Understanding White Dwarfs: Stellar Remnants in the Universe

White dwarfs are stellar remnants formed when stars with masses less than 9-10 solar masses exhaust their nuclear fuel. This phase marks a significant stage in stellar evolution, with approximately 97% of the stars we observe, including our Sun, eventually becoming white dwarfs. Alongside red dwarfs, white dwarfs represent some of the most numerous stars in the cosmos.

The composition of white dwarfs consists of atoms in a plasma state. As nuclear reactions cease in their cores, these stars lack an energy source to counteract gravitational collapse. Consequently, a white dwarf compresses under its own weight, leading to a drastic reduction in the distance between atoms, which restricts the movement of electrons.

The formation of these celestial bodies is a gradual process. In mature stars, the outer layers expand significantly during their transformation into asymptotic giant branch stars, eventually shedding their exhausted cores. Once fusion reactions conclude, the core contracts and heats up, but not to the ignition temperature required for the next evolutionary phase. Before reaching this temperature, electron degeneracy halts the process, resulting in the formation of a white dwarf with an initial core temperature ranging from 100 to 200 million degrees Celsius. Over time, this star will gradually cool down, and the expelled material will create a planetary nebula surrounding the white dwarf.

My understanding of white dwarfs has evolved, as I previously assumed they were small. However, some can actually be larger than Earth and even exceed the size of the Sun.

Jesús Molina Collado 1º Bachillerato B