A supercluster is a group of galaxies that are very large and organized. They are usually found near the centers of large galaxies.
A trillionth of something is a very small amount. To say that something is a trillionth of something is to say that it is very, very small.
The subatomic level is the smallest level of the universe that we can see or measure. At the subatomic level, particles like atoms are still moving around.
A thing is gravitational if it attracts other things towards it. The Earth is gravitational, because it attracts objects towards it.
Irretrievably means that there is no way to fix or recover from the situation. The ship was irretrievably lost in the storm.
When you say that someone's footsteps are on your doorstep, you are saying that they are close to you. This can be a warning or a declaration.
Unoriginal means that something is not very creative or innovative. Sometimes people use the word to describe something that is not very good or enjoyable.
An astrophysicist is a scientist who studies the stars. They might study the stars in order to learn more about the universe, or they might study the stars to learn more about the Earth.