Do stars vary their own brightness? All I could find on the internet was about how stars vary in brightness depending on their distance to Earth, temperature, type of star...

But my question is, can a star can change its brightness.
They can, and some do. These stars are called variable stars, because their luminosities as observed from Earth vary over time, often (though not always) in a regular period. Here are some broad categories:


Pulsating stars, where fluctuations lead to increases and decreases in size or temperature, which in turn produce changes in the star's brightness. Example: The oft-cited Cepheid variables.
Eclipsing binary stars involve two stars orbiting each other. When one passes between the other and Earth, the combined luminosity of the system appears to decrease, even though the stars' intrinsic luminosities are probably constant. Example: Algol.
So-called eruptive variables (often lumped together with cataclysmic variables, which are different) may have irregular outbursts caused by flares or other phenomena. Example: Luminous blue variables (LBVs).


The change in brightness and the length of the variations depend on the type of variable star in question. The luminosity can vary by anywhere from a fraction of a magnitude to many magnitudes. Likewise, the period (if there is one) can range from hours to years.