Its an empty vacuum, There is nothing there. Literally nothing.
Yes, stars can exist outside of a galaxy. These stars are typically referred to as intergalactic stars, and they may have been ejected from their original galaxy due to interactions with other stars or galactic dynamics. Intergalactic stars are typically found in the space between galaxies.
solar system
in the halo
It has been estimated that there are between 200 -> 400 billion stars in the Milky Way Galaxy
between 200 and 400 billion stars
The dust and gas located between stars in a galaxy is called the interstellar medium (ISM). This material plays a crucial role in the formation of new stars and planets within the galaxy.
That means matter between stars - mainly dust and gas.
A typical galaxy may have anywhere between a few million (106) stars, and over a trillion (1012) stars. Our own Milky Way is estimated to have between 200 and 400 billion (2x1011-4x1011) stars.
Most new, young, stars can be found in the arms of spiral galaxies
Large stars are distributed all over our galaxy, there is no single location for them.
A galaxy is by a definition a group of stars. If there were no stars it could not be a galaxy.
A dwarf galaxy might contain this number of stars. A galaxy will contain billions of stars.