There are about 4.1e14 seconds in 130 million years. The two seconds delay is thus very small. I wonder what is the role of the fact that interstellar vacum is

There are about 4.1e14 seconds in 130 million years. The two seconds delay is thus very small. I wonder what is the role of the fact that interstellar vacum is not an absolute vacum. I read some where that there is about one atom in each square cubic cm. The number of cm in one light year is 9.4605284e17.