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The Milky Way has about 100 billion 400 billion stars (at least the same number of planets), and there are about 200 billion 2 trillion galaxies in the observable universe. 
Stars are the most complex objects in the universe, with their life cycles ranging from being born in molecular clouds, passing through the main sequence stage, and finally evolving into giants, planetary nebulae, white dwarfs, neutron stars, or black holes.
Specifically, there are the following distinctions:
Stars are divided into stages: (novae, main-sequence stars), giants, supernovae, (white dwarfs, neutron stars, black holes).
Planets are divided into Jupiter-like planets and terrestrial planets according to their composition
Nebula
Nebulae are huge cloud-like structures of gas and dust in the universe, which are collections of interstellar matter, formed by gravitational pull, pressure fluctuations, or the interaction of interstellar matter, and within the nebula can give birth to new stars or planets.
Stars
Nova
Nova is a star system that usually consists of two stars that are attracted to each other and orbit each other, one is the main sequence star and the other is a white dwarf, when the white dwarf absorbs a large amount of gas from the surface of the main sequence star, it can trigger a nuclear fusion reaction, causing the nova to explode.
Usually lasting anywhere from a few days to a few months, the eruption does not lead to its complete destruction, it is a repeatable astronomical phenomenon that may erupt again, just less frequently.
Main sequence star
Main-sequence stars are a stable stage in the evolution of stars, accounting for most of the star's overall lifespan, which can be billions to tens of billions of years. Stars at this stage convert hydrogen into helium through nuclear fusion reactions to produce energy and light radiation, and when the hydrogen fuel in the core is depleted, it begins to enter subsequent evolutionary stages, such as the giant phase or the white dwarf phase.
According to the temperature and spectral color of the surface of the main-sequence stars, the order from hot to cold is O, B, A, F, G, K, and M.
Type O main-sequence stars are the hottest, with very high surface temperatures and a blue color, but they have the shortest lifespan.
G-type main-sequence stars are moderately warm, yellow, and have a long lifespan, generally billions of years.
M-type main-sequence stars are the coldest, red, and are the most numerous main-sequence stars in the universe, and about 70-80% of the stars in the Milky Way are M-type, and it has a very long lifespan, which can reach tens of billions of years.
The Sun is a medium-mass g-type main-sequence star that is currently in a stable hydrogen combustion phase.
Superstar
A giant star is a stage after the evolution of a main-sequence star, usually a star that has depleted its core and begun to burn outer helium or heavier elements. This phase is characterized by the expansion of stars, a decrease in surface temperature, but an increase in total luminosity.
Low- to medium-mass stars, such as the Sun, evolve into red giants that emit red or orange light. Massive stars evolve into blue giants, which have higher surface temperatures and brightness, emitting bluish or white light.
At the end of giant star evolution, some of the less massive giants may become white dwarfs, while the more massive giants may explode into supernovae, leaving behind neutron stars or black holes.
White dwarfs
White dwarfs are the remnants of small and medium-mass main-sequence stars (usually less than 8-10 times the mass of the Sun) in the late stage of star evolution, and the radius of the stars at this stage is small, but the density is very high, reaching thousands to tens of thousands of kilograms per cubic centimeter.
In the later stages of evolution, white dwarfs will gradually cool down and eventually become black dwarfs, which are completely cooled white dwarfs that no longer emit light, but this evolution process may take tens of billions of years.
Supernova
A supernova is the ultimate stage in the evolution of stars, marking the end of their lives for certain stars in spectacular ways**. This release of energy can reach billions of times the total energy of the entire life cycle of the sun, and may even be brighter than the entire galaxy for a period of time.
Supernovae** disperse large amounts of heavy elements into the interstellar medium, providing the necessary raw materials for the formation of new stars and planets, leaving behind debris that can form neutron stars or black holes.
Neutron stars
Neutron stars are extremely compact objects formed by the gravitational collapse of the core debris of the massive star in the process of star evolution after running out of fuel and a supernova** occurs.
Its density can reach hundreds of millions of tons per cubic centimeter, the matter inside is compressed into neutron degenerate states, its surface temperature is hundreds of thousands of degrees, and its magnetic field is hundreds of millions to billions of times stronger than the Earth's magnetic field.
Black holes
Black holes are usually made up of extremely massive stars, and after a supernova**, the core debris is unable to resist gravity and collapses, resulting in the formation of black holes. A black hole is an extremely dense celestial body with a very strong gravitational pull, and the surface of the black hole is called the event horizon, a kind of region from which even light cannot escape.
Black holes are divided into three main types based on their mass and how they form: stellar-mass black holes (formed when stars collapse), intermediate-mass black holes (the mechanism of formation is not yet known), and supermassive black holes (present at the center of galaxies with masses ranging from millions to billions of solar masses).
Black holes cannot be directly observed, but they can be indirectly observed and proven by detecting the motion of matter near the black hole, gravitational waves, X-rays or gamma rays and other high-energy radiation sources.
Planets
Terrestrial planets
Earth-like planets are those that are similar to Earth and may have Earth-like conditions made of rock and metal, geological formations, and atmospheric conditions.
A popular target for the search for extraterrestrial life, and while there are no direct observations of extraterrestrial life, scientists believe that terrestrial planets offer the most promising opportunities to find life.
Jupiteroids
Juvian planets are large and extremely massive planets with a predominantly gaseous and liquid substance. These planets are mainly composed of hydrogen, helium gas, and some icy materials such as water, ammonia, and methane, and have no solid surface, but are one or more layers of atmosphere that gradually transition down to a possible rocky core.
The study of Jupiters is of great significance for understanding the formation process of planets, atmospheric dynamics, and the chemical composition of the universe.