A red dwarf star.
See related question.
Correct. M-type stars on the main sequence are called red dwarfs.
None of them are cool and dim; the one in the white/black dwarfs are cool and dim.
No. All stars are hot. For stars on the main sequence, the largest it is, the hotter it is. When a star leaves the main sequence to become a giant or supergiant it will cool down, but will remain hot enough to glow brightly.
Low-mass stars, like red dwarfs, are likely to spend the longest time on the main sequence due to their lower energy consumption and slower nuclear fusion processes. These stars have the longest lifespans because they burn their fuel at a slower rate compared to more massive stars.
The oldest stars are typically red dwarfs, which are small, cool, and faint stars that have long lifespans. White dwarfs are the remnant cores of low to medium mass stars, not the oldest. Giant stars are intermediate stage stars that have evolved away from the main sequence.
The lower right part of the main sequence in the Hertzsprung-Russell diagram contains the stars that took the longest to reach the main sequence. These stars are low mass and cool, so they undergo a longer contraction phase before they start fusing hydrogen in their cores and settle onto the main sequence.
Most stars are plotted along the main sequence in the Hertzsprung-Russell (HR) diagram, which extends diagonally from the upper left (hot and luminous stars) to the lower right (cool and less luminous stars). This is because the majority of stars, including our Sun, spend the majority of their lives in the main sequence phase where they are fusing hydrogen into helium.
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).
Cool red giant stars are located in the upper right corner of the Hertzsprung-Russell diagram, where they are both cool (low temperature) and bright (high luminosity). These stars have evolved from main sequence stars and are in a late stage of stellar evolution.
Large cool stars are classified as either K or M type stars on the spectral classification scale, with M stars being cooler and redder than K stars. These stars are part of the main sequence on the Hertzsprung-Russell diagram and have surface temperatures lower than 5,000 K.
Our sun is a typical star compared to others in the universe. It is a G-type main-sequence star, similar in size, age, and composition to many other stars. It is not particularly large or small, hot or cool, bright or dim in comparison to the billions of stars in the galaxy.
Stars that are cool and dim would be found in the lower right corner of the Hertzsprung-Russell diagram, in the region known as the "lower right" or "lower main sequence." These stars have low luminosity and temperature compared to other stars on the diagram.