Illuminating an entire galaxy is not a straightforward task since galaxies are enormous structures composed of billions or even trillions of stars, gas, dust, and other celestial objects. Additionally, galaxies are often located at vast distances from Earth, further complicating the concept of "illuminating" them.
Light is emitted by stars within a galaxy, and it is the collective light from these stars that contributes to the overall brightness of the galaxy. The brightness or luminosity of a galaxy can vary significantly depending on its size, the number and types of stars it contains, and other factors.
To "illuminate" an entire galaxy, you would need an enormous amount of light energy. However, it's important to note that galaxies are already self-illuminating due to the stars they contain. The light from the stars within a galaxy interacts with the interstellar medium, such as gas and dust, creating various visible and non-visible emissions, including starlight, nebulae, and radiation across the electromagnetic spectrum.
Observing and studying galaxies involve capturing and analyzing the light that reaches us from those galaxies. Astronomers use specialized telescopes and instruments to collect as much light as possible over long exposure times to study the properties, structure, and composition of galaxies.
In summary, galaxies emit their own light due to the stars they harbor. To "illuminate" an entire galaxy would require an immense amount of additional light, which is not a practical or feasible endeavor given the vast scales involved.