Simply, because they are the hottest and thus the most luminous.
The Sun, classified as a G-type main-sequence star (G dwarf), has a surface temperature of about 5,500 degrees Celsius and a luminosity of 1 solar unit. Compared to other main-sequence stars, the Sun is relatively average; hotter stars, like O and B types, exhibit much higher temperatures and luminosities, while cooler stars, such as K and M types, have lower temperatures and luminosities. Overall, the main sequence shows a correlation where higher temperatures correspond to greater luminosity, with the Sun positioned in the middle of this range.
Main Sequence
Main Sequence stars can be any spectral class of star. Something that might help you in the future is when you look up a star and see its spectral class, its always followed by a roman numeral to define where the star is in its life and size and they go as follows. I-a= A hyper Giant Star I-b= A very bright Super Giant star I= A normal Super Giant star II= Bright Giant star III= Giant star IV= Sub Giant star V= Dwarf Star(which this is where most main sequence stars fall into, While a main sequence star could also be one of the classifications listed above. it just depends on its spectral class. for example the star Deneb is in its main sequence still and its classified as a hyper giant) VI= Sub Dwarfs (this is a very rare classification and are mostly used for brown dwarfs. I hope this helps mate.
The Sun is a as a G2V type star, a yellow dwarf and a main sequence star. Stars are classified by their spectra(the elements that they absorb) and their temperature. There are seven main types of stars. In order of decreasing temperature, O, B, A, F, G, K, and M
Small hot stars are classified as type O, B, or A stars based on their spectral characteristics. These stars are typically blue-white in color and have high surface temperatures and luminosities. They are also referred to as main sequence stars because they are actively fusing hydrogen into helium in their cores.
T Tauri stars are pre-Main Sequence stars which are large but not as hot as O and B Main Sequence stars. They mainly fall in the categories of F, G, K or M, and they are not yet on the Main Sequence because they are still accreting mass and are still very young and unstable.
See related question
All stars that are in hydrostatic equilibrium are on the main sequence, where outward thermal pressure from the hot core is balanced by the inward gravitational pressure from the overlying layers.See related questions
The seven types of main sequence stars in the universe are O (blue and hot), B (white-blue and hot), A (white and hot), F (yellow-white and medium), G (yellow and medium), K (orange and cool), and M (red and cool).
The Sun, classified as a G-type main-sequence star (G dwarf), has a surface temperature of about 5,500 degrees Celsius and a luminosity of 1 solar unit. Compared to other main-sequence stars, the Sun is relatively average; hotter stars, like O and B types, exhibit much higher temperatures and luminosities, while cooler stars, such as K and M types, have lower temperatures and luminosities. Overall, the main sequence shows a correlation where higher temperatures correspond to greater luminosity, with the Sun positioned in the middle of this range.
Main Sequence
Main Sequence stars can be any spectral class of star. Something that might help you in the future is when you look up a star and see its spectral class, its always followed by a roman numeral to define where the star is in its life and size and they go as follows. I-a= A hyper Giant Star I-b= A very bright Super Giant star I= A normal Super Giant star II= Bright Giant star III= Giant star IV= Sub Giant star V= Dwarf Star(which this is where most main sequence stars fall into, While a main sequence star could also be one of the classifications listed above. it just depends on its spectral class. for example the star Deneb is in its main sequence still and its classified as a hyper giant) VI= Sub Dwarfs (this is a very rare classification and are mostly used for brown dwarfs. I hope this helps mate.
The Sun is a as a G2V type star, a yellow dwarf and a main sequence star. Stars are classified by their spectra(the elements that they absorb) and their temperature. There are seven main types of stars. In order of decreasing temperature, O, B, A, F, G, K, and M
Procyon is actually a binary Star System in the Canis Minor constellation. Both Procyon A and Procyon B are white stars. A is a Main sequence (still converting Hydrogen to Helium) Star and B is a white dwarf.
The star 61 Cygni B is estimated to have a main sequence lifetime of approximately 10 billion years.
Nu Capricorni (Alshat) is a binary star in the constellation Capricornus.It is a binary star system.ν Capricorni A is a blue white type B, main sequence dwarf.ν Capricorni B (little is known about the composition)
Small hot stars are classified as type O, B, or A stars based on their spectral characteristics. These stars are typically blue-white in color and have high surface temperatures and luminosities. They are also referred to as main sequence stars because they are actively fusing hydrogen into helium in their cores.