They study distant galaxies because they want to know whats out in other galaxies and how many planets it has
That is impossible to answer because scientist don't know ALL the galaxies.
Changes in the light from distant stars and galaxies can be caused by several factors, including intrinsic variations in the stars themselves, such as pulsations or eruptions, which can alter their brightness. Additionally, gravitational lensing can bend and magnify light from distant objects due to the presence of massive foreground objects. Cosmic events like supernovae also lead to dramatic changes in brightness. Lastly, the redshift effect, caused by the expansion of the universe, can alter the observed wavelength of light from distant galaxies.
The light from distant galaxies is redshifted. The only reasonable explanation for that is that the galaxies are moving away from us.
Moving away from us
The visible part of distant galaxies is the collection of stars, gas, and dust within the galaxy. These components emit light that reaches our telescopes, allowing us to observe and study the structure and properties of the galaxies.
The light from distant galaxies shows redshift because the universe is expanding. As the galaxies move away from us, the light they emit gets stretched, causing its wavelength to increase and shift towards the red end of the spectrum. This redshift can help scientists determine the velocity at which galaxies are moving away from us and provide insights into the expansion of the universe.
The apparent redshift is caused by the Doppler Effect; the frequency of waves is increased by an approaching source and decreased by a leaving source. Since the fgrequencies we see from stars are slightly lower than they should be, we know that the stars and other objects are moving away. The Doppler Effect causes changes of light emanating from distant stars and galaxies.
The "redshift" refers to the fact that the light is less energetic than when it was emitted; it shows that the galaxies move away from us. Should a galaxy move towards us - which is possible only for galaxies that are relatively close to us - then there would be a blueshift.
The expansion of space causes a redshift in the light from distant galaxies due to the stretching of wavelengths as the universe expands. As light travels through expanding space, its wavelength increases, shifting it toward the red end of the spectrum. This phenomenon, known as cosmological redshift, occurs because the space between galaxies is increasing, leading to longer wavelengths by the time the light reaches us. Consequently, more distant galaxies appear redder, providing evidence for the expansion of the universe.
The bending of light due to great masses is called Gravitational MicroLensing.
visible light
When light from distant galaxies is shifted towards longer wavelengths, this phenomenon is known as redshift. It occurs due to the expansion of the universe, causing galaxies to move away from us. As a result, the wavelengths of the emitted light stretch, indicating that these galaxies are receding. Redshift is a key piece of evidence supporting the Big Bang theory and helps astronomers determine the rate of expansion of the universe.