also occur, such as the cooling and recombination of matter, forming molecules, dust, and complex chemicals.
These processes can affect the rate of collapse and the physical conditions inside the molecular cloud.
The collapse of molecular clouds is a complex process that involves a variety of physical processes and interactions.
The exact details and time scales may vary depending on factors such as the mass, temperature, density, and magnetic field of the molecular cloud. Current theories and simulations of star formation are struggling to understand and explain the details and diversity of molecular cloud collapse.
Formation of protostars
Protostar formation: When the molecular cloud collapses to a high enough density, the gas and dust inside further condense to form a protostar, also known as a protostar or protostellar core.
In the core region of the molecular cloud, gas and dust condense into a denser core, which gradually increases in density and temperature, forming a protostellar core.
As the molecular cloud collapses, matter begins to gather from the outer region of the molecular cloud toward the center, forming an increasingly dense core. This core is often referred to as the protostellar core.
As matter accumulates and compresses, the temperature of the protostellar core gradually rises.
When the temperature reaches high enough, the pressure and temperature conditions inside the core can support the start of the fusion reaction. Nuclear fusion is the main source of energy inside the star, releasing energy by fusing hydrogen into helium.
Once the protostellar core begins nuclear fusion, it enters the main-sequence phase and becomes a true star.
During the main sequence phase, the core of the star continues to undergo hydrogen fusion, releasing enormous amounts of energy and light radiation.
The duration of this phase depends on the mass of the star, with the more massive stars having a shorter lifespan in the main sequence phase, while the less massive stars have a longer lifespan.
Protostars will gradually deplete the hydrogen fuel of their core as they burn hydrogen during the main-sequence phase.
When the hydrogen in the core is depleted, the star undergoes further evolution, which may expand into a red giant, undergo nuclear fusion reactions, and eventually evolve into a white dwarf, neutron star, or black hole.
These processes are general models of star formation, but the specific details and time scales may vary depending on factors such as the nature of the molecular cloud, environmental conditions, and stellar mass.
Star formation is a very complex and wonderful process in the universe, which is of great significance for understanding the evolution of the universe and the formation of galaxies.
Formation of stars
The formation of stars began in the early days of the universe, between a few million and billions of years after the birth of the universe.
Based on current cosmological models and observational data, we believe that the main periods of star formation occurred in the early stages of the universe, from about 13.8 billion years ago to about 3.7 billion years ago.
At about 380,000 years of the age of the universe, the temperature and density of the universe have been reduced to low enough levels for hydrogen and helium atoms to form. This period is known as the period of cosmic reunion.
As the universe expands and cools further, primitive density perturbations begin to form in the universe and gradually evolve into denser regions that eventually become the seeds of star formation.
The exact timing and process of star formation can vary in different galaxies and environments.
In the early universe, star formation tended to occur during the formation of large-scale structures, such as galaxy clusters, groups of galaxies, and primordial galaxies.
The gases and matter in these massive structures gradually aggregate through gravity to form stars.
It is important to point out that star formation is an ongoing process that has been going on since the early days of the universe to the present.
In the current galaxy, there is still activity in star formation, especially in interstellar clouds and interstellar media in galaxies.
These newly formed stars will continue to influence the evolution of galaxies and the evolution of the universe.
Star formation began in the early days of the universe and continued throughout the evolution of the universe.
Early star formation occurred mainly within billions of years after the cosmic recombination period, while there is still star-forming activity in the current galaxies.